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Razoring Ockham’s razor

Occam's RazorMassimo Pigliucci at Rationally Speaking writes:

Frustra fit per plura quod potest fieri per pauciora. [It is futile to do with more things that which can be done with fewer] (Summa Totius Logicae)

Philosophers often refer to this as the principle of economy, while scientists tend to call it parsimony. Skeptics invoke it every time they wish to dismiss out of hand claims of unusual phenomena (after all, to invoke the “unusual” is by definition unparsimonious, so there).

There is a problem with all of this, however, of which I was reminded recently while reading an old paper by my colleague Elliot Sober, one of the most prominent contemporary philosophers of biology. Sober’s article is provocatively entitled “Let’s razor Ockham’s razor” and it is available for download from his web site.

Let me begin by reassuring you that Sober didn’t throw the razor in the trash. However, he cut it down to size, so to speak. The obvious question to ask about Ockham’s razor is: why? On what basis are we justified to think that, as a matter of general practice, the simplest hypothesis is the most likely one to be true?

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