Philosophy
The Principle of Non-Contradiction
Quick fact
Aristotle first formally stated the principle of non-contradiction in his Metaphysics, calling it 'the most certain of all principles.' It cannot be proven without using itself, yet it is indispensable for any rational system.
Why this is interesting
You've probably heard someone say, 'That's a contradiction!'—but what makes a statement truly contradictory, and why can't reality allow it?