Occam’s razor

Occam’s Razor (also called Ockham’s Razor) refers to a principle of parsimony or simplicity in modern science associated with the medieval monk William of Ockham. His principle states: “Entities should not be multiplied unnecessarily.”

The word “entities” is ambiguous here: what should be minimized, the total number of entities of any kind or the number of kinds of entity? The Stanford Encyclopedia of Philosophy (SEP) article on “Simplicity” notes:

The default reading of Occam’s Razor in the bulk of the philosophical literature is as a principle of qualitative parsimony.

The distinction between qualitative and quantitative here is between the number of types (or kinds) of entities postulated and the number of individual entities postulated. So Occam’s Razor has no problem with a zillion atoms all alike but it does have a problem with two or more different kinds of atoms.

The SEP article notes:

It should be noted that interpreting Occam’s Razor in terms of kinds of entity brings with it some extra philosophical baggage of its own. In particular, judgments of parsimony become dependent on how the world is sliced up into kinds.

So Occam’s Razor prefers one kind of parsimony: qualitative parsimony. For science this means theories that posit fewer kinds of entity are preferred. This is as arbitrary as preferring theories positing fewer entities but more kinds of entity.

It is basically the standard classification problem: which is better, lumping or splitting? Occam’s Razor prefers lumping into fewer classes. But there is no necessary reason for this preference. It is arbitrary and biased.

This preference has direct implications for what kind of theories are selected in science. For example, an explanation in geology in terms of uniform processes is preferred over one that also includes global catastrophes. And an evolutionary theory which considers all life to be one kind of entity over a long time is preferred over any theory that posits multiple kinds of life over a shorter time.

This principle is biased and should be rejected or changed.