Occam’s Razor

In the mystery series post, I invoke Occam’s Razor. For those who are more interested, here is an explanation of Occam’s Razor from answer.com –

Occam’s Razor

Occam’s Razor (also Ockham’s Razor or any of several other spellings), is a principle attributed to the 14th century English logician and Franciscan friar, William of Ockham that forms the basis of methodological reductionism, also called the principle of parsimony.

In its simplest form, Occam’s Razor states that one should not make more assumptions than needed. When multiple explanations are available for a phenomenon, the simplest version is preferred. A charred tree on the ground could be caused by a landing alien ship or a lightning strike. According to Occam’s Razor, the lightning strike is the preferred explanation as it requires the fewest assumptions.

Variations

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 is not found in Ockham’s surviving writings. William wrote, in Latin, Pluralitas non est ponenda sine necessitate, which translates literally into English as “Plurality should not be posited without necessity”.

This can be interpreted in two subtly different ways. One is a preference for the simplest theory that adequately accounts for the data. Another is a preference for the simplest subset of any given theory which accounts for the data. The difference is simply that its possible for two different theories to explain the data equally well, but have no relation to one another. They share none of the same elements. Some would argue that in this case Occam’s Razor does not suggest a preference. Rather Occam’s Razor only comes into practice when a sufficient theory has something added to it which does not improve its predictive power. Occam’s Razor neatly cuts these additional theoretical elements away.

The principle of Occam’s Razor has inspired numerous expressions including: “parsimony of postulates”, the “principle of simplicity”, the “KISS principle” (keep it simple, stupid), and in some medical schools “When you hear hoofbeats, think horses, not zebras”.

A re-statement of Occam’s Razor, in more formal terms, is provided by information theory in the form of minimum message length.

Another variant of this law is Thargola’s Sword from Nightfall, (originally a short story by Isaac Asimov and later expanded to a novel in conjunction with Robert Silverberg):

We must drive a sword through any hypothesis that is not strictly necessary.

Leonardo da Vinci (1452–1519) lived after Ockham’s time and has a variant of Occam’s razor. His variant short-circuits the need for sophistication by equating it to simplicity.

Simplicity is the ultimate sophistication.

Occam’s Razor is now usually stated as follows:

Of two equivalent theories or explanations, all other things being equal, the simpler one is to be preferred.

As this 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.