Full Idea
Whatever is predicated in what something is is necessary.
Gist of Idea
The predicates of a thing's nature are necessary to it
Source
Aristotle (Posterior Analytics [c.327 BCE], 96b03)
Book Reference
Aristotle: 'Posterior Analytics (2nd ed)', ed/tr. Barnes,Jonathan [OUP 1993], p.64
A Reaction
This does NOT say that the essence is just the necessities. He goes on to say to say separately that certain properties of a triplet are part of the essence, as well as being necessary. This shows the nature of a thing is also necessary.