In this dissertation, I argue for a set of interpretations regarding the relationship between moral obligation and reasons for acting in the theories of Hobbes, Hutcheson, and Hume. Several commentators have noted affinities between these naturalist moral theories and contemporary ethical internalism. I argue that attempts to locate internalist theses in these figures are not entirely successful in any clear way. I follow Stephen Darwall's suggestion that addressing the question “why be moral?” is one of the fundamental problems of modern (...) moral philosophy. Since, as some have argued, there is a tension between accepting internalism and providing an adequate response to the “why be moral” question, I argue that each figure maintains a distinctive response to this question given the sort of internalism, if any, he would accept. In the introduction, I provide the key distinctions that arise from contemporary discussions of ethical internalism, and I motivate my project of looking for insight into the relationship between internalism and amoralism in the British Moralists. Chapters 1 and 2 focus on the moral theory Hobbes who, I argue, would accept a version of constitutive existence internalism because he holds that there is a necessary connection between one's being contractually obligated and one's being in certain rationally motivating states. I then present the fool's objection as an objection to the assumption of a relevant similarity between divine obligation and contractual obligation. I argue that, irrespective of this dissimilarity, the fool has some rational motive to keep his covenants in virtue of the fact that making covenants changes one's decision situation in such a way that it becomes reasonable to treat covenants as if they imposed categorical constraints on behavior. I claim that Hobbes's response to the fool is, at least in part, that the fool fails to understand what moral obligation consists in. In the remainder of the dissertation I turn my attention to two classical sentimentalist moral theories. I examine the theories of Hutcheson and Hume because it is not clear what resources moral sentimentalism has available to it in order to address questions about the reasonableness of moral action. In chapters 3 and 4, I develop an interpretation of Hutcheson who, because he distinguishes between exciting and justifying reasons, is able to say there is some non-derivative sense in which moral actions are reasonable. I argue that he develops a theory whereby moral obligation is to be understood in terms of the non-motivating states of approval of moral spectators, and I do not think, contrary to Darwall, that there is anything puzzling about his doing so. I argue that Hutcheson does not accept a version of motive internalism, but that he shares much in common with internalist views: he claims that there is a very strong, if contingent, connection between our states of approval and our motivational states. I offer an explanation of how Hutcheson could respond to the amoalist, which holds that we ought to be moral because, in part, we all already have the motives for and the interests in doing the sorts of things of which moral spectators approve. In chapters 5 and 6, I turn my attention to Hume who, because he makes no distinction between motivating and justifying reasons, does not seem to have anything to say about the non-derivative reasonableness of moral action. I argue that a textually grounded interpretation of Hume's theory of the passions provides us with more reason to favor an internalist reading over an externalist reading of his moral theory. Much of my argument depends on an interpretation of Hume's claim that it is possible for agents to be moved to act from a sense of duty alone. When we ask what Hume can say to the question “why be moral,” some of the options that Hutcheson pursues are initially open to him. However, I argue that Hume thinks philosophical theorizing must give way to the operations of psychological mechanisms that are causally responsible for inspiring agents to act morally by giving rise in them to particular kinds of affections. I conclude with some general remarks about the problems surrounding Darwall's interpretation of Hume's theory of justice, and use this discussion to lend further support to the claim that the actual theories of Hobbes, Hutcheson, and Hume do not neatly fit into the taxonomies that Darwall seems to think they do. (shrink)