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The plurality of forms: now and then.

HOW MANY ESSENCES does a natural kind have, one or many? In this paper I address an argument of Hilary Putnam to the effect that the plurality of modern sciences shows us that any natural kind has a plurality of essences. Putnam argues for this claim in the context of objecting to what he takes to be the Thomistic assumption of a single essential or substantial form for any particular natural kind. (1) Putnam's objection to the Thomist is prompted by his longstanding worries about how language or the mind "hooks onto the world." (2) He has argued that no system of representations, mental or linguistic, could have an intrinsic relationship to the world. He has long used "Aristotelian" as a descriptive term applied to representationalist accounts of mind and language that appear to suggest such a built-in relationship.

However, Putnam now grants that the Thomistic notion of form and its application to the identity of concepts may avoid the earlier objections he directed at what he called Aristotelianism. In this concession, he has in mind the Thomist thesis that the mind's concepts are formally identical to and determined by the objects in the world that fall under those concepts, what I will call the concept identity thesis (CIT). When we use a term like "dog," it succeeds in referring to dogs because the concept we have in mind is in some fashion formally identical to dogs. This looks like a powerful candidate for an intrinsic or built-in relation to the world on the part of concepts. Having granted CIT to the Thomist, Putnam now looks to defeat the Thomist's position on other grounds. Now he objects that the various different sciences of today reveal a multitude of essences for any particular natural kind. The application to the Thomist is straightforward. The advance of the sciences has shown us that there are too many substantial forms in any particular kind of thing to provide the unity of conceptual identity required by the Thomist's account. To put it plainly, Putnam denies or at least doubts that "substances have a unique essence" (3) that could provide formal identity conditions for the concepts under which those substances fall. In this regard, the dispute between Putnam and the Thomist is of great contemporary relevance, insofar as it bears upon longstanding questions in the philosophy of science, the philosophy of biology, and metaphysics.

To address Putnam's objection, I will begin by describing his argument. A striking feature of his argument is the family resemblance it bears to a set of arguments Aquinas faced in the thirteenth century that also argued for a plurality of essences or substantial forms for the natural kind human being. This parallel suggests that a look at Aquinas's own arguments against the pluriformists or pluralists may prove helpful for providing philosophical resources for responding to Putnam in the twenty-first century. Thus, I will examine the famous plurality of forms position that Aquinas argued against in the Summa Theologiae in order to acquire reources useful for responding to Putnam. Finally, I will consider a particular case of recent scientific practice, in order to apply the results of my examination of Aquinas's arguments to the broader contemporary situation brought to our attention by Putnam's obejction, and to suggest whose position, Putnam's or the Thomist's, more adequately captures the practice of the natural sciences as we see them practiced today, and their bearing upon the metaphysical question of the nature of essence in natural kinds.


Putnam's Argument for the Multiplicity of Substantial Forms. Putnam states his objection to the Thomist as follows: "The greatest difficulty facing someone who wishes to hold an Aristotelian view is that the central intuition behind that view, that is, the intuition that a natural kind has a single determinate form (or 'nature' or 'essence') has become problematical." (4) He believes there is a philosophical consensus in modern thought that, given the plurality of modern sciences under which some object in a natural kind may fall, we must recognize a plurality of essences for that object, one each for each science. Putnam uses the example of his dog Shlomit. (5) Take just two of the natural sciences that may investigate the nature or essence of dogs, evolutionary theory and genetic theory. According to Putnam, each of these discourses will claim to be telling us what is essential to being a dog. The evolutionary biologist will say that it consists in a certain history of descent shared by the members of a certain population that is the natural kind, and will discount genetic structure. The geneticist will say that it consists of a certain genetic structure shared by the members of the set of dogs constitutive of the natural kind, and will discount evolutionary descent. If we look directly at the essential descriptions, prima facie their conceptual contents are not identical one to another. To the extent that any particular science, genetics, for instance, does not contain within itself the principles of the other science, evolutionary theory, for instance, it cannot include information based upon those other principles within its essential description.

Here we have to be careful of an ambiguity in the example, since not including a feature in one's consideration of an object should not be confused with excluding it from the object that is considered. In examining an apple within some discourse, biochemistry, for example, perhaps I will not include within my biochemical consideration of it that it is red. Perhaps I will consider that feature in botany. But by not including it in the one consideration, I have not excluded it from the object that I consider. Not including it, I have made no assertion about its color. Excluding it, I have. So, to return to Putnam's example, if it is to have any force, it is not enough for the respective scientists not to include the principles and elements of the other scientists. Putnam's objection requires that the particular theorist assert the exclusion of the elements of the other sciences as part of the essence of the dogs that he or she studies. Otherwise there is no argument among the scientists.

Putnam simply provides his example of Shlomit and draws his conclusion, without giving the argument that leads to that conclusion. I think it fair to construe his argument as follows:

(1) Different sciences give essential descriptions of A's (where A refers to a single natural kind, for example, the natural kind dog).

(2) Inspection of the essential descriptions of A's given by the different sciences shows them to be manifestly diverse.

(3) Therefore, the essential forms that constitute the identity of the descriptions are diverse.

(4) However, the essential forms that constitute the identity of the descriptions are identical (in some sense) to the essential form(s) of the natural kind extra animam (beyond the soul), according to the Thomistic Aristotelian CIT.

(5) Thus from (3) and (4), the essential form(s) of the natural kind extra animam must be diverse since they are identical (in some sense) to diverse essential forms in anima (in the soul).

(6) Therefore from (1) and (5), A's, insofar as they fall under different sciences, do not have unique essences or substantial forms.

(7) Therefore, the identity of the natural kind concept A employed in the different scientific descriptions of A's is not determined by a unique essence or substantial form of A.

(8) Therefore the Thomist position is false, since the Thomist assumes the contradictory opposite of (7).

Here I think it very important to mention a crucial presupposition of Putnam's argument, which I will discuss it at greater length later on, namely, that there are natural kinds that have a certain unity to them. The argument presupposes that there is a single natural kind, even as that natural kind has multiple essential descriptions.

Now each description of A, according to Putnam's Thomist, is supposed in its conceptual content to be identical to a substantial form in the world. Consequently, as we have two nonidentical essential descriptions of the same natural kind A, with each description understood in some sense as excluding the other, the conceptual contents of which are prima facie diverse, the natural kind must have at least two types of essence determined by multiple substantial forms, the evolutionary and the genetic. In order to make a point in the last section of the paper, I want to emphasize here that Putnam's argument is not confined to these two sciences, genetics and evolutionary theory. Presumably it applies just as well to morphology, in which, for instance, the bone structure of a natural kind of dog is analyzed while excluding its genetics or evolutionary history. So there are at least three essential descriptions, and at least three types of essence determined by multiple substantial forms, and so on for any additional sciences that happen to study such a natural kind. Thus, there is no unique essence or substantial form to determine the identity of the concept A, in Putnam's example the concept dog, and subsequently to determine the identity of the term "A" or "dog"; what is essential is relativized to a systematic discourse. Putnam's Shlomit is the poor cousin (on the evolutionary scale!) of Quine's unfortunate cycling mathematician, confused and conflicted of mind over the fact that he is and is not essentially bipedal. (6)

Putnam's objection is not unrelated to his problems with different conceptual schemes and with what he calls "Metaphysical Realism." (7) Putnam objects to metaphysical realists that there are no essences "out there" awaiting discovery. Instead the conceptual scheme of a particular science determines for itself what counts as essential for it. The roots of this position run deep within modern philosophy. Consider first Locke's position that:
 'tis evident, that Men make sorts of Things. For it being different
 Essences alone, that make different Species, 'tis plain, that they
 who make those abstract Ideas, which are the nominal Essences, do
 thereby make the Species, or Sort. (8)

Insofar as the mind aranges congeries of ideas to determine what a substance or natural kind word refers to, objects either do or do not fall under it, depending upon whether those objects have characteristics that bear a resemblance to the ideas constitutive of the nominal essence the mind has formed for itself. Transposing this position from internal mental ideas out to the words of a language does not essentially change the claim. (9) If we say that gold is a yellow metal, then a certain set of worldy objects will fall under it. If we provide a different nominal essence, and say that gold is whatever is soluble in aqua regia, then certain objects in the world will fall under it. But the set of objects that falls under the first nominal essence may not be coextensive with the set of objects that fall under the second; for example, platinum is soluble in aqua regia, but it is not yellow. Indeed the intersection of the two sets may be the null set, for all we know.

More recently, the roots of Putnam's objection can be seen in figures like John Dewey and C. I. Lewis, who reflect upon the character of modern logic against a characterization of the background of the old Aristotelian logic. Lewis writes:
 Traditionally any attribute required for application of a term is
 said to be of the essence of the thing named. It is, of course,
 meaningless to speak of the essence of a thing except relative to
 its being named by a particular term. (10)

And Putnam's thesis that what is essential to a natural kind is determined by what a particular scientific discourse considers essential is foreshadowed in Dewey, when he writes:
 As far as present logical texts still continue to talk about
 essences, properties and accidents as something inherently
 different from one another, they are repeating distinctions that
 once had an ontological meaning and that no longer have it.
 Anything is 'essential' which is indispensable in a given inquiry
 and anything is 'accidental' which is superflous. (11)

To be fair, Putnam thinks that once the science has made unto itself an essence in view of some interest of the scientist, everything else falls into place; it's not just anything goes. (12)

Ian Hacking calls this position Putnam's "Transcendental Nominalism" in order to contrast it with what Hacking describes as a "possibly extreme" form of Kantian transcendental idealism. For Hacking, transcendental idealism is about existence, as it asserts that what exists is ideal or mental, having no existence apart from the mind. Putnam's position, on the other hand, is not about existence but about classification. The sorting of the world that we engage in is a product of our minds, as opposed to the Aristotelian realist who believes that "the world just comes in certain kinds. That is nature's way not man's." (13) So Putnam is a transcendental nominalist. (14) The classifications are products of the mind and do not exist apart from them, but the individuals and their individual properties do exist apart from our classifications. Not everything is a discourse, but essentially everything is.

Thus, the distinct conceptual schemes of the sciences determine distinct essences. But keep in mind that Putnam's own view denies that there are any such things as substantial forms or essential structures intrinsic to the beings studied by the sciences. However, he grants to the Thomist essences out there, in order to show that they are in conflict with our supposed consensus about the modern natural sciences. So it would seem that this position ought to be independent of both the Thomist account and Putnam's conceptual scheme account, in order that it may judge between the two without begging any questions. However, on its face, the consensus just seems to be the application of Putnam's transcendental nominalism to the question of the diversity of sciences. The consensus seems to be entailed by Putnam's transcendental nominalism, and thus not wholly independent of it. Indeed, within the context of the philosophy of biology, Putnam's transcendental nominalism is a forceful expression of just one of the various philosophical approaches to the "species problem"; in particular, his transcendental nominalism appears to lead to a neopragmatist approach to species. (15) Thus, prima facie, it is not obviously entailed by the results of contemporary biological science itself.

Consequently, the task for the Thomist is to argue that the apparent diversity of intensional form in diverse scientific discourses does not entail a diversity of extensional form in the natural kind studied within those discourses, even as he holds on to CIT. Further, if he can show that Putnam's plurality view is not adequate to the practice of the diverse natural sciences, then he will have given evidence that Putnam's account of the diversity of the sciences, consensus or not, is false, and that his transcendental nominalism applied to the sciences ought to be rejected along with it.


Aquinas and the Plurality of Forms. With Putnam's objection in view, suppose we turn now to consider Aquinas's discussion arguing for the unity of substantial form against the pluralists in the medieval debate; I will call Aquinas's view the unity of form (UOF) position. Putnam expresses his argument with a familiar rhetorical trope, namely, that medieval philosophy is so completely bound up with the now thoroughly discredited Aristotelian natural sciences that it should not be taken seriously by informed philosophers of the present day. Whatever failures recent philosophy may suffer from, at least it is more in keeping with the progress of the natural sciences. The contemporary consensus against Aristotelianism that Putnam refers to is best seen against the background of this trope. However, mutatis mutandis, some of the objections Aquinas faced are strikingly similar to Putnam's, despite the vast differences in the state of the natural sciences between the thirteenth century and the present day. The larger context of the medieval plurality of forms debate is a complex philosophical and theological issue that involves such questions as the identity of Christ's body in the tomb, the material conditions necessary for human beatitude (often called the "form of corporeality" (16)), and the immortality of the soul. Nonetheless, the arguments for the pluralists' position that Aquinas faced are straightforwardly philosophical. Here I propose to look only at those aspects relevant to addressing Putnam's objection, one of which involves in particular the background of an Augustinian theme in Aquinas on the relationship of mind to the living activities of the body.

Aquinas dealt with a position very similar to Putnam's objection in question 76, article 3 of the first part of the Summa Theologiae. (17) Consider the terms of the medieval debate as described by Aquinas. The objectors argue that there must be a plurality of substantial forms in a human being because of the diversity of Aristotelian scientific descriptions or definitions under which a human being falls, vegetative, sentient, and rational. Consider in particular this objection that Aquinas cites:
 The Philosopher says in Metaph., viii., that the genus is taken
 from the matter, and the difference from the form. But rational,
 which is the difference constitutive of a man, is taken from the
 intellectual soul; while he is called animal from the fact of
 having a body animated as form to matter by a sensitive soul.
 Therefore the intellectual soul is not essentially the same as the
 sensitive soul in a man. (18)

The background for this objection is the Aristotelian scheme of providing an essential definition of a species in terms of specifying both the genus and the difference that contracts or determines the genus to that kind. The example employed is the oft-cited definition, "a man is a rational animal." Notice that the objection begins with a reflection upon the diversity in how a man is "called" "rational" or "animal," when an essential definition is put forward. Notice also that it does not rest content with the thought that "animal" may be discussed without discussing "rational." It positively excludes "rational" from "animal."

The reason given to explain the diversity of "calling" is a diversity of substantial forms in a human being; presumably each difference of term is mapped "isomorphically" to a distinct reality in the world. (19) Thus the prima facie linguistic duality involved in the definition rational animal is taken to be an argument for a real duality in the thing defined. This argumentative strategy is paralleled in Putnam's coupling of the prima facie diversity of genetics and evolutionary theory with CIT to argue for the plurality of essences or substantial forms he thinks contradicts the Aristotelian position. Each science provides distinct essential descriptions mapped isomorphically by CIT onto distinct substantial forms in the natural kind.

In the background of this medieval dispute are at least two streams of thought. The Aristotelian stream of the objection is unmistakable from the language of definition, genus, species, and difference, as well as the analysis in terms of form and matter. The other stream, however, is the Augustinian insight into the great diversity between animate life as we see it in other animals, and the rational life we know ourselves to possess when we turn within and reflect upon ourselves. In his De trinitate, Augustine had distinguished the mind, the inner man, as the major part of the soul, and as consisting of memory, intellect, and will. But he had also written of the "outer man" that
 anything in our consciousness that we have in common with animals
 is rightly said to be still part of the outer man. It is not just
 the body alone that is to be reckoned as the outer man, but the
 body with its own kind of life attached, which quickens the body's
 structure and all the senses it is equipped with in order to sense
 things outside. (20)

Augustine's reference to the principle that "quickens the body's structure and all the senses" is ambiguous, as it is not clear in him whether it should be taken as a part of the soul or as another soul entirely. It is, after all, the body's "own kind of life attached." But, driven by his own reflections upon what he took to be the proper activities of the body, by contrast to the proper activities of the mind, it is clear for Augustine that the life of the body is to be wholly distinguished from the life of the mind, even if the mind and the quickening principle of the body are two distinct parts of the soul. Thus, at least in this discussion from the De trinitate, there appears to be a real diversity in a man between his rational principle and the principle that quickens the body with its "own kind of life attached."

My reason for focusing upon the ambiguity in Augustine's discussion of mind and soul in the De trinitate is that it is the major source for the objections that animate Aquinas's discussion of mind in question 10 of the De veritate, written a decade earlier than the Summa. (21) Aquinas clearly presupposes UOF throughout his discussion, but he does not explicitly discuss it or even mention it in question 10. (22) Thus there is no question of two formal principles in Aquinas's discussion of mind, one for the life of the mind and the other for the life of the quickened body. But in this earlier discussion, Aquinas did manage to preserve the special character of the Augustinian mind in the Aristotelian language of powers, when he held that the mind was a special "general power" consisting of the particular powers of memory, intellect, and will. This general power has its own special unity over and above the unity it has in the soul with all the other powers of the soul, vegetative and sentient, and thus should be clearly distinguished from the "sensitive" part of the soul. On the other hand, presupposed throughout Aquinas's discussion is that there is only one soul or substantial form of a human being, and the mind is but a part of it.

This distinct life of the mind in the De veritate proved distinctly short lived in Aquinas. He abandons this special character and unity of the Augustinian mind in the Summa Theologiae discussion often referred to as the "Treatise on Human Nature. (23) Though the sources of the underlying philosophical discussion of human nature are dominantly Aristotelian, it is nested within a much larger theological discussion of the Divine Verbum and man as the imago dei. In that larger discussion, as in the De veritate, Augustine's De trinitate is the major background source setting the context of discussion. But no longer are memory, intellect, and will given pride of place as a single general power within the soul; no longer do they have their own special unity apart from and mediating their unity with the other powers in the soul. Instead, all of the powers, sensitive, vegetative, and rational, are hierarchically ordered and united in and by the unity of the one soul itself.

While Aquinas was not concerned with the plurality of forms discussion in the De veritate, in the Summa he clearly is. A thirteenth-century Augustinian opponent could very easily use Aquinas's Aristotelianism against him and argue that if the mind has the special unity and life that Aquinas grants to it in the De veritate, then on Aristotelian grounds it is not sufficient to hold that it is a general power of the soul; it must be another soul entirely. A form of life as distinct as Augustine emphasizes in the De trinitate, and as reflected in Aquinas's efforts to give it its own special unity within the soul in the De veritate, requires a distinctive principle of life, a distinctive soul. The essence of the one soul must be distinct in reality from the essence of the other. This is one way of understanding what is taking place in the objection that Aquinas considers here in the Summa, an Augustinian objection posed in Aristotelian terms, an objection that applies to his own earlier discussion in the De veritate. To resist that move and retain from the De veritate the special character of the mind as a special part of the soul could only be ad hoc.

To his credit, Aquinas rejects the ad hoc position, as he abandons the grounds for the objection. He abandons throughout the discussion his earlier position that the mind has a special unity within the soul that distinguishes it from the unity it shares with all the other powers of the soul. (24) One major goal of the Summa discussion is to maintain that the intellectual principle is none other than the principle of life of the human animal, its substantial form or soul. The term "mind" now refers primarily only to the power of intellect, not to a general power uniting memory, intellect, and will. Secondarily and by analogy, it refers to the entire soul. But there is no discussion at all of any special general power that unites memory, intellect, and will.

Given the rejection of the special character of the mind that Aquinas maintained in the De veritate, what concerns me here are the reasons he gives for rejecting the plurality of substantial forms. Aquinas's first response is to diagnose what he often calls "the error of the Platonists." It is a fallacy that confuses the features of our manner of knowing with the features of the thing known. He writes that:
 From diverse intelligible characteristics or logical intentions,
 which follow upon the mode of understanding, it is not necessary to
 posit a diversity in the natures of things, since reason is able to
 apprehend one and the same thing in diverse ways. (25)

Notice the generality of the point. It is not simply about the plurality of forms debate confined to souls and human nature. It is perfectly general and concerns any movement from the plurality of the ways we understand to a plurality of things understood; and the emphasis is upon the real unity studied in diverse ways.

This is a good but not entirely adequate response, and Aquinas himself treats it that way. The plurality view is fallacious if it rests merely on the diversity of descriptions involved. But Aquinas recognizes that with an additional thesis no fallacy is involved. In this case he considers a metaphysical thesis concerning the function of the soul. He writes, "the opinion [could be] maintained if, as [Plato] held, the soul were united to the body, not as its form, but as its mover." (26) As a mover of the body it must be distinct in some sense from the body. This Platonic possibility focuses upon the function of the soul, rather than on how it is described in diverse discourses, and as such it avoids the fallacy.

Next, Aquinas turns to offer positive arguments for the unity of the soul, and not simply a dialectical defense against the plurality position. He offers three arguments, two of which bear directly on Putnam's objection, mutatis mutandis. The arguments focus upon the formal character of the soul within Aristotelianism, a formal character which Aquinas has just stressed by mentioning, as a distinct contrast, what he takes to be the Platonic position of the soul as the mover of the body. The first argument considers the unity of the object under consideration. The metaphysical function of form is to provide the unity of being present in some object. Aquinas writes:
 Nothing is simply one except through one form, through which the
 thing has being; for a thing is a being and is one from the same
 principle; and so those things which are named from a diversity of
 forms are not one thing simply, as for example a white man. (27)

If something is described through a diversity of forms, it is because it is not absolutely one. But notice the difference between saying that, and saying that any diversity of descriptions involves a diversity of forms; the latter is what Aquinas flatly denies as fallacious. Not every diversity of descriptions involves "naming from a diversity of forms." So Aquinas cannot be taking the diversity of linguistic descriptions at face value as evidence for their formal diversity. Rather, the diversity or identity of forms in a description is judged on the basis of a judgment of the diversity or identity of those forms in things extra animam. Indeed, elsewhere, commenting upon Aristotle's discussion of the semantics of terms, Aquinas makes that very point. He writes:
 the intention of Aristotle is not to assign identity of the concept
 of the soul through a comparison to articulated sound, as namely of
 one articulated sound there should be one concept; ... but he
 intends to assign the identity of concepts of the soul through a
 comparison to things. (28)

Here he is commenting upon Aristotle's De interpretatione, where Aristotle asserts that while vocal utterances differ among human languages, the mental concepts they signify "are the same for all [men]." (29) In that context, Aquinas is determined to maintain that the identity of spoken terms is determined by the mental concepts they are subordinated to, while the concepts themselves have their identity determined by worldly objects. This is not simply a metaphysical claim about the constitution of concepts. It is also an epistemological claim about how we know concepts, as it speaks of determining the identity of concepts by a "comparison" to worldly things.

The epistemological claim follows from the general theses in Aquinas that something is knowable only insofar as it is in act; that a concept is in act only as the knowing of some object; and finally that we primarily know material objects and know our concepts only by a secondary reflection upon them. Thus the formal identity of terms cannot be known apart from the world cognitively engaged by the community that uses those terms. In other words, Aquinas does not begin with language as prima facie clear and distinct in its semantic content and identity, only to ask how it is that language manages to hook up with the world--the question that animates Putnam. He begins with some known aspect of the world and asks whether this or that fragment of language as it functions within the larger context of linguistic usage adequately captures that aspect, (30) Consider "a man" and "a white man." According to Aquinas's initial response, we cannot simply read off of the manifest complexity of the phrase "a white man" that it involves a plurality of forms in things extra animam. Instead, we judge that the description "a white man" involves a diversity of forms because we already know that white is a diverse form from man in things extra animam. (31) Apart from that, we cannot judge the description "white man" to involve any more forms than does "man" alone, or for that matter "white" alone. (32)

So consider the manifest complexity of the phrase "a rational animal." Aquinas argues that "an animal with many souls would not be simply one." (33) But the unity he has in mind here is the unity of the natural kind that Putnam himself presupposes is discussed in diverse scientific discourses. Aquinas writes, "[I]n things composed from matter and form, something is one through the form, and derives both its unity and species (natural kind) from it." (34) In the life of an animal, when we recognize a central unity in its form of life, we recognize a unity that cannot be adequately accounted for on the supposition that there are many essences for its natural kind.

Recall that Putnam grants to the Thomist his essential or substantial forms for the sake of argument. But if we look closely at Aquinas's position, a substantial form is a principle intrinsic to the being under consideration. It is the distinctive structure of the acts appropriate to the natural kind of which the being is a member. Insofar as those acts exhibit a unity of life, they exhibit an intrinsic principle of their unity. A plurality of substantial forms would leave that unity of life unaccounted for, indeed unintelligible. Thus there can be only one substantial form intrinsic to the being, a form that is the principle of unity in diversity among the acts engaged in by that member of the natural kind.

Aquinas's first argument for essential unity then sets the stage for his second argument that focuses directly upon what is involved in providing an essential definition of this unity--as he puts it "from the manner in which one thing is predicated of another." The key contrast is with accidental predication. The example is rational animal: "A man is a rational animal." Think of the contrast he has just mentioned with "a white man," or "a man is a white animal." Aquinas writes, "those things that are derived from different forms are predicated of one another accidentally." (35) A definition by contrast is true to the extent that its parts, genus and difference, are united by the definition in a way that reflects the simple unity of the form in the thing defined. Thus a human being is said to be an animal through some form, a sentient one. Now suppose the human being were said to be rational through another form, and vegetative through yet another form. Then the relations of rational life to sensitive life to vegetative life in a human being would be accidental, no more related one to another than is the relation of being white to being vegetative, sentient, or rational, which is not at all.

On the contrary, for Aquinas a human being is rational, sentient, and vegetative through "one and the same" form. That is why the definition "a man is a rational animal" is both true and necessary. It is not as if we have two or more forms tied together by some metaphysical glue called necessity. Elsewhere Aquinas denies that the soul is itself composed of many subforms tied together in some form by necessity (what I have just called "metaphysical glue"). We have but one simple form, and the necessity involved is the necessity of serf-identity for forms, that is, the transcendental character of being called unity. (36) The formal unity of "rational animal" is indivisible because it has no formal parts. It is impossible for there to be a human being who, lacking the form of animality, retains the form of rationality, or lacking the form of rationality retains the form of animality, precisely because it is one and the same form by which a human being is an animal and is rational. Recall that the setting of the plurality argument holds that a being is a human being through the rational form. So Aquinas writes, "[I]t is necessary for something to be an animal and to be a man through the same form; otherwise no man could truly be an animal in such a way that animal could be essentially predicated of the man." (37) The other direction of analysis is equally true, namely, that no animal could be truly called "rational" in such a way that "rational" could be essentially predicated of the animal.

This argument does not rely upon a bald assertion of unity. The analysis is established and confirmed in many places in Aristotle's work, and in Aquinas's after him. The most obvious case is the movement of the De anima from an analysis of vegetative to sensitive to rational form, as the higher type of form is not joined to the lower by metaphysical glue, but rather the higher form includes the powers of the lower form within its own unity, without containing the lower form as a part. The argument is based upon recognizing in human action that reason does not add on something additional to animate acts that are the same in other animals; rather, rational is the form that animate acts take in human beings that renders them specifically different from the animate acts of other animals. In Aquinas the argument relies primarily upon his emphasis on the unity of human life--in a human being the actuality of being animal just is the actuality of being rational, even though the powers characteristic of such a being may be actually exercised episodically and apart from one another. And even when they are exercised episodically and apart from one another, most often they enter into the constitution of intentional actions that possess a per se unity subordinated to rational goals teleologically determined by the nature of the human soul as the actual life of this kind of body. This unity is by contrast with a per accidens unity. Failure of one of the powers involved in the per se unity of such an intentional act leads to some measure of failure in accomplishing the act as such.

This account is also confirmed by Aquinas's analysis of what it is "to be rational" in question 79, article 8 of the Summa. Rationality is the distinctive form that intellect takes in an animal. (38) A human being is essentially rational because the formal principle of intellect in a human being is the very same form by which the human is an animal. Consequently, while it is comparatively easy to see that in a human, being an animal is not adequately understood until it is understood to be rational, it is often more difficult to see that being rational is not adequately understood until it is understood to be animate or incarnate, the act of an animal. Intellect apart from animality is not rational. Finally, it involves a rejection of Augustine's position stressing the great gulf between the bodily acts of the human animal and the rational acts of the mind.

Definition brings about an enrichment of the form of the subject by the form of the predicate because subject and predicate are different expressions within cognition of the same form extra animam. Here Aquinas's remarks on the transition from the vague universal to the distinct are appropriate. (39) Putnam treats CIT like a synchronic judgment that two trees, for instance, do or do not have the same form. Since the linguistic expressions appear different upon simple reflection, they must not have the same form, just as in observing two trees we may judge that they do not have the same form. The better analogy for Aquinas is the diachronic recognition that the acorn and the oak are the same being, and have the same form, in one moment of its development rudimentary or vague and in the other flourishing or distinct. Simple observation at any particular moment will not tell us this. Rather, we must attend to the genesis of the one from the other in order to recognize that they are really one thing after all, despite the appearance of being one thing and then another distinct thing. It is the same cognitive universal that was once vague that is now distinct, expressed in a concept that has developed over time. The conditions of its subsequent development are driven by the active engagement of the cognitive community with the worldly beings that set the conditions of its formal identity.

Putnam has a static view of concepts, in which a conceptual change requires a change of concepts, a substitution of one for another. For Aquinas, however, a conceptual change may require only that one and the same concept develop and become enriched, an enrichment that tracks the worldly development of the one who employs it. Just as one cannot drive a wedge between the acorn and the oak, neither can one drive a wedge between the subject and the predicate in a definition. Consequently, for Aquinas the fundamental unity among diverse essential descriptions of a natural kind--vegetative, animate, and rational--found in diverse sciences, is based upon their real unity in the form of the natural kind that they all claim to describe.

From this discussion of Aquinas's argument against the pluralists, there are four elements of his argument for the unity of substantial form that I want to bring to the discussion of Putnam's objection. The first element is the presupposition of a single natural kind under discussion. In Aquinas's discussion it is human kind, but it could just as well have been a kind of dog, perhaps the kind including Putnam's dog Shlomit. His discussion is thoroughly general and does not depend upon any specific claims of particular discredited Aristotelian natural sciences. In addition, the language of genus and species in which it is couched may no longer be of much use to logicians, as it was in the medieval period, but it has certainly not been abandoned in the classificatory schemes of modern biology. The second element is the fallacy Aquinas calls the "error of the Platonists," namely, to attribute the features of our act of knowing objects to the objects known. The third element is the metaphysical role that form has for Aquinas, following Aristotle, namely, as an intrinsic principle of unity for ways in which a being in a natural kind acts. The fourth element concerns form as providing the unity amid diversity in the descriptions we provide of those beings that act, and that we study. While Aquinas uses these elements to deal with a particular problem he faces in the thirteenth century, he does not use them in an ad hoc fashion. They are thoroughly general philosophical tools.

The end result of his discussion is to emphasize the real unity of human life as we experience it, despite the diverse ways we describe it. Certainly in looking at human life, we can attend to those aspects of it that we share in common with other animals without attending to the rational aspects of that same human life. However, it would simply be a bad mistake to consider that abstract examination of human life exhaustive, and to proceed positively to exclude those aspects of human life that display rationality from a full and comprehensive view of human life. Conversely, we can attend to those aspects of human life that exhibit rationality, without attending to their animal embodiment. But an account of human life that positively excluded the animal embodiment of rationality in human life from its account would be simply false. But Aquinas's argument against the pluralists goes even further than simply noting that human life has both animal and rational aspects. It recognizes a fundamental unity in human life such that reason is the very form of the animal acts of a human being--that it is what is essential to both the animal and the rational life of a human being, which are one and the same life when considered comprehensively. We distinguish in order to unite. Turning now back to Putnam, we want to ask whether that recognition of essential unity in diversity isn't also the best approach to the phenomenon of the various different sciences that study natural kinds in contemporary science.


Putnam's Presuppositions. I want to begin the response to Putnam by considering three presuppositions of his argument. The first presupposition is a shared language or conceptual scheme prior to the languages of the diverse sciences. Natural kind terms like "dog" must be used univocally across the diverse sciences that Putnam mentions; in particular the concept dog remains the same in the diverse scientific discourses. If there is no such shared discourse employing the same term dog, and the concept does not retain an identity across the diverse sciences, the scientists involved are simply committing a fallacy of equivocation. Putnam's objection attempts to drive a wedge between two terms, the subject term and the predicate term of an essential description--in our example, "dog" and whatever for a particular science would fill in the predicate space of a definitional statement like "a dog is (essentially)--." The diverse sciences address the predicate space and provide, according to Putnam, different candidates to fill it. But in order to argue about what should fill it, in order to have the argument Putnam thinks they have, they must all take the identity of the subject term for granted.

The second presupposition is that there are natural kinds. Putnam is not an idealist about things in the world and their particular features. Objects in the world have their properties or features. The various combinatorial possibilities of the features will determine different sets within which an object falls. For Putnam, the entire set of actual and possible combinations of features is Wittgenstein's Tractarian form, which he says he has come to recognize is not the Thomist's form. (40) His metaphysical point is that no particular subset of this set is in itself privileged over another out there. Thus we are thrown back upon our interests in pursuing various sciences, and how we focus upon different features as essential. Once a science has determined for itself what it will focus in upon, from then on the results it achieves are in effect determined by those features. Consequently, Putnam believes that any claim about the essence of some kind of being is interest-dependent. In a pragmatic vein, and quoting James, he writes "the trail of the human serpent is over all." (41)

Still, to press his argument against the Thomist, he must presuppose that a natural kind with its features is out there. In his example, what is to be counted as essential is interest-dependent, but the result of the counting is foreordained by the natural kind and its features once the interest is in place. Indeed, he presupposes that any particular animal, Shlomit, for example, is a member of a single natural kind. Putnam himself had written in introducing his objection that, "the intuition that a natural kind has a single determinate form (or 'nature' or 'essence') has become problematical." (42) The problem is not that there are many natural kinds with many essences, but, rather, that in any particular case there is one natural kind with many essences. No doubt, he shares this presupposition of a single natural kind with Aquinas. However, this presupposition is not something he is granting to the Thomist for the sake of argument. The consensus of contemporary thought he is relying upon presupposes it, independently of any supposed Aristotelianism, in order to have the argument he attributes to the diverse sciences.

We have already seen that he assumes without analysis or defense that diverse scientists share a common conceptual scheme in virtue of which they can all talk about this single natural kind, a conceptual scheme that must be logically prior to the distinct conceptual schemes of their diverse sciences. Thus the unity and identity of this natural kind cannot be determined within any one of the conceptual schemes of the parties to the dispute, but come to them from without. But the antimetaphysical key to Putnam's argument consists in driving a wedge between the natural kind and its essence(s), just as at the semantic level the key was to drive a wedge between the subject and predicate in a definition.

The driving of this wedge is not so easy, however, as another one of Putnam's examples shows, though Putnam himself does not recognize the problem. He asks us to consider the possibility of a synthetic dog, that is, a dog, not cloned, but synthesized from the appropriate organic chemicals to have, from the point of view of the genetic biologist, the essential DNA. According to Putnam, the geneticist is likely to count the being as a member of the natural kind. But Putnam argues that the "evolutionary biologists would not regard a 'synthetic' dog as a dog at all. From their point of view, such a thing would simply be an artifact of no interest," (43) since it does not have the history of descent necessary or essential to the population that makes up the natural kind. Conversely, if a geneticist finds in a population of dogs an individual with a significantly different genetic structure, he will exclude it from the natural kind, regardless of its history of descent.

However, this "synthetic" example complicates Putnam's objection in ways that he does not anticipate. A closer look at the example shows that for Putnam kind-membership depends upon what the scientists take to be essential to the natural kind. He cannot drive the wedge between natural kinds and essences that he needs for his argument with the Thomist. What does the identity of this natural kind consist in? It would be ironic to say the least if Putnam, given his rejection of "Aristotelian metaphysical fantasies," (44) fell back upon natural kinds conceived of as Platonist abstracta out there. Assuming that he would just as likely reject such Platonist metaphysical fantasies, and having rejected essences out there conceived of in Aristotelian terms, it looks as though the only resource Putnam can rely upon for the identity of the natural kind is the mere extension of the set out there. But if the identity of natural kinds is determined by extension, an extension determined by our interests, (45) it appears that the diverse sciences that Putnam has in mind cannot assume the single natural kind between them required by the dispute that Putnam wants to attribute to them. His synthetic dog example indicates that the extension or identity of the natural kind is, like the essence(s) of the natural kind, determined by the interests of the scientists involved. Insofar as the extension of their respective sets differs by either including or excluding the synthetic dog, the evolutionary theorist and the geneticist are working with different sets, and thus different natural kinds. No difference of essence without a difference of natural kind. The diverse interest-constituted essences provide us with diverse interest-driven identity conditions for the natural kinds. Shlomit then is a member of many natural kinds. But these interest-constituted natural kinds are directly opposed to Putnam's need for the identity of a single natural kind to be prior to each diverse science, so that the scientists can argue about it. They have no genuine argument with one another over the essence of a particular natural kind, if in fact they are not arguing about a particular natural kind.

This second presupposition, then, undermines the validity of Putnam's argument. While Putnam's objection requires that he hold the natural kind fixed and vary the essential descriptions, his new example suggests that on his own terms he cannot do so. If the geneticist and the evolutionary theorist are not talking about the same natural kind of thing when they give their respective accounts of the essence(s) of dogs, Putnam's objection is based upon a fallacy of equivocation on the term "dogs." After all, the Thomist expects to find a plurality of essences among a plurality of different natural kinds of things. The trouble, if there is one, is with a plurality of essences for one kind of thing. Here we recall the central importance of a single natural kind for the Plurality of Forms debate in Aquinas.

Putnam is suggesting that the geneticist and the evolutionary theorist are talking about two different natural kinds. The philosopher sees it that way; but the evolutionary theorist in media res does not, even according to Putnam. Insofar as Putnam the philosopher claims that the geneticist would include the synthetic dog in her set of interest, while the evolutionary biologist would consider it an "artifact of no interest," (46) Putnam suggests that the evolutionary biologist thinks there is only one natural kind determined by his own science, and that the geneticist's set is not a natural kind at all. Hence, a fallacy of equivocation exists among the geneticist, the evolutionary biologist, and the philosopher. To avoid the fallacy of equivocation Putnam would have to hold that the sets must be coextensive, while the essences for this necessarily coextensive set or natural kind differ. However, this "must" applied to the set constituting the natural kind would be little more than a tacit appeal on Putnam's part to what he considers the errors of "Aristotelian essentialism," (47) a "must" that attaches to the natural kind out there. Putnam is forced into an essentialism without essences, so to speak. Thus, even if it is inconsistent with his own conceptual scheme, the presumed consensus view about the sciences that Putnam relies upon to defeat the Thomist must grant to the Thomist this much, the unity of the natural kind apart from our interests. Otherwise, the objection is simply fallacious.

The third presupposition is Putnam's method of reading off the identity of the essential forms involved from the descriptions. We are supposed to be able to tell from simple inspection of the descriptions alone that they are diverse, and that the forms involved, from the Thomistic point of view, must therefore be diverse. This prior clarity and distinctness of our linguistic resources is implicit in Putnam's thesis that it is our interests that are determining what counts as essential for us. And it is explicit in the transition from step (2) to step (3) in the argument I attributed to Putnam. He then makes the transition from step (3) to step (4), when, using CIT, he argues from the diversity of the descriptions to the diversity of things described. (48)

Interpreting present day Aristotelians as trying to answer the question how our language hooks up with the world, Putnam explicitly attributes this method to the Thomist. He writes:
 One might say (if one is a latter-day [Thomist] who has taken
 account of the linguistic turn), that, in a certain sense, the
 metaphysical form of our descriptions needs to be isomorphic to the
 metaphysical form of the object represented, for reference to
 succeed.... Speaking phenomenologically, we see propositions as
 imposing a certain kind of order on the world.... The metaphysical
 structure that our propositions project onto the world is what the
 world would copy in the best case, the case of the most successful
 and most complete reference, or so my 'latter-day [Thomist]' would
 think. (49)

Notice the emphasis upon the set-theoretic notion of "isomorphism." (50) The use of "isomorphism" and the image of propositions "project[ing]" structure onto the world suggest that Putnam continues to saddle the Thomist with Wittgenstein's Tractarian form, despite his disclaimer that he no longer does so. If we change Putnam's use of "metaphysical" to Wittgenstein's "logical," it is this picture of propositions "projecting" logical form that Wittgenstein presents at different points in propositions 2, 3, and 4 of the Tractatus. (51) Proposition 2 establishes for Wittgenstein that the picturing relationship of a representation is one of identity of "logical" form. Proposition 3 establishes the "projective" nature of propositions. Finally, in proposition 4, Wittgenstein connects the "logical" form of proposition 2 with the "project[ive]" nature of propositions of 3 by asserting that "The proposition is a picture of reality. The proposition is a model of the reality, as we think it is." (52) Thus even isomorphism does not seem to be enough to capture the portrait of the Thomist that Putnam would like to paint with the Tractarian brush:
 [T]he strongest line for the [Thomist] to take is to say that what
 enables reference to take place is a matching (mere isomorphism
 doesn't seem to be enough), some kind of a matching between the
 metaphysical structure our propositions project onto the objects
 and the metaphysical structure those objects actually have. (53)

In Putnam's portrait of the Thomist who has taken the linguistic turn, we are to think of the elements of sentences, subjects and predicates, as the domain, the world as the codomain, and formal identity ("metaphysical" if one is Thomistic, and "logical" if Wittgensteinian) as the mapping function. For his Thomist, the reference of our words is most successful and the truth of our statements guaranteed when they find their exact image projected onto reality. (54) If there is logical complexity in the description it must find its exact isomorphic or projective image in some complexity in the thing described. His Thomist proposes to read a metaphysical structure off of his propositions and project it onto nature, the mirror of the mind.

Given these presuppositions, in what follows I will show that on the contrary the Thomistic Aristotelian is not proceeding from language to world, and that Putnam's argument fails in general.


A Good But Not Completely Adequate Response. The movement in Putnam from the diversity of our scientific descriptions to a diversity of things described is a fallacy. It is not the fallacy of equivocation I mentioned earlier. Rather it is the intension-extension fallacy that Aquinas calls the "error of the Platonists." The fallacy moves from a diversity of intensional content in descriptions to a diversity of extension, or, as Aquinas described it in response to the pluralists, "from diverse intelligible characteristics or logical intentions," "to ... a diversity in the natures of things." (55)

Putnam is well aware of the fallacy in other contexts, as it plays a large part in the argument of his famous and widely commented upon paper "The Meaning of 'Meaning'." That paper is the Ur text in Putnam's argument against the supposed built-in, world-involving identity of mental representations. As he puts it there, "the timeworn example of the two terms 'creature with a kidney' and 'creature with a heart' does show that two terms can have the same extension and yet differ in intension." (56) Notice that his example uses descriptions that may well be involved in essential descriptions of the being under consideration in diverse discourses, if we are so interested. But here, according to Putnam, we are not to expect from the descriptions alone an incipient argument between the cardiologist and the nephrologist. To be fair, when Putnam made this point in "The Meaning of 'Meaning'" he was himself a committed metaphysical realist. (57) But the point does not appear to depend upon his now abandoned realism, as later he makes a similar point more implicitly and indirectly in the very paper in which he brings up his multiplicity of essences objection to the Thomist. In "Aristotle After Wittgenstein" he writes:
 If we say that any pair of different sentences describe different
 events, then events themselves begin to look suspiciously like
 ghostly counterparts of sentences. That is, events become things to
 which, on the one hand, we give exactly the same structure as
 sentences, but which, on the other hand, we put out into the world.
 The inventions of such intermediaries is a piece of philosophical
 legerdemain. (58)

With the negative conclusion of this passage we should heartily agree. But notice again that Putnam continues to be animated by the picture of going from the sentences to the world by a "philosophical" projection. He does not, however, consider how this point might apply beyond the structure of events, to his own example of the essential structure of natural kinds and our descriptions of them. The multiple essences of the presumed consensus view he relies upon look to be just other pieces of this invented "philosophical legerdemain."

I think the diagnosis of this problem is a good response to Putnam, but that it is not completely adequate. Putnam could make a plausible defense against the charge of committing the fallacy in this case. He could grant that in general it is a fallacy to proceed from a diversity of intensions to a diversity of extensions. He might add, however, that it is the Thomistic commitment to CIT that avoids the fallacy, and at the same time makes the Thomist subject to his objection. By contrast, in the ordinary case of the fallacy there is no claim involved that there is any sort of identity between the description and the thing described. The diversity of intensions in conjunction with CIT entails the diversity of extensions. That is, after all, the crucial stage of the argument I reconstructed for him in steps (2), (3), and (4). Consequently, in this special case there is no fallacy involved, and his argument appears to go through. Notice the parallel of the point I am making here with the point Aquinas made in his argument against the pluralists, namely, that with the addition of a metaphysical thesis, in the medieval case that the soul moves the body, the error of the Platonists may be avoided. Similarly here, mutatis mutandis, the addition of CIT is the metaphysical thesis that may allow Putnam to avoid the fallacy in his objection.

One result of this concession is that it suggests that everyone, not just the Thomist, but Putnam and those in the scientific consensus he would speak for, must hold some form of CIT. The recent consensus about the sciences is supposed to be an independent phenomenon, the touchstone against which the Thomist is to be judged. If the participants in the presumed consensus do not hold some form of CIT, what nonfallacious reason do they have for holding that a diversity of descriptions (sciences) implies a diversity of things described (essences of a natural kind)? In that case, CIT is not a particularly Thomistic thesis. The only alternative to recognizing some form of CIT would be to give up the claim that it is by a simple reflection upon the diverse essential descriptions of the different sciences that we have come to the consensus view that a natural kind does not have a unique essence. But then we can ask what reason at all anyone has for holding the multiplicity of essences thesis, particularly when we see the difficulties it drives Putnam into in the first presupposition described above.

Putnam could respond in the fashion I just sketched, but it would require that he abandon the general force of his argument. His multiplicity of essences thesis is supposed to be a position coming from outside of Thomism, a consensus driven by reflection upon modern science. Putnam wants to grant the internal consistency of the Thomistic account, and to defeat it as inadequate to the way things are now agreed upon by those reflecting philosophically upon the diversity of scientific practice. But then it is no longer the case that the problem is with the unity of essence position as such, but rather with the joint satisfiability of the two theses, unity of essence and CIT. Thus Putnam faces a dilemma. Either his objection is fallacious, or, since it itself presupposes CIT, it is subject to a Thomistic response that makes clear what the position is. If the Thomist position is not merely consistent, but also better able to account for the phenomena of scientific discourse, then because Putnam shares CIT with the Thomist, we have good reason to hold that Putnam's multiplicity of essence thesis must be false.


A Good and Ultimately Adequate Response. The second side of this dilemma brings me to what I think is the good and adequate response to Putnam's objection. First, as to what the position actually is, in the transition from (2) to (3) the argument requires that we be able to read off by simple inspection the diverse identity of the forms involved in the diverse linguistic expressions; the descriptions are in effect clear and distinct to our simple reflection. But this movement from a grasp of the identity of our concepts in linguistic expression to the world, an expression of the Linguistic Turn as Putnam describes it, and presumably justified by CIT, is in direct opposition to Aquinas's Aristotelianism. Recall Aquinas's denial of any such movement. Aquinas is not at all interested in answering the problem that Putnam wants to force onto the Thomist, namely, the skeptical question about how our language manages to hook up with the world, since he cannot get the question off the ground. Why not? Because we have no purchase on our words apart from their worldly involvement. Indeed, I just argued that Putnam himself must hold some form of CIT. But the direction of analysis in Aquinas proceeds in the opposite direction, from worldly things to the determination of our "projection" onto the essential identity of concepts. Thomists have no reason to abandon this element of Aquinas's thought, as I have argued at length elsewhere. (59)

Putnam could bandage his argument by granting that the Thomist is not going from concepts to things but from things to concepts, that is, by giving up the idea that the Thomist is trying to answer the skeptical question about how our words manage to hook up with the world. Yet he could still charge that since it is a metaphysical identity thesis, the asymmetry of the epistemological movement does not matter. He could assert that the essential diversity of the things themselves, genes, bones, and historical events, must lead to a diversity of essential concepts. So the argument could be recasted as:

(1) If the formal identity of things determines the formal identity of the concepts under which they fall, then essentially diverse things determine diverse concepts.

(2) But the formal identity of things does determine the formal identity of the concepts under which they fall (CIT).

(3) Therefore, essentially diverse things determine diverse concepts. (1 & 2)

(4) But the objects studied in the diverse sciences are essentially diverse.

(5) Therefore the objects studied in the diverse sciences determine diverse concepts, including essential descriptions and definitions. (3 & 4)

(6) Therefore, the essential definitions of objects supplied by the diverse sciences are diverse. (5)

The conclusion of the argument is then that the essential descriptions of the objects supplied by the diverse sciences are diverse.

This possible rescuing of the argument is all well and good. Indeed the Thomist can happily grant the conclusion if it is not entirely general, but restricted to multiple natural kinds. Again, the Thomist expects to find diverse essential definitions among multiple natural kinds. If, however, the conclusion is taken to be entirely general and applies to a single natural kind, the problem is that it now straightforwardly begs the question, when it simply asserts in step (4) the contradictory opposite of what the Thomist denies of a single natural kind. It is not sufficient for Putnam to point out that genes, bones, and historical events are different from one another. He must maintain that the genes, bones, and historical events are essentially diverse, which begs the question. We have already seen that Putnam cannot argue nonfallaciously for that claim simply on the basis of the diversity of the descriptions given by the sciences for the same natural kind. Perhaps there is a nonfallacious argument for it, but Putnam has not given one.

Finally, the argument would no longer have the conclusion that Putnam needs, as it would not conclude to a multiplicity of essences "out there," but a multiplicity of essential descriptions "in here." But so what? Recall that in the medieval pluralist debate Aquinas does not deny that there are prima facie multiple essential descriptions of human life coming from diverse discourses. This diversity of descriptions is no surprise either to Aquinas then or to the Thomist today.

But why could Putnam not just rest content with common sense, the Aristotelian's own ace in the hole, the common sense that Putnam elsewhere expresses a hope to revive and revise without the errors of "Aristotelian essentialism"? (60) Forget all the claims about the developing and coalescing modern scientific consensus that the Thomist must face. Bones just are not the same thing as genes, and neither is identical to historical events and populations.

Well, no. In taking this tack, Putnam would be relying upon an ambiguity in his initial example. It is supposed to cover such things as historical events, genes, and morphology. But no anatomist simply studies bones. No evolutionary biologist simply studies events. And no geneticist simply studies genes. In each case they study kinds, the history of events involving a certain natural kind (dogs), the bones of a certain natural kind (dogs), and the genes of a certain natural kind (dogs). Here we see the importance attached to Putnam's own presupposition that there are natural kinds, and that in a particular case the diverse scientists are studying only one such natural kind. (61) Without reflecting upon it, Putnam is relying upon a deeper unity in the objects of study than is immediately evident when they are simply described as bones, genes, and events. Which bones? Whose genes?

Looking back at his original objection, it is false that the essential descriptions of dogs given by the different sciences are manifestly diverse. Because of the background context, we may no longer feel the need to repeat in each instance that we are talking about the bones of dogs, the events leading to the evolution of dogs, and the genes of dogs. We take the natural kind for granted as tacitly included within the descriptions. And as tacitly included, those descriptions are not diverse, however much they may appear to be. The formal identity and unity of the linguistic expressions involved is to be found in the formal identity and unity of the kind considered in its evolution, genetics, and morphology, the kind tacitly referred to in any particular study. That is one of the points behind the gruesome Aristotelian insight that the hand studied by the anatomist is only called a human hand analogously. It must always be considered with respect to the living whole of which it is an anatomical part. The anatomist never simply studies a hand; he studies a human-hand, so called because of its relation to a certain natural kind, or a dog-paw in relation to a very different kind. But recall that in Aquinas's argument against the pluralists, his emphasis on the unity of the substantial form was designed precisely to account for this unity of the natural kind in both the distinctive activities characteristic of it and our efforts to define it.

The French Thomist Jacques Maritain wrote, "[W]e distinguish in order to unite." (62) Despite the prima facie diversity in the definitional expressions provided by the different sciences and their subdisciplines, which we have now seen is only partial, in any particular case of a natural kind they are formally identical because they express in different ways what is not formally diverse in the thing beyond the mind. Indeed, on a Thomistic theory of truth, that is what the truth of such expressions consists in, namely, that what is understood separately or diversely by the mind is predicated to be one in things, because it is one and the same in those things. The logically complex understanding we possess is true insofar as it is brought to a unity that is adequate to the simple metaphysical unity of the thing understood. In addition, Aquinas explicitly argues concerning the truth that is found in the human soul that:
 The intelligible character of truth consists in the adequacy of
 intellect to thing; but nothing becomes adequate to itself; rather
 adequacy requires distinct things [in order for one to be adequate
 to the other]; hence the intelligible character of truth is first
 found in the intellect when the intellect begins to have something
 proper to itself which is not had beyond the soul, but that
 corresponds to something beyond the soul, between which an adequacy
 of [intellect to thing] can be recognized. (63)

The thing that the intellect has that is "proper to itself" and cannot be found "beyond the soul" is the logical complexity and diversity found in the subject-predicate structure of its judgments, which results from the abstractive nature of the human intellect understanding reality in many separate, partial, and inadequate ways. So, for instance, the Thomist can wholeheartedly agree with Putnam's point about events and the sentences we use to describe them that "if we say that any pair of different sentences describe different events, then events themselves begin to look suspiciously like ghostly counterparts of sentences." (64) But why is Putnam not willing with the Thomist to extend that insight to natural kinds and the sentences (scientific) that we use to describe them? On Putnam's plurality of essences view, do not natural kinds and their essences begin to look suspiciously like "ghostly counterparts" of scientific sentences?

We saw in Aquinas's second argument against the pluralists that what the intellect has that corresponds to reality is the actual unity of subject and predicate found in judgment that is adequate (true) to the real unity of things. The unity of subject and predicate in judgment adequately captures the unity of the thing defined, and is thus true. Aquinas includes among concepts these judgments or "second acts of intellect." (65) They then become developmentally available to the mind as simple elements for further judgments. When it captures a simple unity like the unity of a form, it is essential and necessarily true; when it captures a complex unity like the unity of substance and accident, it is contingently true. Contrary to Putnam's first presupposition, where the adequacy of truth is concerned, no wedge can be driven between subject and predicate. When we engage in the act of defining some scientific object, we are in pursuit of definitions that more and more adequately express the formal unity of the thing defined. So for the Thomist, there is no isomorphism between the logical and linguistic structure of our scientific discourse projected onto the metaphysical structure of the world, as if either the mind were a mirror of nature or nature a mirror of the mind possessing element by element the same structure as our understanding.


Modern Natural Science and the Unity of Essence. At this point, all I have done is indicate what the Thomist's position is, how it differs from Putnam's characterization of it, and why it is consistent. I have argued that the Thomist does not argue from mind to world as Putnam's argument against him requires. I have also argued that the Thomist's account of concepts is developmental, as opposed to the static account presupposed by Putnam. As of yet, I have shown neither that the position is more adequate to, that is, true to the practice of contemporary science, nor that Putnam's position is inadequate. The danger is that we may be left in a standoff with each side asserting itself, for or against a plurality of forms, and begging the question against the other. So in conclusion, I think it worth mentioning the actual practice of contemporary science as a relevant factor in judging between the two positions, even if I do not have space to pursue it at length here.

Whose view is more adequate to the phenomena of contemporary science? I mentioned earlier Putnam's use of the trope about Aristotelian philosophy falling with Aristotelian science. Putnam presents us with a picture in which the sciences, in addition to doing their work of theorizing about phenomena, and attempting to confirm or falsify their theories, are also arguing with each other concerning who among them has got the real essence of the natural kind. For Putnam we "make unto ourselves the species of things" or, with Wittgenstein in the Tractatus, "we make to ourselves pictures of facts," (66) and the "we" depends upon the kind of scientist we are interested in being. On Putnam's view of this argument among evolutionary scientists in particular, it appears that genetic structure, morphological structure, and history of descent are no more related to one another than are being white and being a human being, that is, no more than related per accidens in a living thing. If they were closely related, we would not expect the argument about the essence of natural kinds that Putnam describes, but rather an investigation of the unity underlying their close relation.

It is true that in contemporary philosophy of biology there are arguments about determining the appropriate criteria for biological species, whether it should be taken to be genetic structure, or morphological characteristics, or evolutionary descent, for instance. However, it is not at all clear whether the criteria suggested are intended to be test criteria for species or constitutive criteria for species. (67) More importantly, the different positions taken in these arguments do tend to derive on the part of the participants from a solitary focus upon one among the diverse biological fields. However, the problem they face, if we are to take them seriously as bearing upon constitutive criteria of species rather than test criteria, is accounting for the extraordinary unity displayed in cooperative scientific endeavors that presuppose and integrate these diverse fields. Historical examples of a search for unity amid apparently diverse scientific discourses and phenomena are abundant at the origins of contemporary science, and include thermodynamics and the Kinetic Theory of Matter applied to the Ideal Gas Law, fluid dynamics and the Kinetic Theory applied to Brownian motion, the Quantum Theory of Radiation applied to both black body radiation in thermodynamics and the photoelectric effect in electromagnetism, and, finally, the bearing of the negative result of the Michelson-Morley Interferometer experiment on a number of subdisciplines within physics, all of which were discoveries of underlying unity that revolutionized modern science in the nineteenth and early twentieth centuries. (68)

But the field of paleo-anthropology which bears directly upon Putnam's reference to genetics and evolutionary biology is perhaps the most striking example for my purpose here. Paleo-anthropology employs both questions of morphology and genetic studies in determining the history of human evolutionary descent. (69) A major and hotly disputed question in paleo-anthropology is whether Neandertals were a race of ancient human beings, that is, archaic Homo sapiens falling within the range of variation of human populations and contributing to the human gene pool, or if they represented a distinct and separate species, Homo neanderthalensis, which was displaced by the more recent arrival of Homo sapiens from Africa. In simpler terms, is Homo neanderthalensis an ancestor species of Homo sapiens or, rather, a cousin species? In the last years of their existence, up until about 30,000 years ago, Neandertals coexisted with our human ancestors. Biologists have speculated that there may well have been some interbreeding, and that thus Neandertals ought to be considered among our immediate species ancestors. They share with human beings certain gross morphological characteristics, as for example similar body shape, walking erect, and so on. Still there are significant morphological differences, as for example having a body size approximately "30% larger than an average modern man and of great muscular strength." (70)

However, more recent work involving examining the morphological structure of the nasal cavities of Neandertal skeletons has suggested that Homo neanderthalensis ought rather to be considered a cousin species to Homo sapiens, not an ancestral one. But more striking still is the independent use of genetic sequencing to confirm this judgment. Researchers used the mitochondrial DNA of the fossilized remains of a Neandertal skeleton found in 1856 in Dusseldorf, Germany to extract a DNA sequence. They then compared this sequence to mitochondrial DNA sequences obtained from modern human beings. The result of this genetic study suggests that in fact there was little or no gene sharing in the time of the coexistence between Homo neandertalensis and Homo sapiens. The most recent common ancestral species of the two existed some 550,000 to 690,000 years ago. This latter figure is some 300,000 years prior to the upward bound for the existence of Homo neanderthalensis, and 400,000 to 500,000 years prior to Homo sapiens. Consequently, Homo neanderthalensis cannot be considered a species in the ancestral history of descent of Homo sapiens. We are distant species cousins of a common ancestor.

There is no question that within this discussion we can distinguish distinct biological disciplines and the parts they play. We have a larger discourse, paleo-anthropology, employing distinct biological subdisciplines, morphology and genetics, to determine an evolutionary question about the history of descent. As one would expect in all scientific investigations, the results are subject to criticism, considerations of reproducibility, and confirmation within the disciplines involved. Still, the recognition of the convergence toward the same truth among the disciplines is not taking place within or as a result of any particular subdiscipline. Yet no one involved in the larger discourse questions the presupposition of the discussion, namely, that both the morphology and genetics of a natural kind do bear upon judgments of the evolutionary descent of that natural kind because there is some kind of unity in their diversity. In addition, they all expect as a test of the question that the morphological and genetic results should converge upon one another. In this case, the genetics falsifies one morphological hypothesis and confirms a competing morphological hypothesis. In doing so, the genetics supports a theory change from the older standard theory about the history of descent in a distinct subdiscipline based upon morphology.

If we compare the Thomist position with Putnam's in respect to this example, we see a clear difference. The Thomist looks at that unity in diversity in the practice of the sciences and supposes that there is an intrinsic essential structure being studied in several different ways; in other words, the Thomist can give a philosophically intelligible account of why the genetic study should bear upon the hypotheses of a distinct discourse, morphology, in its bearing upon species classification and descent. Counterfactually, if the results of the two disciplines had not converged, then the Thomist would want an explanation, for example, of why morphological studies say "ancestor species," and genetic studies say "cousin species," the two apparently contradicting one another. Perhaps such an explanation would be forthcoming, but the scientists themselves do not expect such wide divergence when they perform their studies, and they would want an explanation of the conflict.

On Putnam's position, recognizing only extrinsic essentially structured schemes of classification confined within distinct discourses, the result looks at best accidental, and at worst unintelligible. It looks as if the paleo-anthropologist got lucky, since at the level of the subdisciplines being used, the geneticist denies that the morphology has anything to do essentially with the natural kinds involved, and vice versa for the morphologist. Indeed, for Putnam, they exclude the essential relevance of each others' work. This exclusion makes the paleo-anthropologist's whole approach look unintelligible. Counterfactually, if the results from the paleo-anthropological study had not converged, then it looks as if from Putnam's perspective the scientists involved would retreat into their diverse and closed discourses, and ignore the results of the other discipline as if the negative result had never occurred.

The genetic and evolutionary scientists involved do not in fact believe that their results are essentially unrelated one to another. Quite the contrary--they presuppose the essential unity of the object of their work, despite their diverse methods of studying the object. That essential unity makes their cooperation intelligible, while for Putnam it must look like a mistake they have fallen into, as if they had forgotten the argument they were having with one another over the "real essence." Keep in mind that it was precisely to account for the unity in diversity of human life that Aquinas argued for his position on the unity of substantial form and essential structure in the medieval debate. Mutatis mutandis, here the Thomistic position is at a distinct advantage for understanding the actual practice of science, while Putnam's position can find it only happenstance at best and unintelligible at worst. These phenomena of scientific practice provide independent evidence of the superiority of the Thomistic position, as well as reasons for rejecting Putnam's position.

Finally, given the detailed discussion of the analogy of terms within Thomism, the Thomist need not agree straightaway with Putnam's presupposition that any scientific discourse bears upon the essential in a natural kind in only one sense of the term "essential." For Thomists, causal genesis is the paradigm case in which a term may be extended analogously beyond its primary use. In other words, the Thomist believes that a term X can be, and often is analogously extended to, the causes of X; the classic but mundane example is the term "healthy" applied to a human being and to those foods that cause health when consumed by the human being. In the primary sense of the term, the human being is healthy, while the broccoli he eats is called healthy because it is a cause of that health. But of course we do not apply "healthy" in quite the same sense to both, since the health of the human being involves his being alive, while the broccoli's being called healthy as a cause of health requires that it be dead. (71)

Similarly, the Thomist can maintain that in the primary sense of the term, the essence of some animal is an intrinsic principle of being for that thing, determining the unified structure of its acts, and placing it within a natural kind. A plausible candidate for such an intrinsic principle is the genetic structure of the animal; perhaps not, as scientific investigation may in the future discover some principle even more fundamental, one expression of which in an animal is its genetic structure. Even though the mediating features of biological life complicate any simple reduction of evolutionary development to genetic development, evolutionary theorists themselves tend to attribute some causal responsibility for adaptations subject to natural selection to genetic mutations. However, the history of descent of that animal may be called essential in a secondary sense of the term, insofar as it is a causal chain of events that led through natural selection to the existence of that genetic structure.

One benefit of this recognition of analogy in scientific discourse is that it accounts for a background setting within which the various scientists working within different fields can have intelligible discussions with one another about how the results of their investigations bear upon one another, in particular, why evolutionary theorists should take account of the latest results in genetics, and vice versa. No one thinks the doctor is arguing with the patient over the real essence of health, when he instructs his patient to eat more fruits and vegetables because they are healthy. Just as Aquinas had argued about the fundamental unity between rationality and its animal embodiment as it is displayed in human life, and recognized that unity to be essential to the phenomena of human life, so too, if we attend to analogy and the actual practices of contemporary science, we can see the ways in which the various different contemporary sciences provide us with true descriptions of some kind of thing, but descriptions which need to be brought to some kind of essential unity in order to be fully adequate to the phenomena of that kind. In this regard, and employing the taxonomy of monism, pluralism-cum-realism, and neopragmatism analyzed by Phillip Sloan, the Thomist position comes down on the side of pluralism-cum-realism. (72)

My argument here has not been that the issue between the Thomist and Putnam should be settled simply a priori. Instead, it has been that the Thomist position on the unity of form or essence, with the qualifications made about distinct conceptual approaches to some object of investigation, and the use of analogy in sorting through these distinct approaches, is better capable of accounting for the actual goals and practices of scientific understanding as we see it practiced today than is Putnam's transcendental nominalism and neopragmatism, particularly when we leave the realm of one particular science to ask the integral question of how our different scientific approaches to the world cohere with one another, a question we evidently do ask and pursue answers to. Thus, the Thomist can affirm normatively that our interests should reflect and be informed by the way things are, and that we do not "make unto ourselves the species of things." We distinguish in order to unite. For all the differences between the state of the natural sciences in the thirteenth century and today, adequate philosophical reflection upon the unity amid diversity displayed in the lives of the creatures around us, as well as the unity in diversity of the actual practice of natural science, displays the strength of the Thomistic tradition in handling the plurality of forms position, whether it is dressed up in medieval garb or the most up-to-date contemporary transcendental nominalism.

(1) Putnam often refers to Thomistic-Aristotelianism, following the use of John Haldane, to whom he is responding. For ease of use I use "Thomism" and "Thomistic." I also find the term "Thomistic-Aristotelianism" too narrow as implicitly suggesting that Thomism is exhausted by the Aristotelian element within it, however strong the latter may be. See Hilary Putnam, Representation and Reality (Cambridge: MIT Press, 1988), 20 for an example of his typical usage of "Aristotelian."

(2) Hilary Putnam, "Aristotle After Wittgenstein," in Words and Life, ed. James Conant (Cambridge: Harvard University Press, 1995), 63.

(3) Putnam, "Aristotle After Wittgenstein," 74.

(4) Ibid., emphasis added.

(5) Ibid., 74-9.

(6) Willard Van Orman Quine, Word and Object (Cambridge: MIT Press, 1960), 199.

(7) See, for instance, Hilary Putnam, "The Question of Realism," in Words and Life (Cambridge: Harvard University Press, 1995), 303.

(8) John Locke, An Enquiry Concerning Human Understanding (Oxford: Clarendon Press, 1975), bk. 3, chap. 6, no. 35; p. 461. Emphasis in the original.

(9) Ian Hacking has argued that the Linguistic Turn in philosophy does not dissolve the problems of the theory of ideas that animated early modern thought. Instead, he argues, it transposes them from the mind and its internal objects which were called ideas to a social mind embodied in a language and its internal objects which are called words. See Ian Hacking, Why Does Language Matter to Philosophy? (Cambridge: Cambridge University Press, 1975).

(10) An Analysis of Knowledge and Valuation (LaSalle, Ill.: Open Court, 1946), 41. As found in Irving M. Copi, "Essence and Accident," in Naming, Necessity, and Natural Kinds (Ithaca: Cornell University Press, 1977), 181. Copi himself argues against the reduction of the notion of essence to nominal essence.

(11) A Modern Introduction to Logic (London: Methuen, 1961), 138. Also as found in Copi, Naming, 41.

(12) Putnam, "Aristotle After Wittgenstein," 78.

(13) Ian Hacking, Representing and Intervening (Cambridge: Cambridge University Press, 1983), 108-9.

(14) Admittedly, Hacking's classification of transcendentalisms is loose, since one traditional way of cashing out nominalism about natural kinds is through the assertion that natural kinds do not exist except as mental entities. In that case, to the extent that it admits the mind-independent existence of particulars, nominalism just looks like a limited transcendentalism.

(15) For a discussion of the "species problem" that surveys the various different positions on the nature of species, see Phillip R. Sloan, "Reflections on the Species Problem: What Marjorie Grene Can Teach Us About a Perennial Issue," in The Philosophy of Marjorie Grene, ed. Randall E. Auxier and Lewis Edwin Hahn (Chicago: Open Court, 2002). In particular see pp. 229-30, in which Sloan isolates "monistic," "pluralistic," and "neopragmatic" positions on the species problem.

(16) See John F. Wippel, The Metaphysical Thought of Thomas Aquinas (Washington, D.C.: The Catholic University of America Press, 2000), 346-51

(17) The Summa Theologiae discussion is by no means the only place where Aquinas addressed the Plurality of Forms debate. For an exhaustive treatment of the various places where Aquinas addressed it, and how those treatments differ from one another, see Wippel, The Metaphysical Thought, 327-51.

(18) St. Thomas Aquinas, Summa Theologiae (Ottawa: Garden City Press, 1941), I, q. 76, a. 3, obj. 4. My translation.

(19) It will be evident later that the use of "isomorphically" here is taken directly from Putnam's discussion.

(20) St. Augustine, The Trinity, trans. Edmund Hill (New York: New City Press, 1991), bk. 12. chap. 1; p. 322.

(21) See Torrell, who places the composition of the De veritate during the first Parisian regency from 1256-9 and that of the Prima pars of the Summa in 1268 while Aquinas was in Rome. Jean-Pierre Torrell, Aquinas, trans. Robert Royal (Washington, D.C.: The Catholic University of America Press, 1996).

(22) Aquinas held the unity of form position throughout his career, and he relies upon it as presupposed in response elsewhere in the De veritate itself.

(23) ST I, q. 75-89

(24) See my much more extensive analysis of this issue in "Aquinas's Rejection of Mind, Contra Kenny," The Thomist 66 (January 2002): 15-59.

(25) ST I, q. 76, a. 3, ad 4.

(26) ST I, q. 76, a. 3.

(27) Ibid.

(28) St. Thomas Aquinas, Expositio Libri Peryermenias (Rome: Commissio Leonina, 1989), bk. 1, lect. 2, lines 242-8. (In Marietti, bk. 1, lect. 2, no. 21)

(29) Aristotle, De interpretatione 1.16a7 in The Complete Works of Aristotle, ed. Jonathan Barnes (Princeton: Princeton University Press, 1984).

(30) Against the objection that this claim presupposes a fundamentally individualist account of knowledge acquisition and language learning, see my Thomist Realism and the Linguistic Turn (Notre Dame: University of Notre Dame Press, 2003). See also Fregus Kerr, "Aquinas after Wittgenstein," in Mind, Metaphysics, and Value in the Thomistic and Analytical Traditions, ed. John Haldane (Notre Dame: University of Notre Dame Press, 2002).

(31) It is not necessary to take "already" here as a temporal adverb.

(32) See the discussion of this topic in Metaphysics, 7.4.1029bll-1031a14, in The Complete Works of Aristotle and Aquinas, In Metaphysicam Aristotelis Commentaria (Turin: Marietti, 1935), bk. 7, lect. 3-4. The example "white man" is a common one for Aquinas as he simply takes it over from Aristotle, and it appears in almost every discussion of definition and essential unity. It is for him the paradigmatic case of a linguistic phrase that has no definition. This is how Aquinas understands Aristotle's discussion of the "garment" and the "white man" in book 7 of Aristotle's Metaphysics. The imaginative suggestion is made that we substitute a single term, for instance "garment," for the complex phrase "white man" in order to signify the unity that a white man is. Clearly we are to understand "garment" here to be nothing more than a sound or inscription, and not with its ordinary meaning. They might as well have used "jabberwok," or even better "whiteman." The basic idea is to give a single name to what is otherwise referred to by two. Then just as the single term "man" has a definition because it signifies the unity that is a rational animal, "garment" as used here is supposed then to have a definition, as it is a single term signifying the unity that is a white man. And since it is a single term that is taken to be synonymous with the phrase "white man," it seems to follow that "white man" must itself have a definition. And yet, following Aristotle, Aquinas denies this line of argument. Whether we use "garment," "jabberwok," or "whiteman," there is no definition because the unity signified is an accidental one of diverse forms; and it does not matter whether we signify that accidental unity with one sound as in "whiteman" or with two as in "white man." In short, we do not judge the number of distinct forms from the number of distinct words, but the number of distinct words from the number of distinct forms. So not every single word has a definition, since the unity it signifies may be better captured by two or more words.

(33) ST I, q. 76, a. 3.

(34) "[I]n rebus compositis ex materia et forma, per formam est aliquid unum, et unitatem et speciem sortitur," Aquinas, In Metaphysicam Aristotelis Commentaria, bk. 8, lect. 3, no. 1725.

(35) These quotes are from ST I, q. 76, a. 3.

(36) St. Thomas Aquinas, Quaestiones Disputatae De Veritate (Turin: Marietti, 1948), q. 1, a. 5, ad. 16.

(37) Ibid.

(38) ST I, q. 85, a. 3-4, and particularly a. 5.

(39) ST I, q. 85, a. 5: "The human intellect in the first apprehension does not seize on the spot (statim) a perfect cognition of a thing, but in the first place apprehends something of it, namely the quiddity of the thing itself, which is the first and proper object of the intellect, and then it understands the properties, accidents, and encompassing essential relations of the thing. And according to this it is necessary that it compose or divide one apprehension with another, and from one composition or division proceed to another, which is to reason."

(40) "Aristotle After Wittgenstein," 62-3.

(41) Hilary Putnam, The Many Faces of Realism (LaSalle, Ill.: Open Court, 1987), 16.

(42) "Aristotle After Wittgenstein," 74. Emphasis in the original.

(43) Ibid., 77.

(44) My paraphrase of Hilary Putnam, "Sense, Nonsense, and the Senses: An Inquiry into the Powers of the Human Mind," Journal of Philosophy 91, no. 9 (September 1994): 447.

(45) It is fair to ask, given Putnam's desire to deny essential structures in things apart from our interests, by what else could the identity of a natural kind be determined.

(46) "Aristotle After Wittgenstein," 77.

(47) Hilary Putnam, The Threefold Cord: Mind, Body, and World (New York: Columbia University Press, 1999), 5.

(48) See above, p. 6.

(49) "Aristotle After Wittgenstein," 72.

(50) One feature of an isomorphism is that the set-theoretic structure of the domain and all its internal set-theoretic relations are perfectly mirrored in the codomain or target set of the isomorphism, and vice versa. "Isomorphic groups are literally 'same-structured' because they differ only in the names or nature of their elements; all their algebraic properties are identical," Douglas Smith, Maurice Eggen, and Richard St. Andre Monterey, A Transition to Advanced Mathematics (Monterey, Calif.: Brooks/Cole Publishing Company, 1983), 139. For the notions of "onto" and "one-to-one," see 81-3.

(51) Consider these propositions from the Tractatus:

2.1--We make to ourselves pictures of facts.

2.1511--Thus the picture is linked with reality; it reaches up to it.

2.16--In order to be a picture a fact must have something in common with what it pictures.

2.16--In the picture and the pictured there must be something identical in order that the one can be a picture of the other at all.

2.17--What the picture must have in common with reality in order to be able to represent it after its manner-rightly or falsely--is its form of representation.

2.18--What every picture, of whatever form, must have in common with reality in order to be able to represent it at all--rightly or falsely--is the logical form, that is, the form of reality.

3.11--We use the sensibly perceptible sign ... of the proposition as a projection of the possible state of affairs. The method of projection is the thinking of the sense of the proposition.

3.12--The sign through which we project the thought I call the propositional sign. And the proposition is the propositional sign in its projective relation to the world.

Later in 3.144, Wittgenstein adds that "propositions resemble arrows, they have sense." Ludwig Wittgenstein, Tractatus Logico-Philosophicus, trans. C. K. Ogden (London: Routledge and Kegan Paul, 1986), 41, 45.

(52) Ibid., 4.01.

(53) "Aristotle After Wittgenstein," 73. Consider Wittgenstein again:

2.131--The elements of the picture stand, in the picture, for the objects.

2.14--The picture consists in the fact that its elements are combined with one another in a definite way.

2.15--That the elements of the picture are combined with one another in a definite way, represents that the things are so combined with one another.

This connexion of the elements of the picture is called its structure, and the possibility of this structure is called the form of representation of the picture.

2.151--The form of representation is the possibility that the things are combined with one another as are the elements of the picture.

2.1511--Thus the picture is linked with reality; it reaches up to it. Wittgenstein, Tractatus Logico-Philosophicus, 39.

(54) "Onto" is a technical term in the language of set theory and isomorphisms. A function from a domain A to a set B is onto if and only if the range of the function is identical to the set B. See Smith, Eggen, and Monterey, A Transistion to Advanced Mathematics, 81.

(55) ST I, q. 76, a. 3.

(56) Hilary Putnam, "The Meaning of 'Meaning'," in Mind, Language, and Reality (Cambridge: Cambridge University Press, 1975), 218.

(57) Hacking, Representing and Intervening, 75.

(58) "Aristotle After Wittgenstein," 66.

(59) See chaps. 7 and 8 of my Thomist Realism and the Linguistic Turn.

(60) See Putnam, "Sense, Nonsense, and the Senses," 447.

(61) "Kind" is of course a sliding term. In any actual instance the scientist may be operating at a more general or more particular level in studying a gentis, or family, or class, or order, or kingdom, and so forth. "Dog" itself is a broad classification including within itself many subclasses down to what Aristotelians would call the infima species.

(62) The English translation of his French title, Disinguer Pour Unir (Paris: De Brouwer, 1932). Also known as Degrees of Knowledge.

(63) Quaestiones Disputatae de Veritate, q. 1, a. 3: "Veri enim ratio consistit in adaeqatione rei et intellectus; idem autem non adaequatur sibi ipsi, sed aequalitas diversorm est; unde ibi primo invenitur ratio veritatis in intellectu ubi primo intellectus incipit aliquid proprium habere quod res extra animam non habet, sed aliquid ei correspondens, inter quae adaequatio attendi potest."

(64) "Aristotle After Wittengenstein," 66.

(65) In Libros Posteriorum Analyticorum Expositio (Turn: Marietti, 1955), Proem., no. 4.

(66) See footnote 51, especially proposition 2.1.

(67) For a discussion of the difference between "test criteria" and "constitutive criteria," see David Wiggins, Sameness and Substance (Cambridge: Harvard University Press, 1980), 53-4. For a discussion of the controversies over the nature of species, see Philip Kitcher, "Species," in In Mendel's Mirror (Oxford: Oxford University Press, 2003). See also the earlier Ernst Mayr, Systematics and the Origin of Species (New York: Columbia University Press, 1942); and more recently, Marjorie Grene and David Depew, The Philosophy of Biology: An Episodic History (Cambridge: Cambridge University Press, 2004); and Joseph LaPorte, Natural Kinds and Conceptual Change (New York: Cambridge University Press, 2004). Finally, see the very useful summary of the issue in Sloan, "Reflections on the Species Problem," 225-55.

(68) For a discussion both historical and theoretical of these issues, see Paul A. Tipler, Modern Physics (New York: Worth Publishers, 1978).

(69) My discussion here is heavily dependent upon Thomas Lindahl, "Facts and Artifacts of Ancient DNA," Cell 90 (11 July 1997): 1-3, as well as Matthias Krings, Anne Stone, Ralf W. Schmitz et al., "Neandertal DNA Sequences and the Origin of modern Humans," Cell 90 (11 July 1997): 19-30.

(70) Krings et al., "Neandertal DNA Sequences," 25.

(71) See, for instance, ST I q. 13, a, 5.

(72) See Sloan, "Reflections on the Species Problem."

Correspondence to: University of Notre Dame, Department of Philosophy, 309 Malloy Hall, Notre Dame, IN 46556.


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