One of the most influential philosophers of the latter half of the twentieth century, Putnam (Professor of Mathematical Logic at Harvard University) has discussed epistemology only late in his career. But he has recently made some major contributions to this field: his arguments that truth is ultimately an epistemic concept, i.e., that truth and “ideal rational acceptability” (or ideal justification) are interdependent concepts and his criticisms of radical or evidence-transcendent scepticism. The two themes are tied together by Putnam’s defence of what he calls “internal realism”.
In the early 1970s Putnam was a staunch realist with respect to science and language. In both the philosophies of language and science, he argued for realism (see REALISM) against verificationism (see VERIFICATIONISM) (e.g. 1978, parts I and 3), and for the priority of reference over meaning (i.e. that most terms refer directly without mediating ideas, senses, or properties; cf e.g. Putnam, 1975). Against antirealism, Putnam argued truth couldn’t be warranted assertibility since we can recognize the possibility that a proposition might be warrantedly assertible but false (1978, part 3). However, about 1976, Putnam’s philosophy took a dramatic turn. He abandoned his view that truth was essentially non-epistemic and instead argued that truth was idealized warranted assertibility (1978, part 4; 1981).
A key step in his development was Putnam’s realization that, on his own view, evidence-transcendent scepticism was self-refuting. One naïvely assumes that if we were all brains in a vat (assuming we’re not now), then the sentence “we are brains in a vat” would continue to mean just what it does now and so would be true in the vat case. But this is to assume meanings “are in the head,” an assumption repudiated by Putnam’s causal or direct theory of reference. In fact, in a world in which we were all brains in a vat, there would be a “referential shift” and the sentence “we are brains in a vat” would mean something very different. While “brains” now refers directly to certain organs, in the vat world “brains” would refer directly to aspects of the computer program, perhaps, controlling the subjects’ brain-images; similarly for “vats”. But then in that case, the brains’ assertion “we are brains in a vat” would be false, since they are not aspects of a computer program. Consequently, the utterance “we are brains in a vat” is always false, regardless of who says it and so radical scepticism is refuted (Putnam, 1981). It is useful to compare Putnam’s analysis to Skolem’s paradox where, because of a similar referential shift, the sentence “the real numbers are uncountable” is true not only for us in an uncountable world but even true in a countable model of set theory! (Tymoczko, 1990).
The residual feeling that we could somehow step outside the world (or model) and discover that we really were brains in a vat is an expression of what Putnam calls “metaphysical realism” (Putnam, 1978, part 4; 1981). He points out that this view is, strictly speaking, false or incoherent. It is false if expressed in our language (since “we are brains in a vat” is false). Moreover, to the response “Yes, but if we could adopt a God’s eye point of view we’d see we really are brains in a vat”. Putnam could reply that this requires using a language other than the language we now use – in order to say “we really are brains in a vat” and make it come out true. In that case, the quoted sentence is meaningless. (In analogous fashion, the sentence “the reals are countable” is either trivially false by Cantor’s Theorem, or else a sentence of a language that by hypothesis, we don’t understand.)
For Putnam, “metaphysical realism” is the view that even an epistemically ideal theory could be false (in other words, that truth is non-epistemic). His recent argument purports to show this view has no content. Nevertheless, if we abandon metaphysical realism, we should still hold to the internal or pragmatic realism suggested by Peirce (see PEIRCE), according to Putnam. Internal realism is realism about science and language, but only as an empirical theory internal to science. It is stronger than verificationism (because true beliefs are not justified beliefs but only ideally justified beliefs) and it still maintains the priority of reference over meaning, and in this sense is realist. On the other hand, reference is seen as dependent on use and on what can be ideally verified, and since truth is tied to reference, truth too is an epistemic concept. Crudely: the only criterion for what is a fact is what it is (ideally) rational to accept (and so bivalence might not be preserved since, for certain p, it might not be ideally rational either to accept p or to reject it). Thus, truth and justification are two separate, but interdependent notions. (Putnam 1981, 1989).
(Putnam’s argument can be formulated more abstractly in model theoretic terms, as in Putnam, 1983, 1981. For a concise summary of internal realism, see Putnam, 1989.)
See also ANALYTICITY; PRAGMATISM; REALISM; SCEPTICISM, CONTEMPORARY; TRUTH.
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