
467Brouwerian intuitionismMind 99 (396): 501534. 1990.The aims of this paper are twofold: firstly, to say something about that philosophy of mathematics known as 'intuitionism' and, secondly, to fit these remarks into a more general message for the philosophy of mathematics as a whole. What I have to say on the first score can, without too much inaccuracy, be compressed into two theses. The first is that the intuitionistic critique of classical mathematics can be seen as based primarily on epistemological rather than on meaningtheoretic considerat…Read more

220Purity of MethodsPhilosophers' Imprint 11. 2011.Throughout history, mathematicians have expressed preference for solutions to problems that avoid introducing concepts that are in one sense or another “foreign” or “alien” to the problem under investigation. This preference for “purity” (which German writers commonly referred to as “methoden Reinheit”) has taken various forms. It has also been persistent. This notwithstanding, it has not been analyzed at even a basic philosophical level. In this paper we give a basic analysis of one conception …Read more

211The fourcolor theorem and mathematical proofJournal of Philosophy 77 (12): 803820. 1980.I criticize a recent paper by Thomas Tymoczko in which he attributes fundamental philosophical significance and novelty to the latelypublished computerassisted proof of the four color theorem (4CT). Using reasoning precisely analogous to that employed by Tymoczko, I argue that much of traditional mathematical proof must be seen as resting on what Tymoczko must take as being "empirical" evidence. The new proof of the 4CT, with its use of what Tymoczko calls "empirical" evidence is therefore not…Read more

194On an alleged refutation of Hilbert's program using gödel's first incompleteness theoremJournal of Philosophical Logic 19 (4). 1990.It is argued that an instrumentalist notion of proof such as that represented in Hilbert's viewpoint is not obligated to satisfy the conservation condition that is generally regarded as a constraint on Hilbert's Program. A more reasonable soundness condition is then considered and shown not to be counterexemplified by Godel's First Theorem. Finally, attention is given to the question of what a theory is; whether it should be seen as a "list" or corpus of beliefs, or as a method for selecting be…Read more

188What does Gödel's second theorem say?Philosophia Mathematica 9 (1): 3771. 2001.We consider a seemingly popular justification (we call it the Reflexivity Defense) for the third derivability condition of the HilbertBernaysLöb generalization of Godel's Second Incompleteness Theorem (G2). We argue that (i) in certain settings (rouglily, those where the representing theory of an arithmetization is allowed to be a proper subtheory of the represented theory), use of the Reflexivity Defense to justify the tliird condition induces a fourth condition, and that (ii) the justificat…Read more

174Poincaré against the logiciansSynthese 90 (3). 1992.Poincaré was a persistent critic of logicism. Unlike most critics of logicism, however, he did not focus his attention on the basic laws of the logicists or the question of their genuinely logical status. Instead, he directed his remarks against the place accorded to logical inference in the logicist's conception of mathematical proof. Following Leibniz, traditional logicist dogma (and this is explicit in Frege) has held that reasoning or inference is everywhere the same — that there are no prin…Read more

141On interpreting Gödel's second theoremJournal of Philosophical Logic 8 (1). 1979.In this paper I have considered various attempts to attribute significance to Gödel's second incompleteness theorem (G2 for short). Two of these attempts (BethCohen and the position maintaining that G2 shows the failure of Hilbert's Program), I have argued, are false. Two others (an argument suggested by Beth, Cohen and ??? and Resnik's Interpretation), I argue, are groundless.

106Proof: Its nature and significanceIn Bonnie Gold & Roger A. Simons (eds.), Proof and Other Dilemmas: Mathematics and Philosophy, Mathematical Association of America. pp. 1. 2008.I focus on three preoccupations of recent writings on proof. I. The role and possible effects of empirical reasoning in mathematics. Do recent developments (specifically, the computerassisted proof of the 4CT) point to something essentially new as regards the need for and/or effects of using broadly empirical and inductive reasoning in mathematics? In particular, should we see such things as the computerassisted proof of the 4CT as pointing to the existence of mathematical truths of which we c…Read more

103An Essay on Mathematical Instrumentalism M. Detlefsen. THE PHILOSOPHICAL FUNDAMENTALS OF HILBERT'S PROGRAM 1. INTRODUCTION In this chapter I shall attempt to set out Hilbert's Program in a way that is more revealing than ...

89Poincaré vs. Russell on the rôle of logic in mathematicstPhilosophia Mathematica 1 (1): 2449. 1993.In the early years of this century, Poincaré and Russell engaged in a debate concerning the nature of mathematical reasoning. Siding with Kant, Poincaré argued that mathematical reasoning is characteristically nonlogical in character. Russell urged the contrary view, maintaining that (i) the plausibility originally enjoyed by Kant's view was due primarily to the underdeveloped state of logic in his (i.e., Kant's) time, and that (ii) with the aid of recent developments in logic, it is possible t…Read more

89Wright on the nonmechanizability of intuitionist reasoningPhilosophia Mathematica 3 (1): 103119. 1995.Crispin Wright joins the ranks of those who have sought to refute mechanist theories of mind by invoking Gödel's Incompleteness Theorems. His predecessors include Gödel himself, J. R. Lucas and, most recently, Roger Penrose. The aim of this essay is to show that, like his predecessors, Wright, too, fails to make his case, and that, indeed, he fails to do so even when judged by standards of success which he himself lays down.

89Löb's theorem as a limitation on mechanismMinds and Machines 12 (3): 353381. 2002.We argue that Löb's Theorem implies a limitation on mechanism. Specifically, we argue, via an application of a generalized version of Löb's Theorem, that any particular device known by an observer to be mechanical cannot be used as an epistemic authority (of a particular type) by that observer: either the beliefset of such an authority is not mechanizable or, if it is, there is no identifiable formal system of which the observer can know (or truly believe) it to be the theoremset. This gives, …Read more

83Fregean hierarchies and mathematical explanationInternational Studies in the Philosophy of Science 3 (1). 1988.There is a long line of thinkers in the philosophy of mathematics who have sought to base an account of proof on what might be called a 'metaphysical ordering' of the truths of mathematics. Use the term 'metaphysical' to describe these orderings is intended to call attention to the fact that they are regarded as objective and not subjective and that they are conceived primarily as orderings of truths and only secondarily as orderings of beliefs. / I describe and consider two models for such or…Read more

80FormalismIn Stewart Shapiro (ed.), Oxford Handbook of Philosophy of Mathematics and Logic, Oxford University Press. pp. 236317. 2005.A comprehensive historical overview of formalist ideas in the philosophy of mathematics.

76Walter van Stigt. Brouwer's Intuitionism. Amsterdam: NorthHolland Publishing Co., 1990. pp. xxvi + 530. ISBN 0444883843 (Cloth) (review)Philosophia Mathematica 6 (2): 235241. 1998.

70Proof and Knowledge in Mathematics (edited book)Routledge. 1992.These questions arise from any attempt to discover an epistemology for mathematics. This collection of essays considers various questions concerning the nature of justification in mathematics and possible sources of that justification. Among these are the question of whether mathematical justification is _a priori_ or _a posteriori_ in character, whether logical and mathematical differ, and if formalization plays a significant role in mathematical justification

67Constructive existence claimsIn Matthias Schirn (ed.), The Philosophy of Mathematics Today: Papers From a Conference Held in Munich From June 28 to July 4,1993, Clarendon Press. pp. 1998307. 1998.It is a commonplace of constructivist thought that a claim that an object of a certain kind exists is to be backed by an explicit display or exhibition of an object that is manifestly of that kind. Let us refer to this requirement as the exhibition condition. The main objective of this essay is to examine this requirement and to arrive at a better understanding of its epistemic character and the role that it plays in the two main constructivist philosophies of this centurythe intuitionist pro…Read more

66Ian Hacking. Why Is There Philosophy of Mathematics At All?Philosophia Mathematica 25 (3): 407412. 2017.© The Author [2017]. Published by Oxford University Press. All rights reserved. For permissions, please email: [email protected] author makes clear that he does not see this book as a contribution to the philosophy of mathematics as traditionally understood. He takes it instead to be an essay about the philosophy of mathematics, one whose purpose is to explain its existence and to make clear the limited extent to which its current and past forms are properly regarded as philosophi…Read more

58On a theorem of FefermanPhilosophical Studies 38 (2). 1980.In this paper I argue that Feferman's theorem does not signify the existence of skepticsatisfying consistency proofs. However, my argument for this is much different than other arguments (most particularly Resnik's) for the same claim. The argument that I give arises form an analysis of the notion of 'expression', according to which the specific character of that notion is seen as varying from one context of application (of a result of arithmetic metamathematics) to another.

55Mind in the shadowsStudies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 29 (1): 123136. 1998.This is a review of Penrose's trilogy, The Emperor's New Mind, Shadows of the Mind and The Large the Small and the Human Mind.

53The mechanization of reasonPhilosophia Mathematica 3 (1). 1995.Introduction to a special issue of Philosophia Mathematica on the mechanization of reasoning. Authors include: M. Detlefsen, D. Mundici, S. Shanker, S. Shapiro, W. Sieg and C. Wright.

4620002001 Spring Meeting of the Association for Symbolic LogicBulletin of Symbolic Logic 7 (3): 413419. 2001.

45Poincaré versus Russell sur le rôle de la logique dans les mathématiquesLes Etudes Philosophiques 97 (2): 153. 2011.Au début du XXe siècle, Poincaré et Russell eurent un débat à propos de la nature du raisonnement mathématique. Poincaré, comme Kant, défendait l’idée que le raisonnement mathématique était de caractère non logique. Russell soutenait une conception contraire et critiquait Poincaré. Je défends ici l’idée que les critiques de Russell n’étaient pas fondées.In the early twentieth century, Poincare and Russell engaged in a discussion concerning the nature of mathematical reasoning. Poincare, like Kan…Read more

31Essay ReviewHistory and Philosophy of Logic 9 (1): 93105. 1988.S. SHAPIRO (ed.), Intensional Mathematics (Studies in Logic and the Foundations of Mathematics, vol. 11 3). Amsterdam: NorthHolland, 1985. v + 230 pp. $38.50/100Df

30Proof, Logic and Formalization (edited book)Routledge. 1992.The mathematical proof is the most important form of justification in mathematics. It is not, however, the only kind of justification for mathematical propositions. The existence of other forms, some of very significant strength, places a question mark over the prominence given to proof within mathematics. This collection of essays, by leading figures working within the philosophy of mathematics, is a response to the challenge of understanding the nature and role of the proof.

26Formalism and Hilbert’s understanding of consistency problemsArchive for Mathematical Logic 60 (5): 529546. 2021.Formalism in the philosophy of mathematics has taken a variety of forms and has been advocated for widely divergent reasons. In Sects. 1 and 2, I briefly introduce the major formalist doctrines of the late nineteenth and early twentieth centuries. These are what I call empiricosemantic formalism, game formalism and instrumental formalism. After describing these views, I note some basic points of similarity and difference between them. In the remainder of the paper, I turn my attention to Hilber…Read more

23Introduction to Logicism and the Paradoxes: A ReappraisalNotre Dame Journal of Formal Logic 41 (3): 185185. 2000.

22Duality, Epistemic Efficiency and ConsistencyIn G. Link (ed.), Formalism & Beyond, . pp. 124. 2014.Duality has often been described as a means of extending our knowledge with a minimal additional outlay of investigative resources. I consider possible arguments for this view. Major elements of this argument are out of keeping with certain widely held views concerning the nature of axiomatic theories (both in projective geometry and elsewhere). They also require a special form of consistency requirement.
Michael Detlefsen
(1948  2019)
Notre Dame, Indiana, United States of America
Areas of Specialization
Logic and Philosophy of Logic 
Philosophy of Mathematics 