It is often held that, in contrast to Husserl, Heidegger's account of intentionality makes no essential reference to the first- person stance. This paper argues, on the contrary, that an account of the first- person, or 'subjectivity', is crucial to Heidegger's account of intelligibility and so of the intentionality, or 'aboutness' of our acts and thoughts, that rests upon it. It first offers an argument as to why the account of intelligibility in Division I of Being and Time, based on a form of third- person self-awareness, provides a necessary, but not a sufficient, condition for intentionality. It then shows that Heidegger provides a further necessary condition in his analysis of the collapse of the one-self in Division II. This condition is 'conscience', which is both a genuine first- person mode of self-awareness and, it is argued, the origin of reason as that which distinguishes factic 'grounds' from normative 'justifications'