Full Idea
We think we know a thing only when we have grasped its first causes and principles and have traced it back to its elements.
Gist of Idea
We know a thing if we grasp its first causes, principles and basic elements
Source
Aristotle (Physics [c.337 BCE], 184a12)
Book Reference
Aristotle: 'Physics', ed/tr. Waterfield,Robin [OUP 1996], p.9
A Reaction
A nice Aristotelian analysis. It is hard to see what else you need to know about a thunderstorm, once you know what causes it, the principles which guide its operation, and the elements of which it is composed. But doesn't Aristotle seek its purpose…?