Full Idea
If demonstrative understanding proceeds from necessary principles, and whatever holds of an object in itself is necessary, then it is clear that demonstrative deductions will proceed from certain items of this sort.
Gist of Idea
Demonstrative understanding rests on necessary features of the thing in itself
Source
Aristotle (Posterior Analytics [c.327 BCE], 74b05-)
Book Reference
Aristotle: 'Posterior Analytics (2nd ed)', ed/tr. Barnes,Jonathan [OUP 1993], p.10
A Reaction
This is the characterization of the essence of something in terms of what counts as a good explanation of that thing. Although explanation is a bit subjective, I like this approach, because you will dig down to the source of the powers of the thing.