Full Idea
Although what-is-it [ti esti] questions serve the classificatory project in 'Categories', they are no help in the causal enquiries of 'Metaphysics' Z.17. The essence of interest can't be the species or the differentia-cum-genus complex.
Gist of Idea
'Categories' answers 'what?' with species, genus, differerentia; 'Met.' Z.17 seeks causal essence
Source
report of Aristotle (Metaphysics [c.324 BCE], 1041a05-b36) by Michael V. Wedin - Aristotle's Theory of Substance X.4
Book Reference
Wedin,Michael V.: 'Aristotle's Theory of Substance' [OUP 2000], p.421
A Reaction
Wedin's view is that these are compatible. The implication is that the nature of essence depends entirely on what it is you want to explain. Explain the category, or explain the behaviour?