  The problem, in short is this. In order to be valid, “sufficient causal condition” must be used in the same sense throughout the argument. If “causally sufficient condition” is taken in the weak sense, however, then the inferences from 4 to 5, and from 6 to 7, are illegitimate. Yet if “casually sufficient condition” is taken in the strong sense, there are reasons to believe that its first premise is false. In either case, the argument is unsound.