  Although medieval philosophers generally accept the distinction between relations secundum dici and relations secundum esse, and place heads and hands (and other body parts) in the former category, they sometimes disagree about the placement of certain other examples—most notably, knowledge and perception. Clearly, the names of these accidents are relative terms, since predications of the form ‘x is knowledge’ or ‘x is a perception’ are more perspicuously represented as of the form ‘x is knowledge of y’ and ‘x is a perception of y’. But should we characterize the accidents themselves as genuine relations (i.e., relations secundum esse)? Or should we rather say that they are qualities on which certain relations follow (i.e., relations secundum esse dici)? Near the end of Categories 7, Aristotle suggests an epistemic criterion that promises to resolve these questions. But because the criterion itself is difficult to understand, and there is no clear alternative to it, debate about these sorts of examples continues throughout the Middle Ages.