Relative Categoricity and Abstraction Principles

TL;DR

This paper examines the relative categoricity of abstraction principles in the philosophy of mathematics, showing that most are not naturally relatively categorical, highlighting a tension between foundational axiomatizations and abstraction-based approaches.

Contribution

It demonstrates that most abstraction principles lack natural relative categoricity, contrasting with the categoricity of Hume's Principle, and compares these criteria with other logical and stability conditions.

Findings

Hume's Principle is naturally relatively categorical.

Most other abstraction principles are not relatively categorical.

There is a significant tension between categoricity and abstraction principles.

Abstract

Many recent writers in the philosophy of mathematics have put great weight on the relative categoricity of the traditional axiomatizations of our foundational theories of arithmetic and set theory (\cite{Parsons1990a}, \cite{Parsons2008} \S{49}, \cite{McGee1997aa}, \cite{Lavine1999aa}, \cite{Vaananen2014aa}). Another great enterprise in contemporary philosophy of mathematics has been Wright's and Hale's project of founding mathematics on abstraction principles (\cite{Hale2001}, \cite{Cook2007aa}). In \cite{Walsh2012aa}, it was noted that one traditional abstraction principle, namely Hume's Principle, had a certain relative categoricity property, which here we term \emph{natural relative categoricity}. In this paper, we show that most other abstraction principles are \emph{not} naturally relatively categorical, so that there is in fact a large amount of incompatibility between these two recent trends in contemporary philosophy of mathematics. To better understand the precise demands of relative categoricity in the context of abstraction principles, we compare and contrast these constraints to (i) stability-like acceptability criteria on abstraction principles (cf. \cite{Cook2012aa}), (ii) the Tarski-Sher logicality requirements on abstraction principles studied by Antonelli \cite{Antonelli2010aa} and Fine~\cite{Fine2002}, and (iii) supervaluational ideas coming out of Hodes' work \cite{Hodes1984, Hodes1990aa, Hodes1991}.