Aquinas and quantifier mistakes

Abstract

In his “Third Way” Aquinas appears to argue in a way that relies upon shifting quantifiers in a fallacious way. Some have tried to save this and other parts of the “Third Way” by introducing sophisticated logical and metaphysical machinery. Alternatively, Aquinas’ apparently fallacious quantifier shift can be seen to be part of a valid argument if we supply a simple premise which an Aristotelian natural philosopher would surely hold. In this short paper, I consider candidates for this premise, defend a specific premise, and from that discussion draw a moral about quantifier predicate logic. I conclude that Aristotelian natural philosophy is more than an historical backdrop to Aquinas’ arguments.