Occam's Razor
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KISS for Occam's Razor
Occam's Razor
Occam's Razor (also Ockham's Razor), is a principle attributed to the 14th century logician and Franciscan friar, William of Ockham that forms the basis of methodological reductionism. It is nowadays usually stated as follows: "Of two competing theories or explanations, all other things being equal, the simpler one is to be preferred." When that is ambiguous, Isaac Newton's version may be better: "We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances." In modern usage, "true" may mean "well established."
The principle is most often expressed as Entia non sunt multiplicanda praeter necessitatem, or "Entities should not be multiplied beyond necessity", but this sentence was written by later authors and cannot be found in his surviving writings. William wrote the Latin Pluralitas non est ponenda sine neccesitate, which translates literally into English as "Plurality should not be posited without necessity".
Dave Beckett of the University of Kent at Canterbury writes: "The medieval rule of parsimony, or principle of economy, frequently used by Ockham came to be known as Ockham's razor."
Occam's Razor has also been referred to as "parsimony of postulates" and the "principle of simplicity" and "K.I.S.S." (keep it simple, stupid). Another proverb expressing the idea that is often heard in medical schools is "When you hear hoofbeats, think horses, not zebras."
In fiction: another variant of this law is Thargola's Sword from Nightfall, written by Isaac Asimov and Robert Silverberg: "We must drive a sword through any hypothesis that is not strictly necessary".
Science and Occam's Razor
Occam's Razor has become a basic principle of the scientific method. It is important to note that it is a heuristic argument that does not necessarily give correct answers; it is a loose guide to the scientific hypothesis which contains the least possible number of unproven assumptions and is the most likely to be fruitful. Often, several hypotheses are equally "simple" and Occam's Razor does not express any preference in these cases.
For example, after a storm you notice that a tree has fallen. Based on the evidence of "a storm" and "a fallen tree" a reasonable hypothesis would be that "the storm blew down the tree" -- a hypothesis that requires only one assumption--that it was, in fact, a strong wind that knocked over the tree, rather than a meteor or an elephant. The hypothesis that "the tree was knocked over by marauding 200 meter tall space aliens" requires several additional assumptions (concerning the very existence of aliens, their ability and desire to travel interstellar distances and the alien biology that allows them to be 200 meters tall in terrestrial gravity) and is therefore less preferable.
Occam's Razor is not equivalent to the idea that "perfection is simplicity". Albert Einstein had this in mind when he wrote in 1933 that "The supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience" often paraphrased as "Theories should be as simple as possible, but no simpler." It often happens that the best explanation is much more complicated than the simplest explanation because it requires fewer assumptions. Some people have oversimplified Occam's Razor as "The simplest explanation is the best." (or is "the true one")