  The central section of the Sophist has been much discussed and remains controversial. The distinction between consonant and vowel forms concerns the way kinds relate to other kinds, but different types of forms usually play these two roles. Consonant forms have categorial content—that is, they can be organized into genus-species trees, like entities in Aristotle’s Categories and like the kinds in the earlier divisions in the Sophist. Vowel forms are empty of categorial content but have structural content, and the greatest of the great kinds apply to everything. Philosophers in the Middle Ages would call such kinds transcendentals, since they transcend Aristotle’s ten categories (substance, quantity, quantity, and the other categories); Gilbert Ryle called them syncategorematic. These entities are not highly general kinds—viewed as such, they would be categorial, since highest genera have (very general) categorial content. In Ryle’s words, the vowel forms “function not like the bricks but like the arrangement of the bricks in a building” (Ryle 1939 [1965], esp. 131, 143–44). They structure other kinds and enable them to relate to one another. Let us call them structural kinds (do not take the label to suggest that categorial kinds lack structure, only that structural kinds are purely structural and derive categorial content through their applications).