\documentclass[a4paper]{article} \usepackage{amssymb} \pagestyle{empty} \hoffset=-40pt \voffset=-20pt \textwidth 15.3cm \textheight 22cm % to fit our printers \begin{document} \begin{center}{\huge What Mathematical Truth Could Not Be-II\footnote{The work from which this talk is drawn is a review of issues arising out of the author's ``What Numbers Could Not Be'' ({\it Philosophical Review} 1965) and ``Mathematical Truth,'' ( {\it Journal of Philosophy} 1973) but principally out of the latter -- hence the title (one version of ``What Mathematical Truth Could Not Be-I'' appears in {\it Benacerraf and his critics}, A. Morton and S. Stich, eds., Blackwells, 1996).}}\end{center} \begin{center}{\large Paul Benacerraf}\end{center} \begin{center}{\large Princeton University}\end{center} \bigskip \large In a recent paper, ``Must we believe in set theory?''\footnote{Forthcoming in a collection of his papers, {\it Logic, logic and logic}, J. Burgess and R.C. Jeffrey, eds., Harvard University Press.} George Boolos declares that according to ZFC there exists a cardinal $\kappa$, which is equal to $\aleph_{\kappa}$, and is the limit of the sequence $\left\langle\aleph_0,\,\aleph_{\aleph_0},\, \aleph_{\aleph_{\aleph_0}},\,\dots\right\rangle$. That is (if it exists) $\kappa$ is the least ordinal greater than all of the $f(i)$, where $f(0)=\aleph_0$ and $f(i+1)=\aleph_{f(i)}$. To go directly to the source: ``...if $\kappa$ exists, there are at least as many as $\kappa$ sets. {\it Are} there so many sets?'' Boolos asks. It is, of course, uncontroversial that ZFC is committed to the existence of $\kappa$, just as it is committed to the existence of $\omega$. Boolos applauds the latter but seems to regard the former as an {\it over}commitment---a commitment with which he, personally, cannot go along. Any theory committed to the existence of {\it as many as} $\kappa$ things is simply not to be believed, on that ground alone. I take it that such a view is not uncontroversial---indeed that it is not even pellucid what the view {\it comes to}. I try in this talk to examine the reasons Boolos offers for it and, through them, how we should interpret the view and how defensible it might be to hold it. My focus throughout is, of course, not the belief specifically in $\kappa$ itself, but how this case illustrates certain tensions in our view of mathematical truth, meaning, and belief. \end{document}