(or Ockham), 1285-1349?), known as Doctor Invincibilis (Latin, unconquerable doctor) and Venerabilis Inceptor (Latin, worthy initiator), English philosopher and Scholastic theologian, who is considered the greatest exponent of the nominalist school, the leading rival of the Thomist and Scotist schools.
Ockham was born in Surrey, England. He entered the Franciscan order and studied and taught at the University of Oxford from 1309 to 1319. Denounced by Pope John XXII for dangerous teachings, he was held in house detention for four years (1324-28) at the papal palace in Avignon, France, while the orthodoxy of his writings was examined. Siding with the Franciscan general against the pope in a dispute over Franciscan poverty, Ockham fled to Munich in 1328 to seek the protection of Louis IV, Holy Roman emperor, who had rejected papal authority over political matters. Excommunicated by the pope, Ockham wrote against the papacy and defended the emperor until the latter's death in 1347. The philosopher died in Munich, apparently of the plague, while seeking reconciliation with Pope Clement VI.
Ockham won fame as a rigorous logician who used logic to show that many beliefs of Christian philosophers (for example, that God is one, omnipotent, creator of all things; and that the human soul is immortal) could not be proved by philosophical or natural reason but only by divine revelation. His name is applied to the principle of economy in formal logic, known as Ockham's razor, which states that entities are not to be multiplied without necessity.
Occam's teachings mark an important break with previous medieval philosophy. Adhering to the position of NOMINALISM, he rejected the Aristotelian REALISM of St. Thomas Aquinas, specifically denying the existence of universals except in people's minds and language. He disputed the self-evidence of the Aristotelian final cause and of the existence of God, denying the competence of reason in matters of faith. This led him to hold that logic can be studied outside the province of metaphysics, a position that proved important in the development of scientific enquiry. In logic, Occam is remembered for his use of the principle of parsimony, formulated as "Occam's razor," which enjoined economy in explanation with the axiom "It is vain to do with more what can be done with less."
Sometimes you can find another version of Occam's razor: "Entia non sunt multiplicanda praeter necessitatem". Similar forms are found in the writings of his teacher Duns Scotus. You can even get Aristotle in the Physics (book I, chapter vi) saying things like `for the more limited, if adequate, is always preferable'. Or in (book VIII, chapter vi) `for if the consequences are the same it is always better to assume the more limited antecedent'.
A rule in science and philosophy stating that entities should not be multiplied needlessly. This rule is interpreted to mean that the simplest of two or more competing theories is preferable and that an explanation for unknown phenomena should first be attempted in terms of what is already known. Also called law of parsimony.
The principle underlies all scientific modelling and theory building. It admonishes us to choose from a set of otherwise equivalent models of a given phenomenon the simplest one. In any given model Occam's razor helps us to "cut away" those concepts, variables or constructs that are not really needed to explain the phenomenon. By doing that, developing the model will become much easier, and there is less chance of introducing inconsistencies, ambiguities and redundancies.
Occam's razor is especially important for universal models such as the ones developed in General Systems Theory, mathematics or philosophy, because there the subject domain is of an unlimited complexity. If one starts with too complicated foundations for a theory that potentially encompasses the universe, the chances of getting any manageable model are very slim indeed. Moreover, the principle is sometimes the only remaining guideline when entering domains of such a high level of abstraction that no concrete tests or observations can decide between rival models.