Poincaré's Philosophy of Mathematics and the Impossibility
Total Page:16
File Type:pdf, Size:1020Kb
POINCARÉ’S PHILOSOPHY OF MATHEMATICS AND THE IMPOSSIBILITY OF BUILDING A NEW ARITHMETIC A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF SOCIAL SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY BY KORAY AKÇAGÜNER IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS IN THE DEPARTMENT OF PHILOSOPHY SEPTEMBER 2019 Approval of the Graduate School of Social Sciences Prof. Dr. Yaşar Kondakçı Director I certify that this thesis satisfies all the requirements as a thesis for the degree of Master of Arts. Prof. Dr. Ş. Halil Turan Head of Department This is to certify that we have read this thesis and that in our opinion it is fully adequate, in scope and quality, as a thesis for the degree of Master of Arts. Assoc. Prof. M. Hilmi Demir Supervisor Examining Committee Members Prof. Dr. David Grunberg (METU, PHIL) Assoc. Prof. M. Hilmi Demir (METU, PHIL) Prof. Dr. H. Bülent Gözkan (MSGSU, Felsefe) I hereby declare that all information in this document has been obtained and presented in accordance with academic rules and ethical conduct. I also declare that, as required by these rules and conduct, I have fully cited and referenced all material and results that are not original to this work. Name, Last name: Koray Akçagüner Signature : iii ABSTRACT POINCARÉ’S PHILOSOPHY OF MATHEMATICS AND THE IMPOSSIBILTY OF BUILDING A NEW ARITHMETIC AKÇAGÜNER, Koray M.A., Department of Philosophy Supervisor: Assoc. Prof. M. Hilmi Demir September 2019, 100 pages This thesis examines Poincaré’s philosophy of mathematics, in particular, his rejection of the possibility of building a new arithmetic. The invention of non- Euclidean geometries forced Kant’s philosophy of mathematics to change, leading thinkers to doubt the idea that Euclidean postulates are synthetic a priori judgments. Logicism and formalism have risen during this period, and these schools aimed to ground mathematics on a basis other than the one that was laid down by Kant. With regards to the foundations of mathematics, Poincaré adopted Kant’s philosophy and remained an intuitionist, though naturally, he had to make significant changes in Kant’s thought. Poincaré argued that the branch of mathematics that contains synthetic a priori judgments is arithmetic, which is completely independent of experience and therefore pure. What gives arithmetic its object of knowledge and justifies the use of its fundamental principles is not experience, but a pure intuition. On the other hand, Poincaré claimed that our ideas about space and the geometric postulates are not imposed upon us, that they are not known a priori but are rather conventions – “definitions in disguise”. The role experience plays in the foundations of geometry has given us the possibility of building non-Euclidean geometries. However, since arithmetic is completely independent of experience, it is not possible iv for a change similar to that in geometry to take place in arithmetic, which would alter its basic concepts or principles that we consider to be true. It is argued in this thesis that it is possible to develop the intuition which lies at the basis of arithmetic and this may become the starting point of a new arithmetic. It will be shown that this is what Cantor has actually achieved when establishing transfinite ordinal arithmetic. Keywords: Intuitionism, conventionalism, synthetic a priori, non-Euclidean geometries, transfinite arithmetic. v ÖZ POINCARÉ’NİN MATEMATİK FELSEFESİ VE YENİ BİR ARİTMETİK İNŞA ETMENİN OLANAKSIZLIĞI AKÇAGÜNER, Koray Yüksek Lisans, Felsefe Bölümü Tez Yöneticisi: Doç. Dr. M. Hilmi Demir Eylül 2019, 100 sayfa Bu tez Poincaré’nin matematik felsefesini, özel olarak da kendisinin yeni bir aritmetik kurmanın imkanını reddedişini incelemektedir. Öklid-dışı geometrilerin icadı Kant’ın matematik felsefesini değişime zorlamış, düşünürleri Öklid postulatlarının sentetik a priori yargılar olduğu fikrinden şüphe duymaya itmiştir. Mantıkçılık ve biçimcilik okulları bu dönemde yükselmiş ve matematiği Kant’ın öne sürdüğü temellerden başka temellere oturtmayı amaçlamıştır. Poincaré ise matematiğin temellerine dair Kant’ın felsefesini benimsemiş ve sezgici kalmıştır; fakat elbette Kant’ın düşüncesinde köklü değişiklikler yapması gerekmiştir. Poincaré matematiğin sentetik a priori yargılar barındıran alanının, deneyimden tümüyle bağımsız ve dolayısıyla saf olan aritmetik olduğunu öne sürmüştür. Aritmetiğe bilgi nesnesini veren ve temel ilkelerinin kullanımını meşru kılan şey deneyim değil, saf bir sezgidir. Buna karşın Poincaré, uzaya dair fikirlerimizin ve geometrik postulatların ise bize dayatılmadığını, bunların a priori bilinmediğini ve aslında birtakım uzlaşımlar, “kılık değiştirmiş tanımlar” olduğunu söylemiştir. Deneyimin geometrinin temellerindeki payı bize Öklid-dışı geometriler kurmanın imkanını vermiştir; fakat aritmetik tümüyle deneyimden bağımsız olduğundan, geometridekine benzer bir değişimin aritmetikte yaşanması ve buradaki temel kavramların veya doğru kabul edilen ilkelerin değişmesi mümkün değildir. Bu tez, aritmetiğin vi temelinde yatan sezginin geliştirilebileceğini ve bunun da yeni bir aritmetiğin başlangıç noktası olabileceğini öne sürmektedir. Cantor’un sonluötesi ordinal aritmetiği kurarken esasında bunu başardığı gösterilecektir. Anahtar Kelimeler: Sezgicilik, uzlaşımcılık, sentetik a priori, Öklid-dışı geometriler, sonluötesi aritmetik. vii To My Parents viii ACKNOWLEDGMENTS The author wishes to express his deepest gratitude to his supervisor Assoc. Prof. Mehmet Hilmi Demir for his patience, friendship, guidance, and criticism throughout the work. The author would also like to thank Mr. Çöteli and Mr. Şahin for their assistance, and to Ms. Akgül for her kind support. ix TABLE OF CONTENTS PLAGIARISM ................................................................................................................. iii ABSTRACT ..................................................................................................................... iv ÖZ .................................................................................................................................. vi DEDICATION ............................................................................................................... viii ACKNOWLEDGMENTS ................................................................................................ ix TABLE OF CONTENTS ................................................................................................... x LIST OF FIGURES ......................................................................................................... xii CHAPTER 1. INTRODUCTION ...................................................................................................... 1 2. KANT’S PHILOSOPHY OF MATHEMATICS ....................................................... 4 2.1. The Distinction Between Analytic and Synthetic Judgments ...................... 5 2.2. Mathematical Propositions are Synthetic Judgments .................................. 9 2.3. The Truth of Mathematical Propositions is Known A Priori ..................... 10 2.4. Forms of Sensibility: Space and Time ........................................................ 11 2.4.1 Arithmetic and Time ........................................................................... 13 2.4.2 Geometry and Space ........................................................................... 14 2.5. Summary ..................................................................................................... 15 3. POINCARÉ’S PHILOSOPHY OF MATHEMATICS ............................................ 18 3.1. The Intellectual Climate after Kant ............................................................ 18 3.2. Poincaré Against Logicism and Formalism ................................................ 21 3.3. Poincaré’s Intuitionism ............................................................................... 25 3.4. Mathematical Induction and the Intuition of Pure Number ........................ 29 3.4.1. The Intuition of Pure Number and Time ........................................... 34 3.4.2. The Difference in the Foundations of Arithmetic and Geometry ...... 36 3.5. Conventionalism in Geometry .................................................................... 38 3.5.1. Conditions for Constituting Geometry .............................................. 41 3.5.1.1. A priori Conditions ................................................................. 41 x 3.5.1.2. Empirical Conditions .............................................................. 46 3.6. Summary .................................................................................................... 50 4. CANTOR’S TRANSFINITE ORDINAL ARITHMETIC ...................................... 53 4.1. Theory of the Actual Mathematical Infinite ............................................... 56 4.1.1. Cantor’s Response to Aristotle’s Rejection of Actual Infinity .......... 58 4.1.2. The Intuition of Pure Number and Potential Infinity ........................ 61 4.2. Fundementals of Transfinite Ordinal Arithmetic ....................................... 62 4.2.1. Formal Notation................................................................................. 68 4.3. Objections to Transfinite Ordinal Arithmetic ............................................ 74 5. CONCLUSION ........................................................................................................ 82 REFERENCES ........................................................................................................