Published online by Cambridge University Press: 01 January 2020
What role do the first principles of morals play in Reid's moral theory? Reid has an official line regarding their role, which identifies these principles as foundational propositions that evidentially ground other moral propositions. I claim that, by Reid's own lights, this line of thought is mistaken. There is, however, another line of thought in Reid, one which identifies the first principles of morals as constitutive of moral thought. I explore this interpretation, arguing that it is a fruitful way of understanding much of what Reid wants to say about the role of moral first principles and drawing some connections between it and recent work on moral nonnaturalism.