Internalists about reasons following Bernard Williams claim that an agent’s normative reasons for action are constrained in some interesting way by her desires or motivations. In this paper, I offer a new argument for such a position—although one that resonates, I believe, with certain key elements of Williams’ original view. I initially draw on P.F. Strawson’s famous distinction between the interpersonal and the objective stances that we can take to other people, from the second-person point of view. I suggest that (...) we should accept Strawson’s contention that the activity of reasoning with someone about what she ought to do naturally belongs to the interpersonal mode of interaction. I also suggest that reasons for an agent to perform some action are considerations which would be apt to be cited in favor of that action, within an idealized version of this advisory social practice. I then go on to argue that one would take leave of the interpersonal stance towards someone—thus crossing the line, so to speak—in suggesting that she do something one knows she wouldn’t want to do, even following an exhaustive attempt to hash it out with her. An internalist necessity constraint on reasons is defended on this basis. (shrink)