Comparison is fundamental to the practice and subject-matter of philosophy, but has received scant attention by philosophers. This is even so in “comparative philosophy,” which literally distinguishes itself from other philosophy by being “comparative.” In this article, the need for a philosophy of comparison is suggested. What we compare with what, and in what respect it is done, poses a series of intriguing and intricate questions. In Part One, I offer a problematization of the tertium comparationis (the third of comparison) by examining conceptualizations of similarity, family resemblance, and analogy, which it is sometimes argued can do without a tertium comparationis. In Part Two, I argue that a third of comparison is already required to determine what is to be compared, and insofar as that determination precedes the comparison that tertium may be called “pre-comparative.” This leads me to argue against incomparability and to show how anything can indeed be compared to anything. In Part Three, I relate my arguments to what is today commonly labelled “comparative philosophy.” Finally, I raise some questions of ontology and politics in order to demonstrate the relevance of a philosophy of comparison.