first principles

A first principle is a foundational proposition that cannot be deduced from any other proposition. Aristotle defined it as “the first basis from which a thing is known.” It is where deduction begins and explanation terminates — not because we choose to stop, but because there is nowhere further to go.

The concept originates in Aristotle’s Posterior Analytics, where he argues that all demonstrative knowledge must rest on starting points that are themselves indemonstrable. If every truth required a prior truth to justify it, we’d face an infinite regress and could never know anything at all. First principles break this regress. They are known directly — through reason or perception — rather than derived through argument.

The most fundamental first principle is the law of non-contradiction: a thing cannot both be and not be in the same respect at the same time. Aristotle considered this the firmest of all principles, the one presupposed by every act of thought and speech. You cannot argue against it without already relying on it.

Ibn Sina made this point with characteristic bluntness. In The Metaphysics of The Healing, he wrote that those who deny the principle of non-contradiction should be flogged or burned until they admit that it is not the same thing to be burned and not burned, or whipped and not whipped. The argument is not rhetorical cruelty — it is a demonstration. The denier’s own flinching, their own distinction between pain and its absence, betrays an implicit grasp of the very principle they claim to reject. The body knows what the mouth denies.

In modern usage, “first-principles thinking” has been diluted into a vague gesture at thinking from scratch. But the original sense is more precise and more demanding. It is not merely the refusal to accept received wisdom. It is the identification of those truths so basic that denying them is incoherent — truths that make denial itself possible.