Ockham's Razor / Occam's Razor / Principle of Simplicity
Ockham's Razor
Biography
William of Ockham (also spelled Occam) was living in the Middle Ages (ca. 1285–1349). He was born in England in a town called Ockham near Ripley, Surrey. William devoted to a life in extreme poverty and minimalism and lived as a Franciscan friar and philosopher. He became a pioneer of nominalism, the position in metaphysics, that there exist no “universals” outside of the mind. Besides he was theologian, an outstanding logician and concentrated on epistemology and modern philosophy in general. [Carroll, 2005]
In 1324 he was suspected of heresy by Pope John XXII and spent four years under house arrest while his teaching and writing were being investigated. During this time Ockham even concluded that the Pope was a heretic. After massive dissensions between the Franciscan order and the papacy William fled to Munich and sought the protection of Emperor Louis IV of Bavaria. He spent much of the remainder of his life writing about political issues, including the relative authority and rights of the spiritual and temporal powers. He died in a convent in Munich, Bavaria. [Hoffmann et al., 1997]
Definition
One of the tools Ockham used routinely in his reasoning is what is known in philosophy as the principle of parsimony, and popularly as Ockham's Razor.
- Entities are not to be multiplied beyond necessity. Applied to systems of ontology or bodies of scientific theory, the principle encourages us to ask whether any proposed kind of entity is necessary. This principle of metaphysical economy retains influence in contemporary philosophy, although in judging rival systems it is not always clear which best meets the requirements of Ockham's Razor. [Bunnin and Tsui-James, 2005]
- "pluralitas non est ponenda sine necessitate"; "Entities should not be multiplied unnecessarily" or "Multiplicity ought not be posited without necessity". The principle that if two theories explain a phenomenon equally, the simpler theory requiring fewer assumptions and explanatory principles is preferred and that generalizations should be based on observed facts and not on other generalizations. One hallmark of pseudoscience is the requirement for many assumptions and untestable explanatory principles to support the core theories, which proponents often change when an assumption or principle is critically refuted. Under this principle, the theory containing testable components is preferred over the theory containing an inherently untestable component. [John Gay, 2005]
Rules/Conclusion
Rules
Just as for the Golden Rule, there are many ways of stating Ockham's Razor. Here are four that William of Ockham used in his works: [Hoffmann et al., 1997]
- It is futile to do with more what can be done with fewer. [Frustra fit per plura quod potest fieri per pauciora.]
- When a proposition comes out true for things, if two things suffice for its truth, it is superfluous to assume a third. [Quando propositio verificatur pro rebus, si duae res sufficiunt ad eius veritatem, superfluum est ponere tertiam.]
- Plurality should not be assumed without necessity. [Pluralitas non est ponenda sine necessitate.]
- No plurality should be assumed unless it can be proved (a) by reason, or (b) by experience, or (c) by some infallible authority. [Nulla pluralitas est ponenda nisi per rationem vel experientiam vel auctoritatem illius, qui non potest falli nec errare, potest convinci.]
Conclusion
In many cases this is interpreted as "keep it simple"', but in reality the Razor has a more subtle and interesting meaning. Suppose that you have two competing theories which describe the same system, if these theories have different predictions than it is a relatively simple matter to find which one is better: one does experiments with the required sensitivity and determines which one give the most accurate predictions. For example, in Copernicus' theory of the solar system the planets move in circles around the sun, in Kepler's theory they move in ellipses. By measuring carefully the path of the planets it was determined that they move on ellipses, and Copernicus' theory was then replaced by Kepler's. But there are are theories which have the very same predictions and it is here that the Razor is useful. Consider for example the following two theories aimed at describing the motion of the planets around the sun
- The planets move around the sun in ellipses because there is a force between any of them and the sun which decreases as the square of the distance.
- The planets move around the sun in ellipses because there is a force between any of them and the sun which decreases as the square of the distance. This force is generated by the will of some powerful aliens.
Since the force between the planets and the sun determines the motion of the former and both theories posit the same type of force, the predicted motion of the planets will be identical for both theories. the second theory, however, has additional baggage (the will of the aliens) which is unnecessary for the description of the system.
If one accepts the second theory solely on the basis that it predicts correctly the motion of the planets one has also accepted the existence of aliens whose will affect the behavior of things, despite the fact that the presence or absence of such beings is irrelevant to planetary motion (the only relevant item is the type of force). In this instance Ockham's Razor would unequivocally reject the second theory. By rejecting this type of additional irrelevant hypotheses guards against the use of solid scientific results (such as the prediction of planetary motion) to justify unrelated statements (such as the existence of the aliens) which may have dramatic consequences. In this case the consequence is that the way planets move, the reason we fall to the ground when we trip, etc. is due to some powerful alien intellect, that this intellect permeates our whole solar system, it is with us even now...and from here an infinite number of paranoid derivations.
For all we know the solar system is permeated by an alien intellect, but the motion of the planets, which can be explained by the simple idea that there is a force between them and the sun, provides no evidence of the aliens' presence nor proves their absence.
A more straightforward application of the Razor is when we are face with two theories which have the same predictions and the available data cannot distinguish between them. In this case the Razor directs us to study in depth the simplest of the theories. It does not guarantee that the simplest theory will be correct, it merely establishes priorities.
[Jose Wudka, 1998]
References
[Carrol, 2005] Robert Todd Carroll, Occam's razor, The Skeptic's Dictionnary, Created at: 2005, Retrieved at: October 24, 2005, http://skepdic.com/occam.html
[1] Nicholas Bunnin, E. P. Tsui-James, Glosario de términos filosóficos (en inglés), The Blackwell Companion to Philosophy, Retrieved at: October 24, 2005, http://www.filosofia.net/materiales/rec/glosaen.htm
[Gay, ] John Gay, Science Terminology, Washington State University, Updated at: July 15, 2005, http://www.vetmed.wsu.edu/courses-jmgay/GlossScience.htm
[Hoffmann et al., 1997] Roald Hoffmann, Vladimir I. Minkin, Barry K. Carpenter, Ockham's Razor and Chemistry, HYLE--International Journal for Philosophy of Chemistry, Vol. 3 (1997), Retrieved at: October 24, 2005, http://www.hyle.org/journal/issues/3/hoffman.htm
[4] Jose Wudka, What is Ockham's Razor?, Department of Physics, California, Created at: September 24, 1998, http://phyun5.ucr.edu/~wudka/Physics7/Notes_www/node10.html
[5] Scott Chase, Michael Weiss, Philip Gibbs, Chris Hillman, and Nathan Urban, What is Occam's Razor?, The Physics and Relativity FAQ, Updated at: July, 1997 by Sugihara Hiroshi, Original by Phil Gibbs September 1996, http://math.ucr.edu/home/baez/physics/General/occam.html
[6] Wikipedia-The Free Encyclopedia, William of Ockham, Updated at: October 11, 2005, http://en.wikipedia.org/wiki/William_of_Ockham