Full Idea
The potential occurs when it is not necessary that its contrary be false. For example, it is potential that a man should be seated, since it is not false of necessity that he is not seated.
Gist of Idea
Possibility is when the necessity of the contrary is false
Source
Aristotle (Metaphysics [c.324 BCE], 1019b26)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.133
A Reaction
This is the standard point in modal logic that possibly is equivalent to not-necessarily-not (◊p → ¬□¬p).