The Naturalistic Fallacy, and Euthyphro

The naturalistic fallacy is when you invalidly infer facts about what ought to be the case only from facts about what is the case. ("only" because facts about what is the case can, of course, be relevant to what one ought to do! They just can't be the whole story)

So, one implication is that, even if people are psychologically, culturally, evolutionarily or neurologically wired up to do something, this doesn't show that this thing is right. Perhaps people are just wired up in ways that they shouldn't be.

It struck me the other day that this fits in well with the Euthyphro dilemma. Recall:
Either (a) God decides what is good, or (b) goodness is fixed independently of God's will and he merely passes on his knowledge of it to us.

The problem with (a) is precisely that it is an instance of the naturalistic fallacy. Sure, God might command X, but this is a fact about what is the case, not a fact about what ought to be the case. In order to move from "God commands X" to "you ought to do X", we need the premise "You ought to do whatever God commands". And this premise cannot be secured by God without circularity, and so we're forced onto horn (b), that some facts about what you ought to do are fixed independently of God.

That, of course, is not something an omnipotent God can live with.