Normative Principles are Synthetic A Priori

I argue for the claim that there are instances of a priori justified belief – in particular, justified belief in moral principles – that are not analytic, i.e., that cannot be explained solely by the understanding we have of their propositions. §1–2 provides the background necessary for understanding this claim: in particular, it distinguishes between two ways a proposition can be analytic, Basis and Constitutive, and provides the general form of a moral principle. §§3–5 consider whether Hume's Law, properly interpreted, can be established by Moore's Open Question Argument, and concludes that it cannot: while Moore's argument – appropriately modified – is effective against the idea that moral judgments are either (i) reductively analyzable or (ii) Constitutive-analytic, a different argument is needed to show that they are not (iii) Basis-analytic. Such an argument is supplied in §6. §§7–8 conclude by considering how these considerations bear on recent discussions of “alternative normative concepts”, on the epistemology of intuitions, and on the differences between disagreement in moral domains and in other a priori domains such as logic and mathematics.