It is a serious problem for some well-known accounts of moral motivation, that is, accounts of what ought to motivate us, that what is supposed to provide motivation to act well instead provides motivation to self-deceive. I term this the Self-Deception Problem. Any theorist who offers an account of moral motivation that has the Self-Deception Problem has reason for concern with our tendency to self-deceive. In this dissertation, I create a taxonomy of accounts of moral motivation, which provides a structural explanation for which accounts of moral motivation are liable to the Self-Deception Problem. Using this taxonomy, I am able explain why Thomas Reid, Adam Smith, and Joseph Butler are concerned with self-deception as a moral problem in a way that Thomas Hobbes, John Locke, and Francis Hutcheson are not. But the application of my taxonomy is not limited to the seventeenth and eighteenth centuries. I also show how it fits the work of the contemporary psychologist Augusto Blasi and the contemporary philosopher Christine Korsgaard. Neither Blasi nor Korsgaard discusses self-deception in any thoroughgoing way but, as I argue, since both their accounts have the Self-Deception Problem, both of them have reason to do so. The most interesting theorist of moral motivation and self-deception, though, is Joseph Butler. Through a close reading of his arguments for the authority of conscience, I show how his account gives rise to the Self-Deception Problem, and how his sermons on self-deception serve as explanations of and responses to that problem. But the link is even tighter than that: on my novel interpretation of Butler's arguments in favor of the authority of conscience, what he is in fact arguing for is an appropriate degree of self-trust. His discussion of self-deception can accordingly be understood as seeking a proper degree of self-suspicion. On Butler's view, moral agency is not just a matter of recognizing our divinely set proper ends. Nor is it just a matter of acting as a self-legislating agent. It is primarily a matter of correctly modulating self-trust and self-suspicion.

Joseph Butler's moral thought and the ethical rationalism of Samuel Clarke, and his followers, John Balguy and Richard Price, are frequently distinguished, as a result of: (a) Butler’s empirical method (e.g., Kydd, Sturgeon); (b) Butler's emphasis upon self-love in the 'cool hour passage' (e.g., Prichard, McPherson); (c) Butlerian conscience, where, on a neo-Kantian reading, Butler surpassed the Clarkeans by conveying a sense of Kantian 'reflective endorsement' (e.g., Korsgaard, Darwall). The neo-Kantian criticisms of the Clarkeans in (c) are consistent with (d) Francis Hutcheson's and David Hume's criticisms of the Clarkeans; (e) modern criticisms of rational intuitionism that follow Hutcheson and Hume (e.g., Mackie, Warnock); and (f) the contention that the Clarkeans occupied an uneasy position within 'post-restoration natural law theory' (e.g., Beiser, Finnis). (d)-(e) thus underpin the distinction between Butler and the Clarkeans in (a)-(c), where the Clarkeans, unlike Butler, are criticised for representing moral truth as the passive, and self-evident, perception of potentially uninteresting facts. This study responds to (a)-(f), by arguing that Butlerian and Clarkean conscience possessed more than one referent; so that conscience meant an individual's experience of his own judgement and God’s judgement and the rational moral order. As a result of their shared theory of conscience, Butler and the Clarkeans held the same theory of moral development: moral agents mature as they move from obeying conscience according to only one of conscience's referents, to obeying conscience because to do so is to satisfy each of conscience's referents. In response to (a)-(b), this study demonstrates that the Clarkeans agreed with Butler’s method and 'cool hour': natural considerations of individual judgement and self-interest were necessary aspects of the progress towards moral maturity in both Butler and the Clarkeans. With respect to (c), it is argued that Butler and the Clarkeans shared the same understanding of practical moral reasoning as part of their shared understanding of conscience and moral development. This study places limits upon proto-Kantian readings of Butler, and neo-Kantian criticisms of the Clarkeans, while making it inconsistent to divide Butler and the Clarkeans on the basis of Butlerian conscience. In answer to (c)-(f), Clarkean conscience shows that the Clarkeans were neither complacent nor ‘externalists’. Clarkean conscience highlights how the Clarkeans positioned themselves within the tradition of Ciceronian right reason and Thomistic natural law. Consequently, in both Butler and the Clarkeans, the intuition of moral truth was not the passive perception of an 'independent realm' of normative fact, but the active encounter, in conscience, with reason qua the law of God’s nature, human nature, and the created universe.