Principle of sufficient reason

The principle of sufficient reason or PSR is often formulated as the claim that every contingent fact has a sufficient reason. It is sometimes interpreted as the stronger claim, that everything has a cause, for example within a deterministic system of universal causation. Necessary truths are generally regarded as not requiring a cause, since causation presupposes contingency, though they may still be said to have a sufficient reason or explanation in virtue of their necessity. Confusion may arise when using the words "reason" and "cause" interchangeably.

A sufficient reason is sometimes described as the coincidence of every single thing that is needed for the occurrence of an effect. The principle is relevant to Munchausen's trilemma, as it seems to suppose an infinite regress, rather than a foundational brute fact. The principle was articulated and made prominent by Gottfried Wilhelm Leibniz. Arthur Schopenhauer wrote On the Fourfold Root of the Principle of Sufficient Reason.