Occam's razor

In philosophy, Occam's razor (also spelled Ockham's razor or Ocham's razor; Latin: novacula Occami) is the problem-solving principle that recommends searching for explanations constructed with the smallest possible set of elements. It is also known as the principle of parsimony or the law of parsimony (Latin: lex parsimoniae). Attributed to William of Ockham, a 14th-century English philosopher and theologian, it is frequently cited as Entia non sunt multiplicanda praeter necessitatem, which translates as "Entities must not be multiplied beyond necessity", although Occam never used those words. Popularly, the principle is sometimes paraphrased as "of two competing theories, the simpler explanation of an entity is to be preferred".

The philosophical razor advocates that when presented with competing hypotheses about the same prediction and both hypotheses have equal explanatory power, one should prefer the hypothesis that requires the fewest assumptions, and that this is not meant to be a way of choosing between hypotheses that make different predictions. Similarly, in science, Occam's razor is used as an abductive heuristic in the development of theoretical models rather than as a rigorous arbiter between candidate models.

History

The phrase Occam's razor did not appear until a few centuries after William of Ockham's death in 1347. Libert Froidmont, in his 1649 Philosophia Christiana de Anima (On Christian Philosophy of the Soul) claimed to have coined the phrase novacula occami when he described Gregory of Rimini, one of Ockham's critics. Ockham did not invent this principle, but its fame – and its association with him – may be due to the frequency and effectiveness with which he used it. Ockham stated the principle in various ways, but the most popular version – "Entities are not to be multiplied without necessity" (Non sunt multiplicanda entia sine necessitate) – was formulated by the Irish Franciscan philosopher John Punch in his 1639 commentary on the works of Duns Scotus.