Which medieval English friar is credited with the principle known as Occam's razor?

William of Ockham is the medieval English friar credited with the principle known as Occam’s razor. The principle favors explanations that avoid unnecessary assumptions when competing explanations account for the same evidence equally well.

Ockham was an English Franciscan friar, theologian, philosopher, and logician who lived around 1287–1347. He used several formulations of the idea in his writings, including the claim that plurality should not be posited without necessity. The modern phrase “Occam’s razor,” however, appeared centuries after his death.

The principle did not originate entirely with Ockham. Similar ideas can be traced to Aristotle, Ptolemy, Robert Grosseteste, and John Duns Scotus. Ockham became its most famous medieval advocate because he applied parsimony systematically to logic, metaphysics, theology, and natural philosophy. A common mistake is to treat the razor as a rule that the simplest explanation is always true. It is better understood as a preference between explanations with comparable explanatory power, not proof that reality must be simple.