Ed asked:

What's Ockham's Razor? and when is it commonly used in testing an empirical hypothesis?

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Before all else, you need to be clear in your mind that Ockam's Razor is not being 'used' for anything.
Although there seems to be a widespread but fairly vague belief that it's some kind of methodology
(or even a real razor!), it isn't. In fact, it goes back to (of course) William Ockham, the scholastic
philosopher, who wrote on two separate and quite unrelated occasions in pithy epigrammatic form
words to the effect that 'if you are confronted with a choice of two equally valid alternatives, take the
simpler'. The reason being, essentially, that humans are error prone, and by taking the simpler
alternative, you also reduce the chance of compounding errors. You can also apply the precept to
situations where there are no alternatives, but just a very complicated setup. Then you are advised to
seek ways of simplifying it. This simplification, which you may picturesquely imagine as trimming off
the curls in your beard, so that it's lean and clean, is probably what most people would think of as
'Ockam's Razor'.

From this you will gather that Ockam's Razor is just a very good precept. It's got nothing to do with
science at all, except that many scientists have adopted it as a general sort of advice that seems
especially pertinent to their pursuits. But I would not be surprised if some scientific theorist has
worked out a true methodology based on this principle. I'm not aware of any such explicit
methodology, but even if there is one, it evidently has no bearing on Ockam himselfno more than,
say, the old adage 'birds of a feather flock together' has anything to do with the science of
ornithology.

Jürgen Lawrenz

Sydney