It is well-known that Quine argued that the axioms of logic are revisable. The law of the excluded middle, for instance, while at the center of our ‘web of beliefs’ could, if we had compelling evidence, be revised or even abandoned. But it is commonly thought that Quine changed his mind by the time that he wrote his Philosophy of Logic in 1970. But is this right?
What people seem to have in mind is the passage in chapter 6 on deviant logics where he says, in considering the debate between someone who denies the law of non-contradiction and someone who rejects this denial,
My view of this dialogue us that neither party knows what he is talking about. They think they are talking about negation, ‘~’, ‘not’; but surely the notation ceased to be recognizable as negation when they took to regarding some conjunctions of the form ‘p & ~p’ as true, and stopped regarding such sentences as implying all others. Here, evidently, is the deviant logician’s predicament: when he tries to deny the doctrine he only changes the subject. (p 81)
The idea here is supposed to be that it is impossible to really reject the law of non-contradiction as opposed to simply changing the subject. But this doesn’t mean that the law of non-contradiction isn’t revisable, it simply means that arguments between those who are pro-revision and those who are Conservatives will very often be question begging. Quine goes on to say as much when discussing the law of the excluded middle,
By the reasoning of a couple of pages back, whoever denies the law of the excluded middle changes the subject. This is not to say that he is wrong in doing so. In repudiating ‘p or ~p’ he is indeed giving up classical negation, or perhaps alteration, or both; and he may have his reasons. (p 83)
He then goes on to canvass the reasons that have been given, which range “from bad to better”. But ultimately Quine rejects them as sufficient to motivate us to abandon classical logic. He appeals to something he calls the ‘maxim of minimal mutilation’, as he says,
The classical logic of truth functions and quantification is free of paradox, and incidentally is a paragon of clarity, elegance, and efficiency. The paradoxes emerge only with set theory and semantics. Let us try to resolve them within set theory and semantics, and not lay fairer fields to waste. (p 85)
He goes on to cite it again in response to the challenge from quantum mechanics,
But in any event let us not underestimate the price of deviant logic. There is a serious loss of simplicity, especially when the new logic is not even a many-valued truth functional logic. And there is a loss, still more serious, on the score of familiarity. Consider again the case, a page or so back, of begging the question in an attempt to defend classical negation. This only begins to illustrate the handicap of having to think within deviant logic. The price is perhaps not prohibitive, but the returns had better be good. (p 86)
It seems clear from this that Quine is not retracting his claim that classical logic is revisable but is instead canvassing the reasons that one may have for such a revision and arguing that we, as of yet, do not have enough reason to abandon classical logic. This is entirely consistent with his views and so we can conclude that he did not change his mind about the revisability of logic.
2 thoughts on “Did Quine Change his Mind?”
For what it is worth, I agree that Quine didn’t really change his mind about logic’s revisability. Over time, I think Quine began to settle on certain points as best options (e.g. compare “Scope and Language of Science” with “On what there is”) — The posits of science become favored options to be defended against empirically equivalent options, rather than mere mythic constructions on par with their peers. In PHILOSOPHY OF LOGIC Quine can be understood as digging in against nonclassical logics (even in the face of e.g. quantum theory). In both cases overwhelming empirical evidence would still be a basis for theory revision. I disagree with Quine about the revisability of logic, but I dont think he gave up on it as a matter of principle.
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