Full Idea
The things we seek are equal in number to those we understand: the fact, the reason why, if something is, and what something is.
Gist of Idea
What we seek and understand are facts, reasons, existence, and identity
Source
Aristotle (Posterior Analytics [c.327 BCE], 89b24)
Book Reference
Aristotle: 'Posterior Analytics (2nd ed)', ed/tr. Barnes,Jonathan [OUP 1993], p.48