OCCAM'S RAZOR

Principle of parsimony or principle of simplicity; One should always choose the simplest explanation of a phenomenon, the one that requires the fewest leaps of logic, or, Given a choice between two explanations, choose the simplest -- the explanation which requires the fewest assumptions. This principle is important in evaluating hypothes relating to conservation biology. It allows a logical assessment of the potential value of hypothesis thus giving a guide to resource use. It also allows conservationists to negate spurious speculative arguments.

The following text is quoted from the Encyclopaedia Britannica, Inc., 1994 web site.

http://www.britannica.com

"William (of) Ockham/Occam and Ockham's Razor
William of Ockham, also called William Ockham (Ockham also spelled " Occam") (1285-1347/49), was a medieval monk.. (a scholastic)

Ockham's razor, also spelled "Occam's razor", but also called "law of economy" or "law of parsimony", is a principle stated by William of Ockham, that entities are not to be multiplied beyond necessity (non sunt multiplicanda entia praeter necessitatem). This principle was, in fact, invoked before Ockham by Durand de Saint-Pourcain, a French Dominican theologian and philosopher of dubious orthodoxy, who used it to explain that abstraction is the apprehension of some real entity. Galileo did something similar by defending the simplest hypothesis of the heavens, and other later scientists stated similar simplifying laws and principles. It is called "Ockham's razor" because he mentioned the principle so frequently and employed it so sharply. For instance, he used it
1. to dispense with relations which he held to be nothing distinct from their foundation in things;
2. with efficient causality, which he tended to view merely as regular succession;
3. with motion, which is merely the reappearance of a thing in a different place;
4. with psychological powers distinct for each mode of sense;
5. and with the presence of ideas in the mind of the Creator, which are merely the creatures themselves."

The following site offers a comprehensive outline of philosophical concepts relating to Occam's Razor. http://pespmc1.vub.ac.be/

The following text is quoted from the above site

Principle of parsimony or principle of simplicity
F. Hetlighen, Principia Cybernetica Web, 1997.

Occam's razor is a logical principle attributed to the mediaeval philosopher William of Occam (or Ockham). The principle states that one should not make more assumptions than the minimum needed. This principle is often called the principle of parsimony. It underlies all scientific modelling and theory building. It admonishes us to choose from a set of otherwise equivalent models of a given phenomenon the simplest one. In any given model, Occam's razor helps us to "shave off" those concepts, variables or constructs that are not really needed to explain the phenomenon. By doing that, developing the model will become much easier, and there is less chance of introducing inconsistencies, ambiguities and redundancies.
Though the principle may seem rather trivial, it is essential for model building because of what is known as the "underdetermination of theories by data". For a given set of observations or data, there is always an infinite number of possible models explaining those same data. This is because a model normally represents an infinite number of possible cases, of which the observed cases are only a finite subset. The non-observed cases are inferred by postulating general rules covering both actual and potential observations.
For example, through two data points in a diagram you can always draw a straight line, and induce that all further observations will lie on that line. However, you could also draw an infinite variety of the most complicated curves passing through those same two points, and these curves would fit the empirical data just as well. Only Occam's razor would in this case guide you in choosing the "straight" (i.e. linear) relation as best candidate model. A similar reasoning can be made for n data points lying in any kind of distribution.
Occam's razor is especially important for universal models such as the ones developed in General Systems Theory, mathematics or philosophy, because there the subject domain is of an unlimited complexity. If one starts with too complicated foundations for a theory that potentially encompasses the universe, the chances of getting any manageable model are very slim indeed. Moreover, the principle is sometimes the only remaining guideline when entering domains of such a high level of abstraction that no concrete tests or observations can decide between rival models. In mathematical modelling of systems, the principle can be made more concrete in the form of the principle of uncertainty maximisation: from your data, induce that model which minimizes the number of additional assumptions.
This principle is part of epistemology, and can be motivated by the requirement of maximal simplicity of cognitive models. However, its significance might be extended to metaphysics if it is interpreted as saying that simpler models are more likely to be correct than complex ones, in other words, that "nature" prefers simplicity.