Ockham's Razor / Occam's Razor / Principle of Simplicity

From InfoVis:Wiki
Jump to navigation Jump to search

Ockham's Razor

Biography

William of Ockham

[Wikipedia, 2005]


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

Though most of Ockham's principles are enrooted in philosophy, many approaches (especially the principle of Simplicity) can be found in the basics of design principles.

  • Given a choice between functionally equivalent designs, the simplest design should be selected. Implicit in Ockham’s razor is the idea that unnecessary elements decrease a design’s efficiency, and increase the probability of unanticipated consequences. [Lidwell, 2004]
  • When comparing technologies that perform the same function, a technology that is simpler in design will tend to be simpler to construct and repair, but will tend to require greater skill to use, whereas a technology that requires less skill to use will tend to be more complex in design and more complex to construct and repair. For example, a straight razor is relatively simple in design and construction, but requires considerable skill to use, whereas an electric razor is relatively complex in design and construction but requires little skill to use. [Omick, 2005]

Examples

Example 1:

This example shows two different types of data visualization after a series of measurements of a property y in its response to adjustment of a factor x, with following results:

William of Ockham Some experimental measurements of a property y in response to variation of a factor x.

[Hoffmann et al., 1997]

William of Ockham William of Ockham

[Hoffmann et al., 1997]

Example 2:

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

[Wikipedia, 2005] Wikipedia-The Free Encyclopedia, William of Ockham, Last Updated at: November 03, 2005, http://en.wikipedia.org/wiki/Image:Occam.jpg

[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

[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

[Lidwell, 2004] Lidwell William, Universal Principles of Design, Created at: January 21, 2004, Retrieved at: October 24, 2005, http://www.visualgui.com/index.php?p=1

[Omick, 2005] David Omick, Living outside the box, A Few Simple Technologies for Daily Living, Design Considerations, Last Updated at: August 08, 2005, Retrieved at: October 24, 2005, http://www.omick.net/design/design.htm