Carnap’s Program and Quine’s Question
Richard Creath
(Arizona State University)

	The Logical Syntax of Language (Carnap, 1934 and 1937) is an astounding work.  In it and a couple of related papers Carnap develops at least five major innovations.  First, he works out in a rigorous way a metalanguage for talking about linguistic structures.  Second, he develops a viable account of logical consequence.  Tarski said that it was the first generally acceptable one.  It is perfectly consistent with Gődel’s incompleteness results, and to a certain extent it repairs the damage they were thought to do to our ability to deal formally with arithmetic.  Third, it provides a new account of the a priori, or so as not to beg any questions, of the apparent a priori.  Fourth, it gives a new grounding for a robust empiricism, one that is fully in harmony with his account of logical and mathematical knowledge.  Fifth and finally, it presents a new conception of philosophy, one that understands philosophy as what he calls the logic of science.
	As important as they all are, this last is perhaps the most dramatic.  No one who has seen philosophic fashions come and go over many years can be unimpressed with the contrast between traditional philosophy and the empirical sciences.  In the latter we seem to find cooperative efforts, ways of resolving differences of opinion, and fairly durable results.  Even if those results are, of course, fallible, there seems to be real progress amidst the ongoing change.  In traditional philosophy, at least outside logic, we seem to find by contrast only endless wrangles with no plausible way of addressing and resolving them.  Whether these differences between empirical and philosophic work are deep or only superficial, they are still glaring and (to anyone who must admit in public actually to being a philosopher) frustrating.  What Carnap found, or thought he found, in logical syntax was a new way of conceiving of philosophy, a new program for philosophic work, in which the field need not be condemned to this bleak prospect.  No wonder it was controversial.  Its foes denounced it as dangerous, and even its friends seemed not to understand it.
	Perhaps we can do better.  Indeed, the aim of this paper is to get a clearer understanding of what Carnap meant by ‘the logic of science’.  This will allow us to see how dramatic a development it really is, even against the backdrop of Carnap’s earlier work.  If anything, Carnap’s own historical remarks underestimate, and to a certain extent mislocate, the importance of the departure.  It will also allow us to see what kind of resources might be available to meet Quine’s later challenge.  I have no intention here of discussing that challenge in detail; my focus is the logic of science.  But what we learn about the logic of science will have a significant bearing on how the challenge can be addressed.

On the Inadequacies (and Suggestiveness) of Some Histories
	In September of 1935, at one of the last conferences of his European career, Carnap gave a brief talk, “From the Theory of Knowledge to the Logic of Science” (Carnap, 1936) which begins by recounting the main phases of the development of scientific philosophy.  It is a curious history.  The first phase is the overthrow of metaphysics which allows the transition from speculative philosophy to the theory of knowledge.  The second stage is the overthrow of the synthetic a priori, a move which leads to an empiricist theory of knowledge.  The third and then present stage purifies the theory of knowledge of its psychological elements to yield the logic of science.  If this is intended to highlight the characteristic features of his current view, then it both underestimates the magnitude of his own innovation of the syntax period and misleads by directing attention away from the most dramatic and pivotal features of his new philosophy.
	Carnap’s description of the first two historical stages is exceptionally brief, and he gives no explicit indication of what works or authors he has in mind.  But in using the phrase ‘overthrow of metaphysics’ (‘Űberwindung der Metaphysik’) he can hardly be unaware that he used the same phrase in the title of a paper (Carnap, 1932) he published four years earlier.  Presumably he means his reader to make the association as well.  Indeed, if Carnap had meant by the “overthrow” anything substantially prior to the early thirties, there would have been little occasion at that point for a further overthrow through the logical analysis of language or by any other means.  So if by the first historical stage leading to the logic of science Carnap means the struggle against metaphysics waged by himself and his friends in the early thirties, that is before the appearance of Logical Syntax, one would have to note that this campaign is not new, not subtle, and not sustained.  Kant had complained about metaphysics a century and a half before (though there is a certain aspect of the kettle calling the pot metaphysical here).  And for more than a century empirical scientists had objected to metaphysics in noting the increasing irrelevance of professional philosophers to a real knowledge of the world.  In the hands of the logical empiricists themselves the charge of metaphysics had less the delicacy of a dental tool than the roughness of a chain saw.  For Neurath it was a general term of philosophic abuse in which other content may be hard to discern.  Even with Carnap the anti-metaphysical stance seems to embody an empiricism as dogmatic as the anti-empiricism it challenged.  Why should a Heidegger, or for that matter a Russell or a Gődel, take it seriously?  Indeed, before the Principle of Tolerance, how could he defend the Verifiability Principle against the charge that it is self-defeating?  Wittgenstein might smile inscrutably and say “Ah, yes, of course it is nonsense but good and therapeutic nonsense.”  But Carnap could not.
	Of course, Carnap did not maintain the anti-metaphysical stance with its original form and force even to the end of the decade.  In the very early thirties there seem to be absolute standards for the language of science.  Against these standards, metaphysics is absolutely unintelligible.  By “Testability and Meaning” (Carnap, 1936/37), which we may reasonably take as a codicil to Logical Syntax, empiricism is a convention.  It would, thus, seem in principle possible to set up a non-empiricist language whose formation and transformation rules are completely specified.  The expressions of this language would therefore be completely clear and intelligible.  Naturally, the preferred metalanguage for such a language would probably not include a Principle of Tolerance, but that of course is a convention expressed in the metalanguage.  Carnap himself would not have recommended such a non-empiricist language, nor would I.  
	Carnap’s new position including the Principle of Tolerance allows him to sharpen his attack on metaphysics.  He is no more likely to convince metaphysicians to give up their wicked ways.  But he improves his own position internally: clarifying it and showing it to rest, not on dogmatism, but on a reasoned pragmatic choice.  He also makes more precise and fairer his diagnosis of metaphysics.  Such claims are not wholly unintelligible; they are not mere barking.  Rather, as it stands they are sadly in need of clarification, and were they to be clarified, they would not be wrong but unwise and even foolish.  He can portray himself as tolerant and wise and no less firm in his rejection.  By contrast, the metaphysician is portrayed as dogmatic and imprudent.  This sharpening underscores the inadequacy of the original attack.  It underscores as well the inadequacy of Carnap’s historical vignette.  Insofar as Carnap’s remarks are about a stage prior to tolerance, it is not clear that the overthrow really works in philosophic terms.  Insofar as he means to include the syntax stage, he fails to note the very innovation, tolerance, that might make the attack gain some defensible ground.
	Many of these same points can be made about what Carnap calls the second developmental stage of scientific philosophy, the overthrow of the synthetic a priori.  Here again it is difficult to know precisely to what historical episodes Carnap is intending to refer.  But again it does not much matter.  I have no wish to minimize the importance of the change, requiring as it does substantial alterations in Kant’s account of our arithmetic and geometric knowledge.  But we should not over-emphasize it either.  The overthrow was to be carried out by reduction, that is, by deriving the examples of the synthetic a priori such as arithmetic from analytic domains such as logic.  But reducing, in whatever sense, arithmetic or even all of mathematics and geometry to logic, in whatever sense, carries us no closer to empiricism unless we have an empiricist account of logic or else an empiricism that peacefully coexists with it.  Perhaps the latter was achieved with Logical Syntax, but not before.
	Frege seems to have been the first to attempt the reduction of arithmetic to logic, and he was self-conscious about altering certain Kantian doctrines.  But overall he seems to leave the Kantian filing system intact and only to move arithmetic (but not geometry) from the file marked “synthetic” to one marked “analytic”.  The files themselves remain.  His motivation seems not to involve a more fully empiricist epistemology, but precisely to avoid one in mathematics.  His talk of “the logical source of knowledge”, for example in (Frege, 1979, pp. 278f.) makes it hard to see just what his conception of a knowledge of logic would be.  And this does not even mention his reversion in the face of the Russell paradox to the idea that logic must be synthetic a priori after all (Frege, 1979, pp. 267f. and 278-9).
	Russell is said to have actually carried out the reduction of arithmetic to logic.  While his views varied widely over the years, he was generally less sympathetic to Kant than was Frege and often more of an empiricist than either.  Still, his account of our knowledge of logic, and of philosophy more generally, is arguably more platonist than it is anything else
	In the twenties Carnap was a neo-Kantian concerned with the limits of empiricism.  Yet even thereafter but before Logical Syntax, his judgements of analyticity seem absolute.  The question of which logic is correct is apparently assumed to have an answer.  But the correct answer is not provided empirically.  In short, it is far from clear how to fit our logical knowledge into an empiricist framework.  Without that, overthrowing the synthetic a priori would be insufficient to establish an empiricist theory of knowledge.  
	Let us turn then to the third transition, the one that it supposed to represent the current, i.e., mid-thirties, developmental phase of scientific philosophy.  This leads from the theory of knowledge (presumably an empiricist one) to the logic of science and proceeds by purifying the former of its psychological elements.  Philosophers, of course, have shown no reluctance to putting forward psychological theories, but perhaps the scientific interest of those theories is open to debate.  No doubt philosophers are generally ill-equipped to test such theories.  In any case this “purification” would yield a completely formal account, namely, the formal structure of the language of science.  Put in this way, this transition would represent a major departure both from the British tradition of empiricism and from the Kantian philosophy.  Both had tried to describe the operations of the human mind in order to account for our scientific knowledge.  Replacing talk of the structure of the mind with talk of the abstract structure of language is a profound change.  But whether Carnap’s new conception of philosophy, which he calls the logic of science, is adequately represented by equating it with (empiricist) theory of knowledge minus psychology remains to be seen.
	Still the equation is revealing.  A theory of knowledge would presumably include a discussion of justification, both direct and indirect.  Direct justification for an empiricist is nothing but observation.  And sure enough, as both “On Protocol Sentences” (Carnap, 1987, throughout) and hints in Logical Syntax (Carnap, 1937, p. 317) make plain, the “pure” logic that results will specify the observational vocabulary and the structure of observation sentences.  Indirect justification is effected via inference, and the structure of inference is given in logic.  In Syntax the formation and transformation rules in effect define ‘is a sentence’ and ‘is a direct consequence of’ respectively.  From these, a host of other concepts and relations are definable, including the logical consequence relation and analyticity.  ‘Analytic’ is a replacement for the overtly epistemic notion of the a priori, and the consequence relation will later be generalized into the overtly epistemic relations of confirmation and logical probability.  Carnap even hints in Syntax that such a generalization may be possible.  What we have with the logic of science is pure structure, but it is the structure of something epistemic.  True, Carnap generally does not like to put the matter in this way because he thinks that the expression ‘theory of knowledge’ has been preempted by those who are using the term in a psychological way, for example by those concerned with the character of experience.  We need not so use the term in noting the epistemic character of the logic of science.
	Of course, Carnap’s verificationism (better called confirmationism) should itself alert us to the intimate link between epistemic concerns and Carnap’s account of linguistic ones.  Even in the syntax period, Carnap is occasionally very explicit.  In fact, he chose to open “Testability and Meaning” with the following remark:
     Two chief problems of the theory of knowledge are the question of meaning and the question of verification.  The first question asks under what conditions a sentence has meaning, in the sense of cognitive, factual meaning.  The second one asks how we get to know something, how we can find out whether a given sentence is true or false. . . .From the point of view of empiricism,. . . .there is only one answer to the two questions.  If we know what it would be for a given sentence to be found true then we would know what its meaning is.  And if for two sentences the conditions under which we would have to take them as true are the same, then they have the same meaning.  Thus the meaning of a sentence is in a certain sense identical with the way we determine its truth or falsehood; and a sentence has meaning only if such a determination is possible. (p.420, emphasis added)
That the linguistic (syntactic and later semantic) features under study in the logic of science are intended to give us the underlying structure of epistemic relations could hardly be clearer.  It is not called the logic of science for nothing.
	By removing psychology from theory of knowledge, Carnap does transform the philosophic enterprise into linguistic analysis.  That is important, but it is as far as his little history will take us.  Philosophy may be changed, but it is not necessarily improved.  Philosophic disputes are left completely unresolved, and no new avenues of resolution are thereby opened.  Such disputes simply become issues of who has the correct account of the language of science, the correct logic if you prefer.  But we get no help in settling these issues.  Much the same can be said about the account of the apparent a priori.  No doubt it too must be reconstrued as an a linguistic matter, but that is not, by itself, an obvious improvement.  Perhaps the broadly platonistic idea that we have a direct non-observational access to certain features of reality including mathematics and geometry is ruled out by Carnap’s empiricism.  Perhaps Kant’s suggestion that the a priori is a result of the mind imposing form on the matter of experience is likewise foreclosed by the prohibition on psychology.  To preclude these accounts is not to replace them.  We still need a way of addressing disagreements over the structure of the language of science.  It is not that all conflict must cease, but it would be nice to avoid conflict where we can and to understand what kinds of considerations could resolve or at least address the controversies that remain.
	I think Carnap’s syntax program does all this.  That his three developmental stages miss this achievement suggests that they underestimate the magnitude of his departure from traditional philosophy and even mislead the reader by directing attention away from the pivotal point of his program.

Carnap’s Program for Philosophy: Tolerance and the Ersatz A Priori
	As we have seen, even if we overthrow metaphysics and the synthetic a priori, and renounce psychology, and take philosophical problems to be at bottom problems of language, we do not avoid philosophic disagreement.  We just take those disagreements to be over the character of language – language simpliciter or the language of science.  Moreover, we have cut off any means of supporting any side in the disagreement as we cannot appeal to either empirical results or metaphysical insight.  If we are empiricists, we are dogmatic ones.  If we employ a Verifiability Principle, we are in danger of cutting off the branch whereon we sit.  In short, the common caricature of logical empiricism comes very close to being right.  It is not a pretty picture.
	Small wonder then that Carnap was not content to rest there.  Thus, in the “Foreword” to The Logical Syntax of Language Carnap announces a new standpoint:
Up to the present there has been only a very slight deviation, in a few points here and there, from the form of language developed by Russell which has already become classical. . . .The fact that no attempts have been made to venture still further from the classical forms is perhaps due to the widely held opinion that any such deviations must be justified – that is, that the new language form must be proved to be ‘correct’ and to constitute a faithful rendering of ‘the true logic’.
     To eliminate this standpoint, together with the pseudo-problems and wearisome controversies which arise as a result of it, is one of the chief tasks of this book.  In it the view will be maintained that we have in every respect complete liberty with regard to the forms of language; that both the forms of construction for sentences and the rules of transformation (the latter are usually designated as “postulates” and “rules of inference”) may be chosen quite arbitrarily. . . .let any postulates and any rules of inference be chosen quite arbitrarily; then this choice, whatever it may be, will determine what meaning is to be assigned to the fundamental logical symbols.  By this method, also, the conflict between the divergent points of view on the problem of the foundations of mathematics disappears. . . .
     The standpoint which we have suggested – we will call it the Principle of Tolerance . . . – relates not only to mathematics, but to all questions of logic.  (Carnap, 1937, pp. xiv-xv)
This new standpoint profoundly changes the character of philosophy.
	Many philosophic disputes will simply dissolve.  Others can be addressed more fruitfully than before.  The Principle of Tolerance helps in both ways. Claims about language will be about either historically given languages or languages whose structure is specified.  If the former, the question is one of empirical linguistics and thus no longer part of philosophy.  If one wants to do philosophy, the first step is to be clear.  For this one must specify the language one discusses by spelling out its formation and transformation rules (and presumably the observation rules as well).  This standard of clarity is high, but it is attainable as the examples of Carnap and his logician contemporaries make manifest.  These examples also show that it is enormously productive.  These sets of rules are collectively definitions in effect, because they say all there is to say about the features of the language and its expressions.  As definitions they constitute the language.
	Where there is agreement among philosophers about the rules, any residual disputes are appropriately addressed by the usual logical and metalogical techniques.  Where the rules are clearly specified, there are rarely disputes about whether a given demonstration within that system of rules is indeed a demonstration within those rules.  In a way, this vision of philosophy as “calculation” realizes Leibniz’ dream.  Where there are differences in the constitutive rules, we are dealing with different languages.  As claims about different languages, there is no real conflict.  Each philosopher can be right but about a different language.  Nor can there be a claim about which language is the correct one.  As the Principle of Tolerance says:
Everyone is at liberty to build up his own logic, i.e., his own form of language as he wishes.  All that is required of him is that, if he wishes to discuss it, he must state his methods clearly, and give syntactical rules instead of philosophical arguments. (Carnap, 1937, p.52)
Thus, conflicts over philosophic claims may be resolved without recourse to either metaphysical insight or the results of empirical psychology. 
	Each and every claim, of course, is in a particular language.  When a claim is a logical consequence of the structural rules of a particular language, it is in effect a priori, albeit relativized to the language in question.  Carnap calls such claims analytic.  This is not only a relativized a priori, it is also a revisable one.  We can give up one of these claims by abandoning the whole language in which it is embedded.  No Kantian or platonistically inclined philosopher would count the analytic claims as genuinely a priori.  For them the real a priori is neither revisable nor relativized.  Fine.  Carnap avoids the word anyway, preferring, as indicated, the word ‘analytic’.  We can call it the ersatz a priori.  It still serves much the same function; if the language is appropriately constructed, the usual claims of logic, mathematics, set theory, and (mathematical) geometry will still be analytic; and it still forecloses the need for empirical justification.  This choice of language is conventional in the precise sense that it neither has nor needs epistemic justification, that is, reason for thinking that a given choice is the correct or true one.  
	Philosophers will still no doubt differ in recommending or proposing that we adopt different languages.  This is a conflict of a sort, but it is not a difference in claims, for proposals are not claims.  Given tolerance, language choice may be conventional, or epistemically arbitrary, but some languages can still be better than others.  Perhaps none is epistemically better (more likely to be true), but one can certainly be pragmatically better than another.  Some may be simpler or easier to use or more useful in some circumstance.  For example, languages without any inductive rules will be too weak to allow useful predictions about the future, and inconsistent systems are too strong.  In these, at least if the logic is classical, every sentence and its negation will be a theorem.  Hence, the system will completely lose its expectation- and action-guiding power.  What is pragmatically best may vary from situation to situation, and there may be no single best whether in a given context or overall.
	Philosophy is, strictly speaking, an analytic endeavor.  Its claims no more than describe the logical consequences of the constitutive rules of a specific language or of a class thereof.  The philosophic claims themselves do not say that some language system is useful, though of course philosophers will be interested in that topic.  What determines whether a given language system is useful to us may be some feature of ourselves or of the world around us.  Thus, in a very broad and abstract sense, the pragmatic dimension here is quasi-empirical.  The idea is for philosophers to work with scientists to find linguistic structures that the latter can use to describe the world.  Analogously, what makes a given mathematical structure useful to us may be the empirical facts, but the mathematical claims themselves do not describe the facts; they are analytic.
	For the most part, philosophic activity from this standpoint would take language structures specified by their rules and investigate them by logical means.  This would be done for the purpose of estimating their utility in science.  Philosophy becomes a species of conceptual engineering.  Carnap spends a great deal of effort in trying to show that this vision comprises all of the legitimate problems, not only of traditional logic, but also of the methodology of science.  These would include problems of evidence and confirmation, of theoretical reduction, of the conceptual resources of the special sciences, and of space, time, and measurement.  This is more than logic chopping; it is more than playing with words.  It is an enterprise of the utmost intellectual and scientific importance.  Thanks to the Principle of Tolerance, philosophy becomes scientific.  Where the rules have been clearly specified, philosophers can cooperate with one another, either because they are discussing the same set of rules and are jointly investigating its consequences or because the rules are different, the conflict between them has been diffused, and they are now free to compare their results without rancor.  Philosophers can now refocus, as co-workers with scientists, on the overall scientific enterprise.  Gone for good is the pretension of philosophy to be dealing with a domain deeper or higher than that of science.  The dream of a scientific philosophy will have been realized.  
	Under this conception empiricism itself is a proposal (Carnap, 1936/37, p. 33).  And if the proposal is adopted, then synthetic claims will themselves need adequate observational confirmation before incorporation into the fabric of science.  But certain claims about how synthetic sentences can be confirmed will be analytic in the language so adopted.  Indeed, a statement of empiricism itself will be analytic in such a language.  The Verifiability Principle is likewise a proposal, which if adopted would become an analytic metalinguistic sentence about the language thus chosen.  Neither of these would be dogmatic; neither would be self-defeating.  Under this conception, moreover, there is no problem of justifying induction; there is only the serious engineering business of devising rules of inference that are not too weak and not too strong to guide our (probabilistic) expectations.  There are no doubt many ways of doing this, each with different consequences that must be investigated.
	In all of this, the leading idea is the Principle of Tolerance, the idea that there are many languages and none of them is the uniquely correct one.  It allows Carnap to develop an idea of the a priori, albeit one that differs substantially from platonistic and Kantian models.  And it allows him to frame a powerful and defensible program for philosophy.  The endless dogmatic wrangles of philosophy can be addressed and resolved.  And its focus is turned away from “higher”, “deeper”, otherworldly things and toward utility in the overall enterprise of science.  Carnap calls this program the logic of science.  I doubt that it has ever been widely understood or followed.  But it is no less an achievement for all that.

Where to Look for an Answer (to a Question Not Yet Asked) 
	Nearly everyone in philosophy knows that Carnap’s ideas were challenged by Quine, especially in the years 1951-60 (Quine, 1951, 1960a, 1960b).  So it may seem a little odd, in a paper concerned with Carnap’s work in the years 1932-36, to jump ahead and consider Quine.  Certainly there is no opportunity here to go into the details of Quine’s dissent and Carnap’s response.  But even a glance at Quine’s later objection can throw light on the earlier program.  Indeed, what we have learned about that program already, while it will not answer Quine, may suggest some places to look for answers, places that Quine has not adequately canvassed before.
	Specifically, Quine challenges the term ‘analytic’.  It is, he thinks, unintelligible, and were it to be clarified it would not remotely do what Carnap needs to have it do.  The point is vital because Carnap conceives philosophy as an analytic enterprise.  As a technical term ‘analytic’ may seem especially vulnerable to attack, but Quine is happy to agree that it would be perfectly acceptable given the acceptability of any of a large family of other Carnapian notions, including meaning, synonymy, necessity, entailment, and the like.  But Quine thinks they are all infected.  He is in effect rejecting the whole Carnapian program as either unintelligible or as a complete non-starter.  
	To make his charge Quine applies a version of an empiricist criterion of meaningfulness.  He demands more or less what Carnap would have demanded for the descriptive vocabulary of theoretical science, namely one or more correspondence rules linking the theoretical term with the observational circumstances where it is appropriately employed.  Usually Quine expresses this as a demand for behavioral criteria.  By 1960 (Quine, 1960b, Chapter 2) he was emphasizing that such criteria must serve the needs of a field linguist engaging in radical translation, that is, in describing and translating the expressions of an alien language of which we had absolutely no prior knowledge.  Carnap, of course, thought that the demand for correspondence rules and the concern with field linguistics was misplaced because he was explicitly not doing empirical work.  He was investigating artificial languages construed as proposals for the reformation of the language of science.  Though a full response to Carnap would take more time than is available here, Quine’s demand cannot be dismissed so easily.  Even for a proposal, which admittedly does not describe, we must be able to tell, in principle, whether it has been followed; otherwise the proposal is empty.  Telling whether a proposal framed in a theoretical vocabulary has been followed would require something along the lines that Quine demands.  These links to the observational (and in this case behavioral) domain need not be the center of Carnap’s own concerns, but they do need to be available in principle.
	One might well think that, having “purified” philosophy of all hint of psychology to the point that only an abstract formal structure remains, Carnap is not in a very good position to answer Quine.  Indeed, a purely formal structure indicates nothing at all about what its subject matter is, at least nothing beyond some limited information about the cardinality of the domain.  But before we conclude that Carnap’s program is doomed, perhaps we should reflect on what we have learned of it so far.
	One feature of Carnap’s view on which we have just been commenting is that he is not doing empirical work, but rather investigating proposals.  When he says that both logic and mathematics are analytic, he has said nothing about English.  Thus, if satisfactory correspondence rules were provided and used in describing English, it need not turn out that our standard logic or usual mathematics is analytic in that natural language.  Quine often speaks as though, if ‘analytic’ were sufficiently clear, then there would be an unrelativized fact of the matter about whether mathematics, say, is analytic.  Carnap is investigating many languages that differ in their logical structure and in what sentences are counted as analytic.  One supposes, therefore, that Quine must have a specific language in mind, namely English.  Insofar as Quine thinks that Carnap must provide behavioral criteria such that standard mathematics or a given set theory must come out as analytic in English, Quine is surely mistaken, and his demands are unreasonable.
	But are there behavioral criteria at all that would satisfy even the more reasonable demands?  Here we need to appeal to a suggestion from the earlier part of this paper.  It will not give us the criteria, but it might tell us where to look.  In telling us that the logic of science results from theory of knowledge by removing its psychological elements, Carnap was telling us what his formal structures were structures of, namely epistemology.  If one wants to find behavioral correlates of Carnap’s structures, perhaps the place to look is in the epistemic practices of the linguistic community.  We should ask questions like these: How do they argue?  How do they justify their beliefs to one another?  What counts as observational evidence? How strong is that in each case?  What counts as an argument?  How strong is each?  What needs no justification? What patterns do they teach the young?  How in later years do they reinforce these patterns?  How do they correct one another and recognize when correction is appropriate?   These, and questions like them, are not simple observational matters; they concern rather high level social facts.  But they are public and they are fairly near the observational surface.  Neither Quine nor any other serious social scientist thinks that such questions as these are beyond our answering even for a linguistic community that is heretofore completely unknown. 
	Assuming we could (sometimes) get answers to questions like these, it is at least possible that the structure of the answers for a given community would be that of one of Carnap’s constructed languages.  I must say it is unlikely, but it is also unlikely that the structure would be that of Quinean holistic epistemology either.  Even if the community were so radically unlike our own that nothing intelligible could be teased out as answers to questions like the above, that would be beside the point.  Enough in the way of correspondence rules or behavioral criteria would have been provided that in the unlikely event of some community actually following one of Carnap’s proposals, we could, at least in principle, discover that fact.
	If this is suggested in Carnap’s writing, and I think the general outlines are, one may well wonder why Quine himself did not investigate it.  Of course, Carnap did not suggest anything at all about behavioral criteria for analyticity et al. in the 1930s.  And I am not sure that he ever fully understood what Quine was demanding.  Certainly one reason that Quine might have missed the idea that Carnap’s formal structures are structures of epistemology is that Carnap himself speaks so dismissively of the theory of knowledge.  It was too psychological for his taste; he wanted pure structure.  Little did he know that he would later be called on to link those structures to what they were structures of.
	There is a deeper reason, moreover, that Quine would have missed the possibility of tying analyticity and other notions from the theory of meaning to our epistemic practices.  This is because Quine’s own approach to the study of natural language is curiously atomistic, at least in this one respect.  For Quine, if you want to find out whether a given sentence is analytic in a language, you do as follows: Find out if it is analytic for one individual speaker.  No one else is involved at this point.  Then do the same for a second speaker, and so on.  If that sentence is analytic for each person individually, then it is analytic in the language (for example, see Quine, 1974, p. 79).  The same approach is to be used for synonymy, stimulus meaning, and all the other terms from the theories of reference and meaning.
	If Quine took seriously the epistemic dimension of Carnap’s constructed systems, he would most likely have begun again with the individual.  At the outset this would be a matter of a given individual changing his or her beliefs.  Insofar as inference is at issue, this would be something that goes on in the head, away from public view.  Here collateral information (defined and explored in (Quine, 1960b, pp. 37-42)) cannot be recognized.  That is to say that because it is in the head, what is being used as a premise, and hence what the overall patterns of inference are, is not always clear.  Perhaps it never is in such cases.  All of this means that Quine would have missed the social manifestation of epistemic norms.  But that is the level at which we have the most direct observational access.  That is the level at which Carnap’s formal structures can most plausibly be given behavioral criteria.
	Emphatically, I do not claim to have provided here such criteria in detail or even to have proved that they are to be found at the level of public epistemic norms.  But I think this conjecture is a plausible one and one that Quine has clearly not ruled out.  If I am right, and possibly even if I am not, it will turn out that Carnap’s program for philosophy, his conception of the logic of science, is richer, more promising, and more durable than one might have supposed.  That program is more than overthrowing metaphysics and the synthetic a priori, and it is more than separating psychology from philosophy.  Its leading ideas are the Principle of Tolerance and analyticity as a relativized and revisable a priori.  Without these, the other developments were unstable and would have withered.  Carnap proposed the Principle of Tolerance in 1934 to an intolerant world on the brink of universal war.  Today tolerance is still in short supply.  It seems like such a slender reed.  Perhaps, if only in philosophy, it can not only endure but prevail.

Notes