Full Idea
What is necessary cannot be otherwise.
Gist of Idea
What is necessary cannot be otherwise
Source
Aristotle (Posterior Analytics [c.327 BCE], 88b32)
Book Reference
Aristotle: 'Posterior Analytics (2nd ed)', ed/tr. Barnes,Jonathan [OUP 1993], p.45
A Reaction
If the next interesting question is the source of necessity, then the question seems to be 'what prevents it from being otherwise?'.