Then if you don't mind, I have a rather specific question regarding an essay by Harry Frankfurt from the recommended pre-reading collection on Free Will (Oxford, Gary Watson, Ed.). The essay's name is “Alternate Possibilities and Moral Responsibility”, and in it Frankfurt argues for a kind of compatibilism with regards to holding people morally responsible. He presents what he calls “the principle of alternate possibilities" which he states is “that a person is morally responsible for what he has done only if he could have done otherwise.”
The rest of Frankfurt's essay appears to play out as a decent example of Martinich's five-point outline. He discusses the principle described above, then goes into the effects of potential coercion on moral judgments. His argument appears to be that in a case where person A will cause person B to commit a crime if person B won't, but person B does anyway, then B both could not have done otherwise and also doesn't lose his moral culpability for the act.
Where Frankfurt loses me is his suggestion and ultimate conclusion, that the statement “that a person isn't morally responsible for what he has done only because he couldn't have done otherwise” is a correction to the previously stated principle, that “a person is morally responsible for what he has done only if he could have done otherwise.” It appears that all Frankfurt's done is to hypothesize "he couldn't have done otherwise" and demonstrate the validity of modus tollens.
This seemed so baldly trivial that I double and triple-checked the truth tables for “only because” as a logical connective to be sure. Even still, I assume I must not understand something, if for no other reason than the next few essays in Watson’s collection make no mention of this and I don't consider myself to be any more competent at criticism than Frankfurt's peers are. So my question to you, Jon, is simple: what am I missing here?