The music theory community has borne witness over the last decade to a proliferation of "similarity relations," tools designed to measure the similarity of pairs of pitch-class sets. It should be noted that most of these similarity relations are (a) fuzzy relations, not crisp ones, and (b) not similarity relations at all, since they lack the property of fuzzy transitivity required of similarity relations. A technique called "cluster analysis," borrowed from mathematical taxonomy, can be used to transform these "similarity relations" into similarity relations and to facilitate comparison of the relations to one another. As it turns out, most of these measures agree with one another about the basic topography of the world of pitch-class sets, in practice if not in theory, and what is more, they agree to a large extent with Allen Forte's theory of pitch-class set genera.