Ockham’s razor (also spelled Occam’s razor) — A principle of parsimony holding that one should not posit more entities or explanations than necessary. It is associated with William of Ockham (c. 1287–1347), but the famous formula, entia non sunt multiplicanda praeter necessitatem (“entities must not be multiplied beyond necessity”), does not appear literally in his works. According to the historical literature, the later Latin formulation goes back to the Irish Scotist John Punch, in his commentary on the works of Duns Scotus (1639), who presents it as a common axiom among the Scholastics; the name “razor” is later still than Ockham himself. What one does find in Ockham are close formulations, such as numquam ponenda est pluralitas sine necessitate (“plurality must never be posited without necessity”), cited in the secondary literature from his commentary on Peter Lombard’s Sentences. The idea, however, is old and has precedents in Aristotle and the Scholastic tradition. In Ockham the principle works within his nominalism: since singular individuals and the signs that designate them suffice, it would be superfluous to posit universals as real entities, as the realists, Duns Scotus among them, did. In modern science, parsimony is a criterion for choosing between hypotheses (for example, Newton’s rules of reasoning in the Principia, 1687) and figures in debates about simplicity and inference to the best explanation. Note that it is a methodological maxim, not a law: the simplest hypothesis is not thereby necessarily true, and there is controversy about what counts as “simple,” fewer entities or fewer kinds of entities.
See also: Duns Scotus, Aristotle, Metaphysics.
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