Second, it seems that one can have intentions based on false beliefs without being instrumentally irrational, or irrational in any other way.  Instrumental rationality, as it’s usually understood, is a requirement of coherence governing one’s intentions and beliefs—a requirement that is in place regardless of the truth of those beliefs.  The person who intends to get to Memphis, believes that he must intend to stay on 95N to get there, and does intend to stay on 95N, displays coherence in his attitudes, despite having a false belief.  So, an accusation of instrumental irrationality here would be misplaced. (Additionally, it would also be inappropriate to accuse him of any theoretical irrationality, if we suppose that this belief isn’t inconsistent with any other beliefs he holds, and he also believes there’s conclusive evidence for it, and so forth.)  Hume would have to conclude either that such cases are impossible, or that they involve instrumental irrationality. 