Also spelled:
Ockham’s razor
Also called:
law of economy or law of parsimony
Key People:
William of Ockham
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Occam’s razor, principle stated by the Scholastic philosopher William of Ockham (1285–1347/49) that pluralitas non est ponenda sine necessitate, “plurality should not be posited without necessity.” The principle gives precedence to simplicity: of two competing theories, the simpler explanation of an entity is to be preferred. The principle is also expressed as “Entities are not to be multiplied beyond necessity.”

The principle was, in fact, invoked before Ockham by Durandus of Saint-Pourçain, a French Dominican theologian and philosopher of dubious orthodoxy, who used it to explain that abstraction is the apprehension of some real entity, such as an Aristotelian cognitive species, an active intellect, or a disposition, all of which he spurned as unnecessary. Likewise, in science, Nicole d’Oresme, a 14th-century French physicist, invoked the law of economy, as did Galileo later, in defending the simplest hypothesis of the heavens. Other later scientists stated similar simplifying laws and principles.

Ockham, however, mentioned the principle so frequently and employed it so sharply that it was called “Occam’s razor” (also spelled Ockham’s razor). He used it, for instance, to dispense with relations, which he held to be nothing distinct from their foundation in things; with efficient causality, which he tended to view merely as regular succession; with motion, which is merely the reappearance of a thing in a different place; with psychological powers distinct for each mode of sense; and with the presence of ideas in the mind of the Creator, which are merely the creatures themselves.

William of Ockham, circa 1280 - 10.4.1349, English theologist and philosopher, portrait, later portrayal,
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Karl Popper

criterion of falsifiability, in the philosophy of science, a standard of evaluation of putatively scientific theories, according to which a theory is genuinely scientific only if it is possible in principle to establish that it is false. The British philosopher Sir Karl Popper (1902–94) proposed the criterion as a foundational method of the empirical sciences. He held that genuinely scientific theories are never finally confirmed, because disconfirming observations (observations that are inconsistent with the empirical predictions of the theory) are always possible no matter how many confirming observations have been made. Scientific theories are instead incrementally corroborated through the absence of disconfirming evidence in a number of well-designed experiments. According to Popper, some disciplines that have claimed scientific validity—e.g., astrology, metaphysics, Marxism, and psychoanalysis —are not empirical sciences, because their subject matter cannot be falsified in this manner.

This article was most recently revised and updated by Matt Stefon.
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