  In addition to categorial kinds such as the sophist and statesman, there are also the great kinds discussed in the  Sophist—change, rest, being, sameness, and difference.  These kinds were embraced in the Parmenides (esp.  Parmenides 130b), but they seem markedly  different from ordinary kinds like the sophist and statesman. The  vowel forms—being, sameness, and difference—appear to  structure other kinds, enabling them to be what they are and to  relate to one another. Dialectic aims to discover and articulate  those structures. Structural kinds are closely tied to dialectic, as  Parmenides foretold, but both forms and dialectic seem to have  developed apace since the Phaedo and the Republic.