Virtues of Scientific Theories

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Criteria for Distinguishing Theories
There can be indefinitely many theories which fulfill the criteria of the deductive nomological method with falsificationism. How do we choose among them? These are listed in order of importance: earlier virtues trump later ones.

1. Predictive power: the more that a theory can successfully predict, the better it is.
   
   
2. Coherence with Existing Theory: all other things being equal, the theory that coheres with (does not contradict) other successful theories is preferable to one that does contradict them.
   
   
3. Simplicity: all other things being equal, the simpler theory is preferable. (This is very controversial, since there is debate about what simplicity is. I believe that there is a good measure, called Kolmogorov complexity. The reason simpler theories are preferable is primarily because they appear more likely to be true; they may also be easier to use.)

An Example
The following is a sticker being put on high school biology texts. There are at least two implicit mistakes here; one based upon a misunderstanding of scientific method and what "theory" means for that method; and the other a confusion about the meaning of "fact" and the relation of facts to theory. Can you identify them?

This textbook contains material on evolution. Evolution is a theory, not a fact, regarding the origin of living things. This material should be approached with an open mind, studied carefully and critically considered.