# Defending the Axioms: On the Philosophical Foundations of Set Theory

## Penelope Maddy

### Abstract

Mathematics depends on proofs, and proofs have to begin somewhere, from some fundamental assumptions. Chapter I traces the historical rise of pure mathematics and the development of set theory, eventually axiomatic set theory, to play this foundational role for contemporary classical mathematics. Here the Euclidean ideal of postulates that are simply obvious or self-evident can't be the whole story, which raises two basic questions: what are the proper methods for defending set-theoretic axioms? And, why are these the proper methods? Chapter II introduces the meta-philosophical perspective, ca ... More

Mathematics depends on proofs, and proofs have to begin somewhere, from some fundamental assumptions. Chapter I traces the historical rise of pure mathematics and the development of set theory, eventually axiomatic set theory, to play this foundational role for contemporary classical mathematics. Here the Euclidean ideal of postulates that are simply obvious or self-evident can't be the whole story, which raises two basic questions: what are the proper methods for defending set-theoretic axioms? And, why are these the proper methods? Chapter II introduces the meta-philosophical perspective, called Second Philosophy, from which the inquiry into these questions will take place, and identifies straightforward mathematical answers to the first question. Addressing the second requires engagement with the troublesome ontological and epistemological issues that have dogged the philosophy of mathematics from its beginnings. Chapters III and IV describe and explore two apparently conflicting stands on these issues—called Thin Realism and Arealism—not so much to recommend either one, but with an eye to suggesting that the question of which is correct has less bite than it might appear. In the end, the hope is to shift attention away from these elusive matters of truth and existence, and to direct it toward the distinctive type of mathematical objectivity emphasized in the opening section of Chapter V. The concluding sections of chapter V return, at last, to the question of set-theoretic method and draw some concrete morals for the project of defending the axioms.

*Keywords: *
axioms,
epistemology,
mathematical existence,
mathematics,
set-theoretic methods,
objectivity,
ontology,
Second Philosophy,
set theory,
mathematical truth

### Bibliographic Information

Print publication date: 2011 |
Print ISBN-13: 9780199596188 |

Published to Oxford Scholarship Online: May 2011 |
DOI:10.1093/acprof:oso/9780199596188.001.0001 |