Full Idea
The question 'what is it?' refers to the persistence and lifespan of an entity, and so manifests the identity over time of an entity and its persistence, between persistence and existence, and between its existence and being the kind of thing it is.
Gist of Idea
'What is it?' gives the kind, nature, persistence conditions and identity over time of a thing
Source
David Wiggins (Sameness and Substance [1980], 2.1)
Book Reference
Wiggins,David: 'Sameness and Substance' [Blackwell 1980], p.54
A Reaction
The idea that establishing the kind of a thing can do all this work strikes me as false. The lifespan of a 'human' can be between five minutes and a hundred years. Humans have a clear death, but thunderstorms don't.