MATHEMATICAL EPISTEMOLOGY AND PSYCHOLOGY SYNTHESE LIBRARY MONOGRAPHS ON EPISTEMOLOGY, LOGIC, METHODOLOGY, PHILOSOPHY OF SCIENCE, SOCIOLOGY OF SCIENCE AND OF KNOWLEDGE, AND ON THE MATHEMATICAL METHODS OF SOCIAL AND BEHA VIORAL SCIENCES Editors: DONALD DAVIDSON, Stanford University J AAKKO HINTIKKA, University of Helsinki and Stanford University GABRIEL NUCHELMANS, University of Leyden WESLEY C. SALMON, Indiana University EVERT W. BETH / JEAN PIAGET MATHEMATICAL EPISTEMOLOGY AND PSYCHOLOGY Translated from the French by W. Mays SPRINGER-SCIENCE+BUSINESS MEDIA, B.V. EPISTEMOLOGIE MATHEMATIQUE ET PSYCHOLOGIE First published by Presses Universitaires de France, Paris as Volume XIV of the' Etudes d' Epistem%gie Genbique' ISBN 978-90-481-8328-9 ISBN 978-94-017-2193-6 (eBook) DOI 10.1007/978-94-017-2193-6 All rights reserved No part of this book may be reproduced in any form, by print, photoprint, microfilm, or any other means without permission from the publisher Softcover reprint of the hardcover 1st edition 1966 TABLE OF CONTENTS IN MEMORY OF E. W. BETH (1908-1964) XI TRANSLATOR'S INTRODUCTION XIII FOREWORD XXI EVERTW. BETH/PART ONE PRELIMINARY 3 CHAPTER I. MATHEMATICAL REASONING CANNOT BE ANALYSED BY TRADITIONAL SYLLOGISTICS 6 1. Descartes 6 2. The Locke-Berkeley problem 7 3. Solutions of Berkeley, Hume and Kant 8 4. Analytic and synthetic judgments 12 5. The intuitionism of Descartes and Kant 14 6. Non-Euclidean geometry 17 7. Recent forms of intuitionism: F. A. Lange, L. Brunschvicg, E. Goblot, H. Poincare, L. E. J. Brouwer 18 CHAPTER II. THE PSYCHOLOGICAL INTERPRETATION OF MA THEMA TICAL REASONING 24 8. J. Stuart Mill 24 9. W. Stanley Jevons' critique 25 10. E. Mach, Th. Ziehen, G. Storring and G. Heymans 26 11. The supposed anti-psychologism of E. HusserI 30 12. F. Enriques and G. Mannoury 33 v MATHEMATICAL EPISTEMOLOGY AND PSYCHOLOGY CHAPTER III. THE LOGICIST TRADITION 13. Aristotle's views: agreement with the practice of Greek mathematics 36 14. Pascal 38 15. Leibniz: demonstration of axioms 39 16. Frege: influence on HusserI and Heymans 41 17. Russell: the crisis of foundations 42 18. The Set Theorists: Cantor and Zermelo 44 19. Other reactions: the intuitionism of Brouwer, the psycho1ogism of Mannoury and Enriques, the radical formalism of Hilbert 46 20. The GOde1ian crisis 53 21. Natural deduction: Gentzen, Curry, Lorenzen 59 22. Syntax and semantics 68 23. The method of semantic tableaux 71 24. Algebraic and topological concepts 81 CHAPTER IV. STRICT DEMONSTRATION AND HEURISTIC PROCEDURES 86 25. The typology of mathematicians 86 26. Views of Poincare, Hadamard, Po1ya 87 27. Search for a method which is both heuristic and demonstrative: Descartes and the analysis of the Ancients 93 28. Leibniz and the decision problem 95 29. Persistence of more primitive levels: Archimedes' method 96 30. Original thought: creation or invention, construction or discovery? The Platonist reply: Frege, Cantor and Hermite 98 CHAPTER V. INTUITIVE STRUCTURES AND FORMALISED MATHEMATICS 101 31. Spatial intuition: Kant, Helmholtz, F. Klein, Nicod, Whitehead and Tarski 101 32. Temporal intuition: Kant, Bergson, Brouwer and De Groot 105 VI T ABLE OF CONTENTS 33. Finitist intuition according to Hilbert and the intuition of the infinite 108 34. Platonism as a real or illusory intuitive vision: the nominalist critique 111 CHAPTER VI. "THINKING MACHINES" AND MATHEMATICAL THOUGHT 114 35. Formalisation and the construction of a "thinking machine" 114 36. The construction of a "thinking machine" presupposes the solution of a decision problem 115 37. The irreducibility of the "leap from the end to the means" according to Brouwer 118 38. Recursive functions: unsolvable problems, absolute unsolvability 119 39. The two degrees of freedom of mathematical thought: solving a problem and setting a problem 123 40. Acquired self-evidence according to Bernays 124 NOTE ON THE IDEA OF A "THINKING MACHINE" by Jean-Blaise Grize 127 JEAN PIAGET/PART TWO PRELIMINARY 131 CHAPTER VII. LESSONS OF THE HISTORY OF THE RELATIONS BETWEEN LOGIC AND PSYCHOLOGY 137 41. The three stages of the history of the relations between logical and psychological investigations 137 42. The need for co-ordination 143 43. The genetic viewpoint and the normative viewpoint 153 CHAPTER VIII. GENERAL PSYCHOLOGICAL PROBLEMS OF LOGICO-MATHEMATICAL THOUGHT 163 A. The problem of structures 163 44. Bourbaki's "matrix structures" 164 VII MATHEMATICAL EPISTEMOLOGY AND PSYCHOLOGY 45. The structures of classes and relations in the subject's actions and operations. The formalisation of a "grouping" 166 46. The two forms of reversibility (inversion and reciprocity) and their final combination in a group of four transformations 175 47. The primacy of topology in the child's geometry 183 48. Relations between the three elementary structures and Bourbaki's matrix structures 186 CHAPTER IX. GENERAL PSYCHOLOGICAL PROBLEMS OF LOGICO-MATHEMATICAL THOUGHT (Continued) 191 B. Self-evidence, intuition and invention 191 49. Self-evidence, its variations and logical necessity 191 50. Invention and discovery 198 51. The multiple forms of mathematical "intuition" 208 CHAPTER X. THE PSYCHOLOGICAL PROBLEMS OF "PURE" THOUGHT 226 52. The genetic roots of pure mathematics 226 53. The psychological problem of pure mathematics 242 54. The psychological reasons for formalisation 247 55. How a formalisation of ordinary thought brings together the genetic and axiomatic methods 256 CHAPTER XI. SOME CONVERGENCES BETWEEN FORMAL AND GENETIC ANALYSES 259 56. The construction of natural numbers 259 57. The difficulties of logical reductionism 272 58. The limits of formalisation 276 CHAPTER XII. EPISTEMOLOGICAL PROBLEMS WITH LOGICAL AND PSYCHOLOGICAL RELEVANCE 281 59. Empiricist interpretation and apriorism 281 VIII TABLE OF CONTENTS 60. The nominalist or linguistic interpretation of mathematics 285 61. The Platonist interpretation of mathematics 290 62. The interpretation of mathematics by the laws of the general co-ordination of actions 296 GENERAL CONCLUSIONS 305 by Evert W. Beth and Jean Piaget BIBLIOGRAPHY 313 NAME INDEX 318 SUBJECT INDEX 321 IX IN MEMORY OF E. W. BETH (1908-1964) It is with great regret that I begin this volume by recalling to the reader the premature death of E. W. Beth. He had taken great pleasure in this English translation, the excellent work of W. Mays, and had looked through the text with his usual thoroughness. E. W. Beth was a great logician, who was also extremely well acquainted with all aspects of the history of logic and its connections with other disciplines, and this essentially determined his epistemological position. At the beginning of the first part of this book he relates how, starting from a position close to Kantianism and from reflections on Mannoury's psycho-linguistics and the psychological factors involved in Brouwer's intuitionism, he arrived - by a kind of "intellectual conversion" - at an attitude more exclusively formalist and logicist. When I made his acquaintance around 1950 he was, in fact, mistrustful of everything connected with, or even in any way evocative of, psychology. It is thus well worth remembering the origin of the present work, for it is to the credit of Beth and of his final position, which was charac terised, as he says in his introduction, by "the constant effort to see every point of view as a reasonable one" and by an appreciation of "the need for a kind of doctrinal synthesis of the various trends of contemporary thought". In 1950 I published a work on the operational mechanisms of logic, which my publisher decided to call Traite de Logique: Beth criticised it very severely in the journal Methodos. Father Bochenski, who had requested this review, refused to publish my reply, which I then reduced to a few lines, saying, in effect, that if two authors fail to understand each other because their points of view are so divergent, the only way of achieving some useful and objective result is for them to co-operate in the preparation of a joint work, where the same data are investigated one by one until a mutually satisfactory assimilation of their positions is reached. It was along such lines that I wrote to Beth and invited him to participate in various meetings, where we discussed the psychological formation and development of certain elementary logical structures. It is a measure of XI
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