Originally Posted by Achilles
Within moral philosophy, rules of logic can be used to determine "moral" vs "immoral" action.
Logic is applied to just about everything within philosophy, because it is a truth-preserving operation. Other than establishing validity, consistency and the like, it has no content on its own, it's more like a grammar.
That's why logic alone cannot be used to determine what a moral action is. For that, we'd need a set of premises as well and at least one of them would have to be normative to begin with, since we can't get any morals from purely descriptive/factual premises.
Now justifying those normative premises is quite the problem and that's where I think theistic theories have a disadvantage, as their premises involve a deity. (Which means that the plausibility of their premises is linked to the probability of the existence of that deity.. not a good thing if you ask me
) But the logical validity... well that's really a necessary requirement for any argument, if it's deductive. I'm sure there are theistic moral philosophies which are ok logically speaking.