Naturalism and Instrumentalism in the Metaphysics of W. V. Quine

Part 1 of 2

Mar 20, 2025

The philosophical program of naturalism makes two central claims: firstly, the metaphysical claim that the sorts of things studied by the natural sciences are the only sorts of things that exist, and secondly, the epistemological claim that the methods of the natural sciences are the only way to gain knowledge.

The metaphysical position of nominalism denies that there are universals, and advocates limiting the ontological inventory to particulars.

W. V. Quine, in his essay "Natural Kinds", unites nominalism and naturalism. In this essay he attempts to bolster the claims of naturalism by showing how induction, dispositional terms, subjunctive conditionals, and singular causal statements can be accounted for in terms of the notion of kinds, which in turn can be reduced to the theoretical terms of sufficiently developed sciences by way of a nominalistic understanding of the notions of similarity and kinds.

I will here contend that the position Quine takes in "Natural Kinds" is in certain respects at odds with the position he elaborates in his earlier work, "Two Dogmas of Empiricism", and that the latter position is more tenable.

I. From "Two Dogmas" to "Natural Kinds"

The primary focus of this paper is intended to be Quine's metaphysics, but, as with many thinkers, Quine's metaphysical theories cannot be fully understood apart from his epistemological and semantic theories. Accordingly, in this section I will try to present an overview of Quine's metaphysics, epistemology, and semantics, as revealed in four of his best known articles, namely, "Two Dogmas of Empiricism", "Ontological Relativity", "Epistemology Naturalized", and "Natural Kinds".

(D. M. Armstrong notes that Quine does not label himself a nominalist, "on the grounds that he recognizes classes and that these are 'abstract' or 'platonic' entities.")

"Two Dogmas of Empiricism"

The eponymous "Two Dogmas of Empiricism" are the analytic/synthetic distinction and reductionism. Quine denies the existence of "some fundamental cleavage between truths which are analytic, or grounded in meanings independently of matters of fact, and truths which are synthetic, or grounded in fact" (in Martinich, p.39). Quine bases his rejection of this distinction on what he sees as the inadequacy of previous attempts to formulate it.

Kant defines analyticity in terms of the meanings of the subject and predicate of a sentence. If the meaning of the predicate is "contained in" the meaning of the subject, then the sentence is analytic. Quine finds the notion of meaning involved in this formulation problematic, for it seems to make meanings into entities of some sort.

Meaning cannot be the same as naming, Quine says, citing familiar examples from Frege and Russell, as well as Quine's own example of "9" and "the number of planets", to show that the meaning of a singular term cannot be its referent. Similarly, the meaning of a general term cannot be its extension, as Quine's "creature with a heart (kidney)" case shows. Quine concludes that the notion of meanings as entities is mysterious.

The notion of analyticity that Frege and Russell use in their work differs from that of Kant. Frege and Russell deny the existence of the synthetic a priori, collapsing the statements that Kant placed in this category into the category of the analytic. Another difference between the two notions of analyticity is the role played by logical form. For Frege and Russell, analyticity is based on the notions of logical truth and synonymy. Analytic truths are either (a) logical truths (i.e., true in virtue of the logical relationships that obtain between the descriptive words of the statement, not in virtue of the meanings of the descriptive words themselves), or (b) can be transformed into logical truths by substituting synonyms for the descriptive words of the sentence.

This move eliminates the need to postulate meanings as entities. But Quine finds the notion of synonymy almost as problematic as meanings. Synonymy cannot be understood simply as a matter of definition, Quine says, for the lexicographical fact that two words have the same definition is based on an empirical fact about existing usage, namely the fact that the words in question are used synonymously. Definition is based on synonymy, not vice versa. Nor can the synonymy of two words be defined in terms of their interchangeability salva veritate in all contexts, if synonymy is to be used in an explication of analyticity. For while interchangeability can be used to explicate synonymy, explicating it in this way will presuppose an intensional notion of necessity that in turn presupposes analyticity.

Finally, Quine turns to the verification theory of meaning. This theory states that the meaning of a statement is the method of empirically confirming or infirming it, with analytic statements being those that are confirmed no matter what (ibid., p.47). Quine notes that this requires an account of the relationship between a statement and the experiences that confirm or infirm it (48). Empiricists have tried to explain this in terms of the reducibility of meaningful statements into statements about immediate experience. Quine notes that valiant efforts on the part of empiricists to systematize this approach, most notably Carnap's Logischer Aufbau der Welt, have failed, yet empiricists continue to suppose that individual statements can be confirmed or disconfirmed independently of any others.

Quine ties together this dogma of reductionism with the dogma of the analytic/synthetic distinction in this way:

It is obvious that truth in general depends on both language and extralinguistic fact. . . . Thus one is tempted to suppose in general that the truth of a statement is somehow analyzable into a linguistic component and a factual component. Given this supposition, it next seems reasonable that in some statements the factual component should be null; and these are the analytic statements. But for all its a priori reasonableness, a boundary between analytic and synthetic statements simply has not been drawn. . . . (47)
The dogma of reductionism . . . is intimately connected with the other dogma--that there is a cleavage between the analytic and the synthetic. . . . as long as it is taken to be significant in general to speak of the confirmation and infirmation of a statement, it seems significant to speak also of a limiting kind of statement which is vacuously confirmed, ipso facto, come what may; and such a statement is analytic. (49)

Given that, on the linguistic side, the boundary between analytic and synthetic has yet to be clearly drawn, and on the factual side, an explicit theory of empirical confirmation is also lacking, Quine proposes discarding the source of the difficulty, from which both of these dogmas spring, that being the idea that the truth of individual statements has a factual and a linguistic component (49-50).

Quine proposes that the idea of a distinction between a factual and a linguistic component of truth be retained, but not applied to individual statements; rather, "The unit of empirical significance is the whole of science" (49).

Where there are disparities between experience and the predictions of the scientific conceptual scheme, adjustments in that scheme are required, but any and all statements of the scientific belief system are subject to revision. Some statements are more central to this conceptual system than others, meaning that revising certain statements to conform with experience would disrupt the scheme (by entailing further revisions in turn) more than would others. This allows the reconstrual of the analytic/synthetic distinction as a matter of degree rather than a clear categorical distinction; the more central a statement is to the scheme, the more "analytic" it is, with logical truths being the most central of all, though even these are not immune from revision in principle (P. Butchvarov has pointed out the self-defeating nature of this latter claim).

According to Quine, discarding these two dogmas has two consequences of particular importance for empiricism. "One effect of abandoning them is . . . a blurring of the supposed boundary between speculative metaphysics and natural science. Another effect is a shift toward pragmatism" (39).

"Ontological Relativity"

Quine denies that there are meanings "in the head". Quine goes further and says that there are no absolute facts about meaning at all; statements about what a sentence means can only be true relative to a particular schema of translation. In a much later article that I will not examine in detail here, Quine says "the meaning of a sentence of one language is what it shares with its translations in another language" (in Martinich, p.446). By this Quine means to deny what he calls the "myth of the museum":

Uncritical semantics is the myth of a museum in which the exhibits are meanings and words are labels. To switch languages is to change the labels. Now the naturalist's primary objection to this view is not an objection to meanings on account of their being mental entities, though that could be objection enough. The primary objection persists even if we take the labeled exhibits not as mental ideas but as Platonic ideas or even as the denoted concrete objects. Semantics is vitiated by a pernicious mentalism as long as we regard a man's semantics as somehow determinate in his mind beyond what might be implicit in his dispositions to overt behavior. It is the very facts about meaning, not the entities meant, that must be construed in terms of behavior. (Quine, 1969, p.27)

This passage also reveals Quine's primary methodological assumption, namely, linguistic behaviorism. Other methodological premises are the primacy of sentences over words as bearers of meaning, and the necessity of basing translation upon "observational sentences".

The linguistic behaviorism that Quine advocates for this discussion is narrower in scope than either logical or methodological behaviorism. Quine's conclusion does not require the identity of mental states with behavioral dispositions. Quine simply claims that the field linguist, confronted with a case of "radical translation" (that is, a language that the linguist wishes to translate, which has not been translated into any language the linguist knows, and which has no cognates with the linguist's language), has nothing to go on but the observed correlations between "verbal behavior" and the environment. But rather than settling for the underdetermination of meaning-claims based on such evidence, Quine claims that such correlations are all there is to meaning:

. . . the question whether two expressions are alike or unlike in meaning has no determinate answer, known or unknown, except insofar as the answer is settled in principle by people's speech dispositions, known or unknown. (ibid., p.29) The indeterminacy of meaning is a consequence of linguistic behaviorism. But it is not just meaning that is indeterminate; the same considerations lead to the indeterminacy of reference. These considerations apply not only to the translation of unfamiliar languages. They also lead to the conclusion that there is no fact of the matter about whether two speakers of the same language have the same meaning and reference, and indeed the same can be said for a the meaning and reference of a single speaker's use of his language on different occasions. For in all these cases, the observable correlation of behavior with environment is all there is to the matter, and such observations do not entail a single determinate interpretation of the speakers' utterances.

But Quine does not wish to deny that there is a difference between the various interpretations that might be proposed, even though there may be no absolute fact of the matter as to which of the interpretations is the correct one. Quine allows that although there is no absolute difference, there is a relative difference, and consequently a relative fact. In the individual case, there is a fact of the matter about what the individual means relative to a linguistic background apparatus, that is, relative to a network of predicates, auxiliary devices, logical particles, etc. Quine illustrates this by analogy to spatiotemporal relativity: objects can be situated in space only relative to a specified coordinate system (49). The individual can be said to have the same meanings so long as he employs the same linguistic background network within which those meanings are specified relative to each other and to the speaker's behavioral dispositions.

With the individual's system of meanings so defined, a manual of translation can be based on it. Again, the analogy is with spatiotemporal location, with translation functions being analogous to the permutations that equate position in one coordinate system to position in another. The choice of coordinate system or linguistic background network itself is more or less arbitrary.

Quine's linguistic behaviorism would seem to be closely allied to verificationism, and Quine seemed to construe it that way. But Quine's conclusions regarding ontology are not entirely compatible with verificationism. The indeterminacy of meaning implies the denial of the verificationists' claim that ontology is determinately meaningless. The relativity of facts about reference implies the relativity of facts about what there is to be referred to. Ontological discourse is meaningful, and referential, but like any other kind of discourse it is so only relative to an antecedently accepted background network.

"Epistemology Naturalized"

In "Epistemology Naturalized", Quine argues against the traditional conception of epistemology as prior to science, and reconstrues it as being itself a branch of empirical science. In so doing, Quine extends his indeterminacy thesis to scientific theories. Quine bases his arguments on his interpretation of historical developments in the study of the foundations of science and mathematics, and on his understanding of the nature of that inquiry.

Quine divides the study of the foundations of knowledge into conceptual studies, which are concerned with meaning, and doctrinal studies, which are concerned with truth.

The conceptual studies are concerned with clarifying concepts by defining them, some in terms of others. The doctrinal studies are concerned with establishing laws by proving them, some on the basis of others (69-70).

Quine draws a parallel between the logicists' attempted reduction of mathematics to logic, and the empiricists' attempted reduction of empirical science to the terms of sense experience.

Had the logicist program succeeded, it would have provided an ideal case of foundational inquiry, as conceived above. Mathematical knowledge would have been reduced to or derivable from maximally clear and self-evidently true principles of logic. With regard to the foundations of empirical science, Quine traces the progress on the conceptual side of the inquiry, beginning with Hume's identification of bodies with sense impressions. The next big step forward came with Bentham's theory of paraphrasis, or contextual definition, in which it was recognized that the sentence, as opposed to the term, was the "primary vehicle of meaning". This idea was refined in the theories of Frege and Russell, who also broadened the foundations to include logic and set theory in addition to sense impressions. Finally, Carnap attempted to bring this approach to completion, that is, "to account for the world as a logical construct of sense data". But Carnap was unsuccessful, having to settle in the end for relations of implication between science and sense data, rather than outright reduction. The doctrinal inquiry was even less successful. Sentences about immediate sense experience could be taken as self evident, but even if the conceptual program had succeeded, it would not have shown how to derive general laws from singular observation sentences.

So it would seem that the original goal of basing the statements of science on statements of sense experience is unattainable. Quine goes on to say that even the more modest goal of cashing out the meaning of a sentence in terms of its consequences for experience if true, as Peirce suggested, cannot be achieved, because, as Duhem showed, individual statements have no such consequences, though a number of such statements taken collectively will have such consequences.

In other words, theories can be verified, even though theoretical statements cannot. This obviously dovetails with the holism about meaning that Quine advocated in "Two Dogmas" and "Ontological Relativity". Accordingly, Quine extends his indeterminacy thesis from interlinguistic translation to intertheoretic translation. Quine also claims that, despite these setbacks to the empiricist program,

Two cardinal tenets of empiricism remained unassailable, however, and remain so to this day. One is that whatever evidence there is for science is sensory evidence. The other, to which I will recur, is that all inculcation of meanings of words must rest ultimately on sensory evidence (75).

Quine recurs to this latter point when he says,

The sort of meaning that is basic to translation, and to the learning of one's own language, is necessarily empirical meaning and nothing more. . . . Surely one has no choice but to be an empiricist so far as one's theory of linguistic meaning is concerned (81).

In brief, the fact that statements taken in isolation have no empirical consequences leads to both the indeterminacy of translation and the impossibility of reducing theoretical discourse to discourse about sense experience.

Having in effect admitted that the traditional epistemological problems cannot be solved if empiricism is true, rather than doubt the truth of empiricism, or conclude that empiricism leads to skepticism about natural science, Quine chooses to reconstrue epistemology. "Epistemology, or something like it, simply falls into place as a chapter of psychology and hence of natural science" (82). It is the empirical study of the relationship between a human subject, input in the form of sensory data, and output in the form of theoretical discourse. Of particular interest will be the ways in which this output "transcends" the input.

To use a branch of natural science to justify our knowledge claims about science in general would be circular. Quine claims that his view of epistemology avoids this criticism. For Quine claims that epistemology is not concerned with deducing absolutely true theories from observations (that is impossible, for the reasons given above) but is merely concerned with elucidating the relationships between evidence, which must always ultimately be sensory stimulation, and theory.

"Natural Kinds"

Quine begins this essay by reexamining two familiar puzzles: Hempel's puzzle of non-black ravens and Goodman's puzzle of "grue" emeralds. Quine notes that these puzzles can be intuitively solved by recourse to the notion of similarity, or the related notion of kind. But Quine is not content with an unexplicated intuitive notion of kind. The problem Quine sets for himself is to explain, in scientifically acceptable terms (for Quine, that means extensional and non-mental terms), the role that the notion of similarity or kind plays in scientific discourse and methodology, with particular attention to the connection between similarity and induction.

To Quine similarity and kind seem to be "substantially one notion" (119), and notes that although similarity is fundamental to our thought processes, it cannot be reduced to logical or set-theoretical concepts. Quine rejects definition of similarity in terms of properties. One might gloss "a is more similar to b than c" as "a shares more properties with b than with c", but then one would be left with "the unpromising task of what to count as a property" (117).

The nature of what to count as a property can be seen by turning for a moment to set theory. Things are viewed as going together into sets in any and every combination, describable, and indescribable. Any two things are joint members of any number of sets. Certainly then we cannot define "a is more similar to b than c" to mean that a and b belong jointly to more sets than a and c do. If properties are to support this line of definition where sets do not, it must be because properties do not, like sets, take things in every random combination. It must be that properties are shared only by things that are significantly similar. But properties in such a sense are no clearer than kinds. To start with such a notion of property, and define similarity on that basis, is no better than accepting similarity as undefined.
The contrast between properties and sets which I suggested just now must not be confused with the more basic and familiar contrast between properties, as intensional, and sets, as extensional. Properties are intensional in that they may be counted as distinct properties even though wholly coinciding in respect of the things that have them. There is no call to reckon kinds as intensional. Kinds can be seen as sets, determined by their members. It is just that not all sets are kinds. (118)

Induction, Similarity, and Learning

Quine approaches the topic of induction by way of an examination of the importance of similarity to learning, particularly language learning. On Quine's account, one gains acquaintance with certain words like color terms on the basis of ostension, and then through trial and error and the application of a sense of similarity, one learns the proper extension of the word (Quine acknowledges the limits of this account). Quine relies on such examples, and more general examples of learning drawn from behavioral psychology, to support his assertion that a sense of similarity, or "quality spacing", is innate:

Without some such prior spacing of qualities . . . . all stimuli would be equally alike and equally different. These spacings of qualities . . . . can be explored and mapped in the laboratory by experiments in conditioning and extinction. Needed as they are for all learning, these distinctive spacings cannot themselves all be learned; some must be innate. (123)

Quine takes ostensive learning of words to be an example of induction: "Induction itself is essentially only . . . animal expectation or habit formation. And the ostensive learning of words is an implicit case of induction." Quine notes that this sort of induction can be expected to work in language learning, since our quality spacing guides inductions about verbal behavior which is based on the quality spacing of other people, whose quality spacings are presumably like our own.

But what accounts for the success of inductions about nature in general? Quine poses the problem of induction in this way: " . . . why does our innate spacing of qualities accord so well with the functionally relevant groupings in nature as to make our inductions tend to come out right?" (126). Quine proposes a naturalistic solution. Innate quality spacings are presumably transmitted genetically. Successful inductions are conducive to survival, so natural selection favors the transmission of quality spacings that guide successful inductions.

But induction has its failures. Quine also explains this in evolutionary terms. Natural selection would favor quality spacings that facilitate basic animal survival activities like food gathering. But such quality spacings may be of little use to scientific investigation. So evolution must have endowed humans with the ability to "rise above" their innate quality spacings.

This they do by "developing modified systems of kinds, hence modified similarity standards for scientific purposes. By the trial-and-error process of theorizing (they have) regrouped things into new kinds which prove to lend themselves to many inductions better than the old" (128). Thus layers of quality spacings are built up, from the innate to those pertinent to theoretical science, as our "grouping habits" are modified and supplemented.

So, to sum up, Quine links learning, similarity, and induction in this way: learning is linked to quality spacing or sense of similarity because learning requires the drawing of distinctions, which requires a sense of similarity. Learning is linked to induction because learning is habit formation (according to the behaviorism to which Quine subscribed), induction is based on expectation, and expectation is a kind of habit; they are also linked through the process of trial-and-error, which may be seen as both a learning process and as an application of induction. Induction is linked to quality spacing because quality spacings that are in accord with nature are what accounts for the success of induction.

To put it even more briefly: there are natural kinds, our quality spacing corresponds to them, and this is what justifies induction, at least with regard to basic survival activities.

Against the criticism that Quine is using the inductions of evolutionary biology and psychology to justify induction, Quine restates the position he took in "Epistemology Naturalized" regarding the circularity objection.

Similarity and theoretical discourse

Quine goes on to relate similarity to dispositions, subjunctive conditionals, and singular causal statements.

Explaining dispositions in terms of subjunctive conditionals is problematic for empiricists. How can we know that some process would take place if some conditions were met, when those conditions are not in fact met? Using the example of water-solubility, Quine suggests that our conviction in this regard is based on similarity. We believe something will dissolve in water because it is of the same kind(s) as other things that have dissolved in water. More precisely, "a thing is soluble if each kind that is broad enough to embrace all actual victims of solution embraces it too" (130).

Singular causal statements can also be understood in terms of kinds. After noting that Hume's analysis of causes only applies to general causal statements, Quine explains that a particular event causes another event just in case "the two events are of kinds between which there is invariable succession" (132). Quine does not pretend that this is a complete analysis of singular causal statements, but he seems to think he has shown the relevance of kinds to such an analysis.

Quine also believes that the notion of kinds can explicate subjunctive conditionals, though, in a footnote, he notes that his original formulation of this explication was unsatisfactory (131).

So it would seem that the naturalist has a lot at stake with respect to the intelligibility of the similarity notion. Induction, dispositions, singular causal statements, and subjunctive conditionals are all tied to similarity. If similarity cannot be defined in scientifically legitimate terms, then there can be no hope of a scientific explanation of induction--which would mean that the success of science would be scientifically inexplicable. If similarity can be so defined, then dispositions, subjunctive conditionals, and singular causal statements, so long thorns in the side of empiricists, may at last submit to analysis.

What would such a definition look like?

a man's judgments do and should depend on his theory, on his beliefs; but similarity itself, what the man's judgments purport to be judgments of, purports to be an objective relation in the world. It belongs in the subject matter not of our theory of theorizing about the world, but of our theory of the world itself. Such would be the acceptable and reputable sort of similarity concept, if it could be defined. (134)

Quine's solution to this problem draws on his account of the development of the human similarity sense. Quine has noted how this similarity sense progresses from the innate quality spacing, which is geared towards those similarities that are immediately relevant to the survival and reproduction of the individual organism, on up to an advanced similarity spacing that deals with similarities of a cosmic scale. While the innate quality spacing that humans begin life with may not be analyzable, a fully developed similarity sense, the sort that guides the inductions of the most developed sciences, is. Chemistry is such a science:

Comparative similarity of the sort that matters for chemistry can be stated outright in chemical terms, that is, in terms of chemical composition. Molecules will be said to match if they contain atoms of the same elements in the same topological combinations. Then, in principle, we might get at the comparative similarity of objects a and b, by considering how many pairs of matching molecules there are, one molecule from a and one from b each time, and how many unmatching pairs. (135)

Quine goes on to say that while a definition of solubility in terms of chemical similarity can be formulated in this matter, owing to the well-developed understanding of the underlying chemical processes, that same understanding actually makes such a definition superfluous;

One can redefine water-solubility by simply describing the structural conditions of that mechanism. . . . That is, once we can legitimize a disposition term by defining the relevant similarity standard, we are apt to know the mechanism of the disposition, and so by-pass the similarity.

So, natural kinds can be defined in terms of similarity, and similarity can be defined in terms of the underlying processes that science has revealed (or will reveal, in cases where the processes are not as well understood as those of chemistry).

II. Instrumentalism vs. Realism

The philosophical position that Quine develops in these articles possesses, on the whole, an admirable unity. In addition to Quine's unwavering empiricism, the basis for this unity is provided by two theses that appear in all four or these articles, as explicit premises, unstated assumptions, or conclusions. These are (1) the rejection of the priority of philosophy to other sorts of inquiry, and (2) the rejection of the first-person point of view.

Nevertheless, certain of Quine's conclusions are incompatible. This tension can be explored by seeing where Quine stands on the idealism/realism issue in each of these articles. I believe that there is a shift that takes place from a more idealistic position in "Two Dogmas" to successively more realistic positions in the subsequent articles. (I use “realism” here in the sense that is opposed to idealism, and not in the sense that is opposed to nominalism.)

Quine explicitly endorses pragmatism in "Two Dogmas", as has been mentioned. The following passage illustrates this even more clearly:

As an empiricist I continue to think of the conceptual scheme of science as a tool, ultimately, for predicting future experience in the light of past experience. Physical objects are conceptually imported into the situation as convenient intermediaries--not by definition in terms of experience, but simply as irreducible posits comparable, epistemologically, to the gods of Homer. . . . The myth of physical objects is epistemologically superior to most in that it has proved more efficacious than other myths as a device for working a manageable structure into the flux of experience. (in Martinich, 51).

This sort of pragmatism or instrumentalism is an example of what Kant called "problematic idealism", as opposed to "dogmatic idealism". That is, it neither affirms nor denies that there is an external world; it merely views our access to such a world, if it exists, as being problematic. In this spirit, Quine speaks of the concordance between theory and experience, not between theory and the world.

In "Ontological Relativity", Quine maintains this idealism. What there is, or at least what we can speak truly about, depends on our theories. But Quine's behaviorism, or anti-mentalism, which plays no essential role in the argument of "Two Dogmas" (though it perhaps motivates Quine's rejection of meanings as entities), becomes a central premise of the arguments of "Ontological Relativity" and "Epistemology Naturalized", as does the notion of an "observation sentence". These assumptions have realist consequences that become clear in "Epistemology Naturalized", in which Quine begins to move away from this pragmatist/instrumentalist idealism--presumably unwittingly, for Quine explicitly endorses Peirce's version of the verification theory of meaning (albeit not for individual theoretical statements).

Quine's anti-mentalism is indispensable to Quine's defense of his reinterpretation of epistemology:

The stimulation of his sensory receptors is all the evidence anybody has to go on, ultimately, in arriving at his picture of the world. Why not just see how this construction really proceeds? Why not settle for psychology? (75)

Quine raises this point in response to the anticipated objection that his view of epistemology is circular, that is, that it is using science to justify science. But this defense against circularity presupposes a realism about the physiological apparatus of sense experience--Quine talks about sense receptors, not phenomena. This becomes even more explicit in a later passage:

One effect of seeing epistemology in a psychological setting is that it resolves a stubborn old enigma of epistemological priority. Our retinas are irradiated in two dimensions, yet we see things as three-dimensional without conscious inference. Which is to count as observation--the unconscious two-dimensional reception or the conscious three-dimensional apprehension? In the old epistemological context the conscious form had priority, for we were out to justify our knowledge of the external world by rational reconstruction. Awareness ceased to be demanded when we gave up trying to justify our knowledge of the external world by rational reconstruction. What to count as observation now can be settled in terms of the stimulation of sensory receptors, let consciousness fall where it may.

Perhaps Quine might claim that his statements about sensory receptors merely reflect theoretical assumptions which are central to his scheme of beliefs, but which are as open to revision as any others. But if Quine is simply constructing a theory of knowledge, then it is hard to see what differentiates Quine's approach from the rational reconstruction he claims he is abandoning, and therefore it is hard to see how Quine's approach escapes the circularity objection.

Furthermore, another consideration rests upon realism about sensory receptors, namely, the concept of the observation sentence. Quine defines observation sentences in terms of sensory physiology: "an observation sentence is one on which all speakers of the language give the same verdict when given the same concurrent stimulation" (87). Indeed, this would seem to presuppose realism about not only sensory receptors, but other speakers as well.

Quine needs the observation sentence in order to make sense of the verification of theories, including the psychological theories of naturalized epistemology. In so doing he explicitly qualifies the position he took in "Two Dogmas", in which he stated that no individual sentence had empirical consequences of its own:

Sentences higher up in theories have no empirical consequences they can call their own . . . . The observation sentence, situated at the periphery of the body scientific, is the minimal verifiable aggregate; it has an empirical content all its own and wears it on its sleeve. (89)

Now, is Quine's definition of the observation sentence itself an observation sentence? And is sensory stimulation observable? I shall leave these questions to the reader. It seems to me that however they are answered, a consequence will be either that Quine is forced to presuppose realism about sensory physiology (which would entail realism about a lot of other things), or that Quine is constructing a rational reconstruction or theory of knowledge in the traditional sense (which would not escape the circularity objection). The former seems more consonant with the aims of the article in question, so I shall assume that that is what Quine intended.

This perhaps allows Quine to escape the circularity objection, but raises further questions, which by now have become familiar in discussions of "externalist" epistemologies, such as, what kind of epistemic access do we have to facts about the stimulation of our receptors, as opposed to our phenomenal experience? But since the focus of this paper is intended to be on Quine's metaphysics, I shall not pursue this.

In "Natural Kinds", Quine moves even further toward realism. Quine's account of induction presupposes naturalized epistemology, as has been shown, and thus inherits a degree of realism. Furthermore, the connection Quine makes between induction and evolution requires further realism about evolutionary processes and also about the features of external reality that our similarity spacings are keyed to. Perhaps most significantly, Quine's account of similarity in terms of the mechanisms uncovered by science presupposes an even broader realism. If the atoms that Quine refers to in his explication of the similarity that is operative in the concept of water-solubility are merely instruments, then Quine has failed to show that similarity is in any way an objective feature of the world and not a feature of our theorizing; and likewise for the other species of similarity that Quine hopes to account for using this sort of argument. But to count such entities as real is to go beyond what is observationally verifiable, and also attaches empirical consequences to individual theoretical statements.

Thus the position Quine takes in "Epistemology Naturalized" and "Natural Kinds" is at odds with the conclusions of "Two Dogmas" and "Ontological Relativity".

[Due to length, this essay will be concluded in the subsequent post.]

Logos & Liberty

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