 The widespread use of the term “sortal” definitely derives from Strawson, but readers should note that there are important differences among these authors. For a start, Strawson applies “sortal” to universals, Quine to predicates, and Wiggins to concepts. Thus, these authors illustrate the realist, nominalist, and conceptualist interpretations of sortals’ nature. Geach did not use the word “sortal” but most commentators identify his notion of a “substantival expression” with “sortal” in the other writers. Although Geach seems closest to Quine, since “expression” seems to be a linguistic notion, Geach generalizes his results across languages in ways that Quine would not find agreeable. These differences in usage among the four authors would not be important, if there were simple direct agreed upon relations among concepts, universals, and expressions. But there aren’t.