One may not be entirely convinced by John Dewey’s naturalist take on logic.
For example, a primary argument against Dewey’s naturalisation of logic — which won’t be pursued here — is that if the (to use Dewey’s own word) “eternal” truths and principles of logic were really disputable and amendable, then Dewey wouldn’t have even been able to argue this case in the first place. Thus the American philosopher must have — and did — assume and use logical principles and truths (e.g., the law of identity, the law of excluded middle and the law of non-contradiction) which he - and others — questioned and claimed to have a non-absolute status. Of course Dewey might well have assumed and used such logical principles, happily admitted that he did so, and yet still rejected their absolute (or eternal) status.
Having said all that, none of these counter-arguments against Dewey’s thoroughgoing logical naturalism will be advanced in this piece.
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The American philosopher John Dewey (1859 — 1952) clearly had a very particular position on logic. In his eyes, logic should be derived from the methods and practices used in science. And because science is always on the move, then Dewey also believed (as expressed in his Essays on Experimental Logic) that logicians shouldn’t see logical principles as
“eternal truths which have been laid down once and for all as supplying a pattern of reasoning to which all inquiry must conform”.
More generally, Dewey expressed his naturalist position on logic (or at least on “thinking”) in this way:
“[T]hinking, or knowledge-getting, is far from being the armchair thing it is often supposed to be. The reason it is not an armchair thing is that it is not an event going on exclusively within the cortex or the cortex and vocal organs. It involves the explorations by which relevant data are procured and the physical analyses by which they are refined and made precise.”
Thus Dewey believed that just as science doesn’t offer us eternal (or absolute) truths, neither should logic. Indeed if one accepts that logic should — and sometimes does — base its principles on the methods and reasonings found in science, then this attitude to logic will evidently make at least some sense.
There’s another point about logic that’s worth making here.
Platonic Logic?
As with mathematics, even if logic does have eternal principles and truths which somehow exist mind-independently in an abstract realm, it doesn’t at all follow that logicians and mathematicians — any logicians and mathematicians — have unadulterated access to them. Perhaps most logicians and mathematicians simply haven’t discovered (or arrived at) all — or even any — of these eternal principles and truths. So, yes, we may — or can — accept that logic and maths should be beholden to this eternal mind-independent realm. However, it may not be the case that logicians and mathematicians are fully in tune — or in tune at all — with the principles or truths within it. Having said all that, logicians and mathematicians may still have good reasons for believing in this Platonic world’s existence — even if they know little about it.
That said, the use of the word “truth” within a purely logical context is problematic. Many philosophers — including Wittgenstein — have argued that “truth” isn’t the correct word to use when it comes to logical principles, rules, inferences, etc. Instead, thinking in terms of correctness is a better way of looking at these things.
All this means that it would simply be unwise to accept logical principles (or truths) as having some kind of eternal (or absolute) status. Such principles (or truths) may well exist; though logicians may not have access to them in all their fullness. Thus having an absolutist position on logical truths (or principles) may prove to have very negative implications for logic itself and for all those disciplines that (self-consciously) use logic.
Naturalism
It was primarily Dewey’s scepticism about eternal (or absolute) logical truths and principles which made him decide that logicians should base their principles, methods, inferential patterns, etc. on what actually happens in science. That way logicians wouldn’t stick so rigidly to what they believe is the correct (or true) logic. In other words, logic should be fallibilist — just like science. Indeed philosophers like W.V.O. Quine (in the mid-20th century) were fallibilists when it came to both mathematics and logic. Moreover, Quine even became a pragmatist about the Law of Excluded Middle (or at least its applicability) in response to the findings of quantum mechanics and the results of various experiments (see here). In addition, many philosophers believed that statements about the future (i.e., future contingents) can be neither true nor false. Such philosophers, therefore, rejected the Principle of Bivalence. Thus, in this case at the least, logic must include a third value — indeterminate. (See three-valued logic.)
It can now also be argued that certain scientists had rejected the Law of Excluded Middle and the Principle of Bivalence long before most philosophers and logicians had rejected them. And they did so because of science’s relation to the world — or at least science’s relation to “empirical reality”.
On a naturalist (or empiricist) position on logic, the ultimate relation is from the world to logic, not from logic to the world. On the other hand, if logic has no necessary relation to the empirical world (a position that can be called logical Platonism), then logicians may as well stick with their (absolute) principles and truths… for all time. This means that — to such logicians — there may never be any reason to reject these eternal logical principles and truths. Yet what if the world can (as it were) challenge these logical principles and truths? Indeed the world (or at least 20th-century science) has challenged at least some of the assumptions and presuppositions of logic.
Not only is the relation (so Dewey indirectly argued) from the world to logic: the other relation should be from science to logic. In that case, logic seems to take a back seat when it comes to science (or, more usually, physics). And this isn’t so strange if one considers (say) Quine’s additional positions on epistemology, ontology and all the other branches of philosophy. These too, according to Quine, should take a back seat to science. More specifically, Quine argued that there is no— or there shouldn’t be an— a priori epistemology (or an a priori philosophy generally). Therefore there is no fully a priori logic either. So, on a Quinian reading, logic is effectively no different to epistemology in these respects.
And because science’s relation to the world is both more (as it were) direct than logic’s and philosophy’s, then of course the latter (to use Quine’s words) “should defer to science”. Alternatively and to use a term used in the 20th century, logic and philosophy should be naturalised so that they don’t systematically conflict with science and its findings.
So now what about (naturalist) holism?
Most naturalists argue that because single statements, terms, judgements, concepts, etc. aren’t self-sufficient or “atomic”, then neither are the whole disciplines of philosophy and logic. Thus holism - of some description - goes all the way down the line.
To get back to John Dewey’s position on logic and to sum up.
Dewey took a typically pragmatist line on logic. He noted the many successes of science. He therefore believed that whichever logical rules or principles science used when it scored particular successes should also be ones logicians should adopt. And, again, scientists have always adopted new logical methods in their pursuits. Dewey believed that logicians should do so too.
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