Aristotle defined first principles as the foundational, self-evident, and indemonstrable truths from which all other knowledge is derived. These are the most basic truths that cannot be deduced from any other proposition. And since they are self-evident, they do not require further proof.

Aristotle believed that first principles were discovered through the process of induction. This gave rise to a kind of thought process that is now known as first principle thinking. This process involves iteratively breaking down problems into smaller and smaller pieces until you’re left to most essential phenomenas and truths. At this point you stop since these most essential truths are the first principle truths that require no further evidence.

Earliest known use of the first principle thinking goes back to Euclid’s work on Elements. Euclid used axiomatic thinking to develop most sophisticated geometric proofs that we use even today.