a repository of mathematical know-how

Use Occam's razor

Quick description

Occam's razor is the principle enunciated by William of Ockham (English logician 1285–1349) that "entities must not be multiplied beyond necessity". This is particularly important in the description of the physical world, and in modeling. For example, the number of parameters and dimensionality of a model should be kept to a minimum.


Example 1

In the modeling of air flow in meteorology, it is common to assume that air is incompressible, although it clearly is not. The reasons for this are

  • the velocities and pressure differences involved are low and do not contribute greatly to the predictions, and

  • including compressibility would introduce sound waves making the problem hyperbolic and complicating numerical simulation (e.g., requiring that time-steps satisfy a Courant–Friedrichs–Levy conditions).

General discussion


Inline comments

The following comments were made inline in the article. You can click on 'view commented text' to see precisely where they were made.

Is this really an example of

Is this really an example of Occam's razor? It's not 'needless' to hypothesize that air is compressible - after all, it is (slightly) compressible - it just leads to intractable equations!