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A biological objection to constructive empiricism.

Few works in the philosophy of science have produced the interest and commentary that Bas van Fraassen's The Scientific Image has. This work has managed to set up a powerful defense of a version of Empiricism known as 'constructive empiricism', despite the many seemingly irresistible criticisms of empiricism that scientific realists have developed over many years. Perhaps the most striking thesis of constructive empiricism is summarized by van Fraassen as follows:

... I objected to various lines of reasoning which would lead one to scientific

realism. Some of these arguments, however, concerned the acceptance of a

hypothesis or theory as true, on the basis of the evidence that bears it out. I

resisted such inference, arguing in effect that when the theory has implications

about what is not observable, the evidence does not warrant the conclusion that

it is true (van Fraassen [1980] p. 71).

Evidently, van Fraassen holds that, no matter what the evidence, we are never warranted in drawing conclusions about the existence and properties of unobservable entities. We shall refer to this doctrine as 'the Rejection of Unobservables Thesis'.

But what about the many objections realists have raised to the very distinction between observable and unobservable entities?(1) First of all, it needs to be emphasized that by 'observable' van Fraassen means: observable without the aid of instruments or scientific devices. Something that can only be observed by us by means of a microscope is not, in van Fraassen's sense of the term, observable. So what is or is not observable, in this sense, is not dependent upon the present state of technological or scientific development. That something is observable is just a matter of brute fact. Our powers of observation have limits, and these limits are determined by the limitations of our sensory organs and the nature of the process by which observation takes place. Science itself may tell us what is or is not observable; but whether or not something is observable does not depend upon how much science we have.(2)

It is clear, from a study of The Scientific Image, that van Fraassen has developed his constructive empiricism primarily as the result of his studies of physics and, especially, quantum mechanics. (See especially, [1980], Chapter 3, Sections 8 and 9.) But constructive empiricism is not just a view of physics; it encompasses all branches of science, including biology. As such, it is a philosophy of science (and not just a philosophy of quantum physics). So it is reasonable to test van Fraassen's philosophical views by considering biological examples.(3) It is our contention that the Rejection of Unobservables Thesis is not plausible when applied throughout biology.

There is a kind of mite--Histiostoma laboratorium--that, for reasons to be given below, has captured the attention of Drosophila geneticists.(4) These mites are just barely visible to the naked eye: with the right light and the right background, a person can (barely) see one of these organisms as a tiny speck. Since these organisms are visible, they do not fall within the scope of the Rejection of Unobservables Thesis. Still, these organisms are so tiny that people are unable to discern any of the organism's structure with the naked eye. One can see that such an organism can move quite rapidly across a glass plate. How does it do this? How does it get around? Biologists believe that they can answer these questions. By means of a microscope, one can 'see' what appear to be eight leg-like structures that move in ways appropriate to locomotion. These 'legs', if they truly exist and are as they appear to be, are not observable without the aid of some such device as a microscope,(5) and hence are not observable in the sense that is crucial for the constructive empiricist. It follows, by the Rejection of Unobservables Thesis, that one is not warranted by any empirical evidence in concluding that these leg-like structures exist.

It turns out that a scientist trained to do dissections with the aid of a dissection microscope can remove these legs--at least (not to beg any questions) this is what the scientist would claim that she has done, when peering through her microscope she 'sees' that the mite no longer possesses these eight appendages. One could then see, with the naked eye, that the mite no longer changes its position on the glass slide. Indeed, one could then see that the mite falls off the glass slide when the slide is tilted. Of course, one need not terminate one's investigations at this point. There are a great many additional experiments that could be performed with these mites that biologists would regard as providing us with convincing evidence that these legs exist. Suppose, for example, that it is found that when the legs on one side of the mite are removed (according to what the scientist 'sees' through the dissection microscope), the mite continues to move, but in a strange almost circular fashion. Would not such results provide us with additional evidence for the existence of these legs?

One possible stage in the life cycle of this mite is the hypopus stage, which is adapted to dispersal of the organism under harsh conditions (Ashburner [1989], pp. 1206--11). The hypopus is known to 'leap' in the air, up to as much as two inches (Ashburner [1989], pp. 1206). At least, this is how a realist would describe what the hypopus can do. By performing the operation that the realist describes as 'removing the legs', the scientist can bring it about that the hypopus can no longer perform the feat of 'leaping into the air'. Here again, we seem to have additional evidence in support of the hypothesis that these organisms have legs.

The constructive empiricist does not believe in the existence of the mite's legs. But what is she to make of the following experiment? She will observe the biologist placing mites under the dissection microscope and working on them with dissection tools. She will see the biologist removing the mites from the glass slide and then brushing the slide as if she were sweeping what was on the slide into a solution of physiological saline. (Of course, she will believe that there is nothing on the slide to be swept into the solution, since there is nothing observable on the slide.) She will observe this operation being repeated many times until the experimenter is satisfied that a sufficient number have been dissected for the experiment to proceed. The constructive empiricist will then observe the following: The biologist places the solution into a homogenizer, and then pushes the plunger up and down. She will then place the solution into a tube, spin it in a centrifuge and aspirate the solution into a pipet. She will then add it in a centrifuge and aspirate the solution into a pipet. She will then add it to yet another solution, mix the two, and load it onto a gel. The gel is subjected to an electric current, stained and then observed to reveal a pattern of bands characteristic of an enzyme found in animal cells.

The constructive empiricist must ask: If there are no mite legs, what is producing these results that indicate the presence of this enzyme? Do we not have striking evidence of the existence of the legs? Certainly, by such standard accounts of evidence and confirmation as the Bayesian, the results of experiments described above do provide evidence for the existence of these mite legs.(6) If all such results are held by the constructive empiricist not to provide any significant evidence for the existence of these legs, will not biologists begin to wonder just what these philosophers mean by 'evidence'?

The mere appearance of these mites in a Drosophila laboratory creates considerable consternation and activity. For these mites can destroy months of research by killing off whole stocks of fruit flies. These mites can destroy flies quite rapidly. (One can see Drosophila with as many as fifty mites attached to them--before the flies die.) These organisms are believed to feed on yeast and microorganisms (Ashburner [1989], p. 1206). This suggests, of course, that these mites have mouths, or at least something like mouths. Nothing of the sort is 'observable' in the sense relevant to the Rejection of Unobservables Thesis. But under a microscope, a mouth-like structure is plainly visible. Should we maintain, with the constructive empiricist, that belief in these mouth-like structures is not warranted by the available evidence? Few, if any, biologists could accept such a position.

One can place one of these mites near the eye of a small needle and then place this needle under a dissection microscope. Most of these microscopes have 'zoom' capabilities, so that, by simply turning a knob slowly, the magnification is increased continuously. One can, by this procedure, see the mite slowly growing in appearance. By the curvature and shape of the needle, one can determine that what one is looking at is indeed the eye of the needle and the mite. Slowly, the legs and the mouth of the mite will become noticeable. Can one reasonably doubt that these things exist? After all, the theories of optics, light, and vision, used to develop the dissection microscope imply that there is something there which we see by means of the microscope.

Let us suppose, with the constructive empiricists, that the many structural features that our microscopes apparently reveal to us about these tiny organisms that have infested some Drosophila laboratory do not, in fact, exist. In particular, let us suppose that these legs and 'mouths' that these organisms seem to possess when we examine these specks under a microscope do not exist. Supposing that we are one with the constructive empiricists on this score, we would then be unwilling to allow that these tiny things have legs and 'mouths', since they cannot now have what does not now exist. Then, would we take these specks to be mites at all? Are not adult mites eight-legged organisms of the phylum Arthropoda and the class: Arachnida? Do not all adult arachnids have eight walking legs? Imagine the principal researcher of the laboratory, convinced by the philosophical arguments presented by van Fraassen in The Scientific Image, refusing to believe that these tiny things in her laboratory were mites. One can imagine how her colleagues would react if she were not to take action against a mite infestation because of these philosophical beliefs. Would she not be considered absolutely mad by most of her fellow biologists?

Faced with a practical crisis of this sort, her pragmatic nature might come to the fore and prompt her to fight the infestation in the standard fashion, despite her philosophical beliefs. This would involve taking preventative action against hypopi leaping from one culture vial to another. She could then attempt to square her actions with her belief that the specks she sees do not have legs. She could claim that these specks are not mites but that, for some strange reason, they should be treated as if they were mites. Or she could maintain that these specks are genuine mites, but that, contrary to what biologists believe, there are types of mites that are legless and mouthless. Such doctrines, we believe, would not be taken seriously by other biologists.

One rather striking feature of van Fraassen's argumentation in favour of constructive empiricism is its negative emphasis: most of this argumentation consists in refuting various arguments put forth by scientific realists. 'However, there is also a positive argument for constructive empiricism' van Fraassen writes,--'it makes better sense of science, and of scientific activity, than realism does and does so without inflationary metaphysics' (van Fraassen [1980] p. 73). We do not wish to become involved in the very complex question of whether, in general, scientific realism or constructive empiricism makes better sense of science. But it seems very clear to us that, in certain areas of biology, the realistic standpoint makes much better sense of how biologists operate and think than does constructive empiricism. Regarding the sort of situation described above in which thousands of tiny specks appear among the Drosophila, the realist's standpoint seems clearly superior to the constructive empiricist's. As for the claim that constructive empiricism is to be preferred to realism because it 'delivers us from metaphysics' (van Fraassen [1980]), if we restrict ourselves to the sort of biological entities discussed above, then characterizing the 'unobservables' in question as metaphysical entities seems completely misplaced. The word 'metaphysical' is being used by van Fraassen as a pejorative term, connoting something immaterial, insubstantial, transcendental or unearthly. Few, if any, biologists would so characterize the mite legs discussed above.

One reason it seems so implausible to maintain the Rejection of Unobservables Thesis when it is applied to such things as mite legs and 'mouths' is this: our eyesight would not have to improve all that much for the legs and the 'mouths' of these mites to become observable. Indeed, our contemporary theories of light, optics, and vision, can be employed to determine in what respect and how much our eyes would have to be altered to make the legs and mouths visible to us. The situation is, of course, very different when the entities in question are the particles of quantum physics, for it is not at all clear what 'seeing' these particles would consist of.(7) This suggests that it is not the observable-unobservable distinction that is crucial here. The constructive empiricists would do well, we believe, to try to frame their agnosticism about quantum mechanical particles not in terms of the observable-unobservable distinction, but rather in terms of the nature of the entities hypothesized.

(1)See for example Maxwell [1962]. In chapter 1, section 3 of his [1980], van Fraassen responds directly to many of Maxwell's objections.

(2)Mark Wilson delivers a searching and penetrating examination of van Fraassen's views on observability in Wilson [1985]. But cf. van Fraassen's reply in his [1985], on p. 303--5.

(3)This is something Richard Boyd has done in, for example, his [1985].

(4)For a detailed description of this organism, see Ashburner [1989], pp. 1202--13.

(5)'Unaided, the human eye has a resolving power of about 1/10 mm, or 100 micrometers ...Resolving power is a measure of the capacity to distinguish objects from one another; it is the minimum distance that must be between two objects for them to be perceived as separate objects.' (Curtis [1968], p. 94). It is clear that the mite legs being discussed, if they exist, would be much too narrow to be observed without instrumentation. However, for those who feel that the resolving power of the human eye is greater than what is given by Curtis and Barnes, one could give examples of mites that are even tinier than the type given here, or one could focus on parts of the above mite that are much smaller than even its legs and 'mouth'.

(6)There are many Bayesian accounts of evidence and confirmation that will bear this out. See, for example, Rosenkrantz [1977]. See also Chihara [1981].

(7)This was suggested to one of the authors by Bas van Fraassen in conversation.


ASHBURNER, M. [1989]: Drosophila, A Laboratory Handbook. Cold Spring Harbor: Cold Spring Harbor Laboratory Press.

BOYD, R. [1985]: 'Lex Orandi est Lex Credendi'. In Images of Science. Paul Churchland and Clifford Hooker (eds). Chicago: The University of Chicago Press, 3--34.

CHIHARA, C. [1981]: 'Quine and the Confirmational Paradoxes'. In Midwest Studies in Philosophy: The Foundations of Analytic Philosophy, Volume 6. P. French, T. Uehling, Jr., and H. Wettstein (eds). Minneapolis: University of Minnesota Press [1981] 425--52.

CURTIS, HELENA and SUE BARNES, N. [1968]: Biology. Fifth Edition [1989] New York: Worth Publishers Inc.

MASWELL, G. [1962]: 'The Ontological Status of Theoretical Entities'. In Minnesota Studies in the Philosophy of Science, Volume 3. Herbert Feigl and Grover Maxwell (eds). Minneapolis: University of Minnesota Press.

ROSENKRANTZ, R. [1977]: Inference, Method and Decision: Towards a Bayesian Philosophy of Science. Dordrecht: D. Reidel Publishing Company.

VAN FRAASSEN, B. [1980]: The Scientific Image. Oxford: Oxford University Press.

VAN FRAASSEN, B. [1985]: 'Empiricism in the Philosophy of Science'. In Images of Science. Paul Churchland and Clifford Hooker (eds). Chicago: The University of Chicago Press, 245--303.

WILSON, M. [1985]: 'What Can Theory Tell Us about Observation?'. In Images of Science. Paul Churchland and Clifford Hooker (eds). Chicago: The University of Chicago Press, 222--42.
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Author:Chihara, Charles; Chihara, Carol
Publication:The British Journal for the Philosophy of Science
Date:Dec 1, 1993
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