"What is 'Occam's Razor?'''

% of readers think this story is Fact. Add your two cents.

“What is ‘Occam’s Razor?”’
by Wikipedia

“Occam’s razor, also Ockham’s razor, is a principle attributed to 14th-century English logician and Franciscan friar, William of Ockham. The principle states that the explanation of any phenomenon should make as few assumptions as possible, eliminating those that make no difference in the observable predictions of the explanatory hypothesis or theory. The principle is often expressed in Latin as the lex parsimoniae (“law of parsimony”, “law of economy”, or “law of succinctness”): entia non sunt multiplicanda praeter necessitatem, roughly translated as “entities must not be multiplied beyond necessity.” An alternative version Pluralitas non est ponenda sine necessitate translates “plurality should not be posited without necessity.”

When multiple competing hypotheses are equal in other respects, the principle recommends selecting the hypothesis that introduces the fewest assumptions and postulates the fewest entities. It is in this sense that Occam’s razor is usually understood.

Originally a tenet of the reductionist philosophy of nominalism, it is more often taken today as a heuristic maxim (rule of thumb) that advises economy, parsimony, or simplicity, often or especially in scientific theories. Here the same caveat applies to confounding topicality with mere simplicity. (A superficially simple phenomenon may have a complex mechanism behind it. A simple explanation would be simplistic if it failed to capture all the essential and relevant parts.)

Prior to the 20th century, it was a commonly-held belief that nature itself was simple and that simpler hypotheses about nature were thus more likely to be true; this notion was deeply rooted in the aesthetic value simplicity holds for human thought and the justifications presented for it often drew from theology. Thomas Aquinas made this argument in the 13th century, writing, “If a thing can be done adequately by means of one, it is superfluous to do it by means of several; for we observe that nature does not employ two instruments where one suffices.”

The common form of the razor, used to distinguish between equally explanatory hypotheses, can be supported by appeals to the practical value of simplicity. Hypotheses exist to give accurate explanations of phenomena, and simplicity is a valuable aspect of an explanation because it makes the explanation easier to understand and work with. Thus, if two hypotheses are equally accurate and neither appears more probable than the other, the simple one is to be preferred over the complicated one, because simplicity is practical.

Beginning in the 20th century, epistemological justifications based on induction, logic, pragmatism, and probability theory have become more popular among philosophers.

One way a theory or a principle could be justified is empirically; that is to say, if simpler theories were to have a better record of turning out to be correct than more complex ones, that would corroborate Occam’s razor. However, Occam’s razor is not a theory in the classic sense of being a model that explains physical observations, relying on induction; rather, it is a heuristic maxim for choosing among such theories and underlies induction. Justifying such a guideline against some hypothetical alternative thus fails on account of invoking circular logic.

To wit: There are many different ways of making inductive inferences from past data concerning the success of different theories throughout the history of science, and inferring that “simpler theories are, other things being equal, generally better than more complex ones” is just one way of many- which only seems more plausible to us because we are already assuming the razor to be true. This, however, does not exclude legitimate attempts at a deductive justification of the razor (and indeed these are inherent to many of its modern derivatives). Failing even that, the razor may be accepted a priori on pragmatist grounds.”

- http://en.wikipedia.org/wiki/Occam’s_razor