The Logical Basis of Metaphysics by Michael Dummett (review)

356 BOOK REVIEWS The Logical Basis of Metaphysics. By MICHAEL DUMMETT; The William James Lectures, 1976. Cambridge, Mass.: Harvard University Press, 1991. Pp. xi + 355. $34.95 (cloth). Michael Dummett, who is Wykeham Professor of Logic at Oxford, represents an influential force in contemporary analytical philosophy . In the tradition of Gottlob Frege and Ludwig Wittgenstein, Dum· mett has contributed significant works in philosophy of language (theory of meaning) and intuitionistic logic as well as in current metaphysics , liberated from the neopositivistic imprisonment. Dummett's newest book has a self-explanatory title and is based on the William James Lectures which he delivered at Harvard University in 1976. As he explains in his Preface (1989), the publication of these lectures, however delayed and edited, should show the importance of the theory of meaning " for its more glamorous relative, metaphysics." Dummett is known as the leading proponent of "anti-realism "-a position endorsed , for instance, by Hilary Putnam-and the book under review amply demonstrates his views on this current controversial issue. Various " anti-realists," Dummett contends, share their rejection of the prin· ciple of bivalence (according to which every proposition is determinately either true or false) and of the related law of the excluded middle. Such rejections require the acceptance of " stricter canons of valid deductive reasoning" (p. 11), which, in turn, demand tightened and clarified concepts of meaning and truth or, in Wittgenstein's phrase, "a clear view of the working of our language." (p. 13). What one needs, in short, is a good theory of meaning which will " determine the correct logic " of a language and also settle various metaphysical controversies with regard to the nature of physical reality, time, mind, mathematics , etc. Dummett understands such theory of meaning as the key part of the philosophy of thought that has been so much stimulated by Frege's theory of sense and reference. Dummett's methodology de· mands therefore the following order: a good theory of meaning leading to " correct " logic, which in turn helps to settle metaphysical controversies . He aspires to show " how the choice between different logics arises at the level of the theory of meaning" (p. 18) and makes no apologies for using in this process a highly technical conceptual apparatus of mathematical logic. By his own admission, Dummett does not want to raise classical metaphysical questions of God, free will, and immortality, but "others almost equally profound" yet requiring a "painfully slow pace of advance" (p. 19). In spite of such declarations Dummett touches upon the problem of BOOK REVIEWS 357 God's omniscience: if, determinately, one of two possibilities holds, then God must know which of the two possibilities it is. Yet this example is utilized by Dummett not because of its theological impact (which he seems to take for granted) hut for the service it can provide in clarifying the problem of hivalence. At the very end of the last chapter, entitled ".Realism and the Theory of Meaning," Dummett concludes that the premise which expresses God's omniscience does not entail that God knows whether any given proposition is true or false nor does such a premise entail that the proposition is either true or false. Allegedly , an additional premise is needed asserting the truth or the falsehood of the proposition in question (whichever the case) " in order to deduce from his omniscience that he knows, in the sense stated, whether it is true or false" (p. 351). This anti-realistic position is thus based on the rejection of classical, two-valued logic and on the endorsement of intuitionistic logic, developed by the Dutch mathematician Brouwer and his followers, including Dummett himself (see his Elements of Intuitwnism, published in 1977 by Oxford Clarendon Press) . According to this logic, if a statement is true only if we are able to prove it (to provide or construct evidence for it, etc.) , then " there is no ground to assume every statement to he either true or false" (p. 9). Dummett claims that intuitionistic logic is supported by a verificationist meaningtheory which gets a large share of his attention. In the verificationist theory of meaning, " the meaning of a statement is determined by what we acknowledge as grounds...