There can be reasons for belief, for action, and for feeling. In each case, knowledge of such reasons requires non-empirical knowledge of some truths about them: these will be truths about what there is reason to believe, to feel, or to do – either outright or on condition of certain facts obtaining. Call these a priori truths about reasons, ‘norms’. Norms are a priori true propositions about reasons.

It's an epistemic norm that if something's a good explanation that's a reason to believe it. It's an evaluative norm that if someone's cheated you that's a reason to be annoyed with them. There are many evaluative norms, relating to a variety of feelings. Equally, there may be various epistemic norms, even though in this case they all relate to belief. My concern here, however, is with practical norms: a priori truths about what there is reason to do.

I have a suggestion about what fundamental practical norms there are, which I would like to describe and explain. It is that there are just three distinct kinds of practical norm governing what there is reason to do – three categories or generic sources of practical normativity, one may say. I call them the Bridge principle, the principle of Good, and the Demand principle – Bridge, Good and Demand for short. I have said more about them in my book, The Domain of Reasons;1 here my aim is simply to set them out and sketch some questions to which this ‘triplism of practical reason’2 gives rise. In particular, since these norms are about practical reasons, not about morality, a question I'll touch on is how moral obligation comes onto the scene.