The thesis argues that, were there any moral obligations, they would be categorical; but there are no categorical requirements on action; therefore, there are no moral obligations. The underlying claim is that, because of this, morality itself rests on a mistaken view of normativity. The view of categoricity I provide rests on there being 'external reasons' for action. Having explained the connections between oughts (in particular the ought of moral obligation) and reasons for action in the first part of the thesis, I then develop and defend a version of reasons internalism that I call 'recognitional internalism'. The basic idea, which is not itself incompatible with categoricity, is that to have a reason one must be able to recognise that one has that reason. However, I work this basic claim into a substantive truth-condition for reason-statements and argue that the reasons one is able to recognise are controlled by one's subjective motives. I use this to argue that there are no categorical moral obligations. Nonetheless, I also argue that the substantive challenge internalism poses morality is importantly different, indeed more pressing, than usually thought. This is to justify the objective supremacy of the reasons for action constitutive of moral obligation.