This is a long-awaited new edition of one of the best known Oxford Logic Guides. The book gives an introduction to intuitionistic mathematics, leading the reader gently through the fundamental mathematical and philosophical concepts. The treatment of various topics, for example Brouwer's proof of the Bar Theorem, valuation systems, and the completeness of intuitionistic first-order logic, have been completely revised.

The term verificationism is used in two different ways: the first is in relation to the verification principle of meaning, which we usually and rightly associate with the logical empiricists, although, as we now know, it derives in reality from Wittgenstein, and the second is in relation to the theory of meaning for intuitionistic logic that has been developed, beginning of course with Brouwer, Heyting and Kolmogorov in the twenties and early thirties, but in much more detail lately, particularly in (...) connection with intuitionistic type theory. It is therefore very natural to ask how these two forms of verificationism are related to one another: was the verificationism that we had in the thirties a kind of forerunner of what we have now, or was it something entirely different? I would like to discuss this question by considering a very particular problem, which was at the heart of Schlick’s interests, namely, the problem whether there might exist undecidable propositions or, if you prefer, unsolvable problems or unanswerable questions: it is merely a matter of wording which of these terms you choose. As I said, it is a problem which was at the heart of Schlick’s interests: it is explicitly discussed already in his early, programmatic paper Die Wende in der Philosophie in the first volume of Erkenntnis from 1930, and there is a short late paper, which has precisely Unanswerable Questions? as its title, from 1935, and he discussed it on several occasions in between also. (shrink)

Michael Dummett; VIII.—Truth, Proceedings of the Aristotelian Society, Volume 59, Issue 1, 1 June 1959, Pages 141–162, https://doi.org/10.1093/aristotelian/59.1.

Realism concerning a given subject-matter is characterised as a semantic doctrine with metaphysical consequences, namely as the adoption, for the relevant class of statements, of a truth-conditional theory of meaning resting upon the classical two-valued semantics. it is argued that any departure from classical semantics may, though will not necessarily, be seen as in conflict with some variety of realism. a sharp distinction is drawn between the rejection of realism and the acceptance of a reductionist thesis; though intimately related, neither (...) entails the other. realism is to be classified as "naive", "semi-naive" or "sophisticated": the first of these involves an all but unintelligible epistemological component. (shrink)

After the 1930s, the research into the foundations of mathematics changed.None of its main directions (logicism, formalism and intuitionism) had any longer the pretension to be the only true mathematics.Usually, the determining factor in the change is considered to be Gödel?s work, while Heyting?s role is neglected.In contrast, in this paper I first describe how Heyting directly suggested the abandonment of the big foundational questions and the putting forward of a new kind of foundational research consisting in the isolation of (...) formal, intuitive, logical and platonistic elements within classical mathematics.Furthermore, I describe how Heyting indirectly influenced the abandon?ment of the old directions of foundational research by making out some lists of degrees of evidence that exist within intuitionism. (shrink)

This book contains seminal discussions of central issues in the philosophy of language, mathematics, mind, religion and time. Is common language conceptually prior to idiolectics? What is a theory of meaning? Does constructivism provide a satisfactory account of mathematics? What are indefinitely extensible concepts? Can we change the past? These are only some of the very important questions addressed here. Both the papers written by the contributors and Dummett's replies provide a great wealth of stimulating ideas for those who currently (...) do research in the respective areas touched upon without making the reading exceedingly tedious. This feature, common to most of the papers in this book, makes it possible to use the material presented in undergraduate courses at university level. (shrink)

Radical conventionalism treats every necessary truth as a linguistic convention, akin to the statement ’There are seven days in a week’. Wittgenstein's endorsement of this view was a result of his belief that nothing can explain the fact of the acceptance of necessary truths. There could not be necessary truths being a consequence of human nature, which have not yet been recognized, or those which would never be recognized as such. This view stands in contrast to moderate conventionalism, which is (...) powerless to explain the necessity of logical consequence. (shrink)

Michael Dummett; VIII.—Truth, Proceedings of the Aristotelian Society, Volume 59, Issue 1, 1 June 1959, Pages 141–162, https://doi.org/10.1093/aristotelian/59.1.

Michael Dummett's three John Dewey Lectures--"The Concept of Truth," "Statements About the Past," and "The Metaphysics of Time"--were delivered at Columbia University in the spring of 2002. Revised and expanded, the lectures are presented here along with two new essays by Dummett, "Truth: Deniers and Defenders" and "The Indispensability of the Concept of Truth." In _Truth and the Past,_ Dummett clarifies his current positions on the metaphysical issue of realism and the philosophy of language. He is best known as a (...) proponent of antirealism, which loosely characterizes truth as what we are capable of knowing. The events of the past and statements about them are critical tests of an antirealist position. These essays continue and significantly contribute to Dummett's work. (shrink)

Realism has traditionally been understood as an epistemological doctrine about the direct awareness of the external objects. There is another sense of realism, in which one is said to be a realist about a particular subject matter. In the latter sense, it is a semantic thesis about the bivalence of the statements of the given subject matter. The anti‐realist semantical claim amounts to denying the possibility of knowing a statement to be true unless one has the means to arrive at (...) such knowledge. Dummett argues that only the semantic thesis is coherent, exploring interactions between the semantic versions of realism and anti‐realism. (shrink)