 The differences among these views can be illustrated by comparing their respective diagnoses of a fictional Caligula whose state of mind is completely coherent but who values torturing people for fun (Street 2010: 371). For realists, he is in error about some true moral value. There are some reasons—for example, the reason not to torture others for fun—that we have quite independently of our evaluative attitudes and practical reasoning. Kantians agree with realists that fictional Caligula has no good reasons for torturing anyone, but differ in explaining why this is so. Some Kantians think that fictional Caligula is incoherent, even though not obviously so. His incoherence can be shown by spelling out the norms that are constitutive of valuing. Such constitutive norms entail valuing humanity, and this shows that fictional Caligula is making a mistake by his own lights, even though he may never fully realize this, due to poor reflection, ignorance of the non-normative facts or some other limitation (Korsgaard 1996a: 121–123). A different Kantian argument establishes that an internally coherent Caligula is conceivable, that is, he can be thought without contradiction, but his case is blocked by general facts about moral sensibility (Engstrom 2009: 243, § III.7, Bagnoli 2009). Such a Caligula would have no reason to torture others. By contrast, Humean constructivists hold that an internally coherent Caligula is possible and that such a person has reasons for torturing others (Street 2009).