Abstract

This dissertation is a critical study of rationalism in ethics: the view that acting morally is a requirement of rationality, and that all agents consequently have reason to be moral. The study attempts first to reconstruct the essential elements of the rationalist approach in ethics, and then to identify the most critical obstacles in the way of that approach. By way of reconstruction, it is argued that the rationalist in ethics needs to construe rationality as a set of ideal principles or norms, and to affirm a connection between one's having a practical reason and the capacity of rationality to lead one to be motivated to act on the reason. This latter claim amounts to a version of internalism, and some time is devoted to the task--hitherto neglected by philosophers--of clarifying and defending the connection which it postulates between practical reasons and the motivation to act on them. Given internalism, the burden on the rationalist is to show that rational reflection can by itself lead to the motivation to act on moral reasons. Opponents of rationalism have characteristically challenged the very possibility of such purely rational motivations, and the dissertation considers next the arguments that have been offered for this broadly Humean position. The conclusion is reached that there are no plausible a priori arguments against the very possibility of a rationalist explanation of motivation. This does not however represent a vindication of the rationalist approach: there is room for a pragmatic argument against purely rational explanations of motivation, and the dissertation concludes by offering such an argument, focussing in particular on the case of prudence and prudential reasons.