Occam´s Razor

Occam's razor (or Ockham's razor) often expressed in Latin as the lex parsimoniae, translating to law of parsimony, law of economy or law of succinctness, is a principle that generally recommends, when faced with competing hypotheses that are equal in other respects, selecting the one that makes the fewest new assumptions.

The principle was often inaccurately summarized as "the simplest explanation is most likely the correct one." This summary is misleading, however, since in practice the principle is actually focused on shifting the burden of proof in discussions. That is, the razor is a principle that suggests we should tend towards simpler theories until we can trade some simplicity for increased explanatory power. Contrary to the popular summary, the simplest available theory is sometimes a less accurate explanation. Philosophers also add that the exact meaning of "simplest" can be nuanced in the first place.

Bertrand Russell offered what he called "a form of Occam's Razor" which was "Whenever possible, substitute constructions out of known entities for inferences to unknown entities."
Occam's razor is attributed to the 14th-century English logician, theologian and Franciscan friar Father William of Ockham (d'Okham) although the principle was familiar long before. The words attributed to Occam are "entities must not be multiplied beyond necessity" (entia non sunt multiplicanda praeter necessitatem), although these actual words are not to be found in his extant works. The saying is also phrased as pluralitas non est ponenda sine necessitate ("plurality should not be posited without necessity"). To quote Isaac Newton, "We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. Therefore, to the same natural effects we must, so far as possible, assign the same causes."

In science, Occam’s razor is used as a heuristic (general guiding rule) to guide scientists in the development of theoretical models rather than as an arbiter between published models. In the scientific method, Occam's razor is not considered an irrefutable principle of logic, and certainly not a scientific result.
In 2005, Marcus Hutter mathematically proved[ that shorter computable theories have more weight when calculating the expected value of an action across all computable theories which perfectly describe previous observations (universal artificial intelligence).