Moral rationalists have claimed a priori status for moral principles, including the commonsense principles described in Chapter 4. Intuitionists – prominently including Ross – have even claimed self-evidence for such principles. How can this claim be justified? Central to the case is the idea that normative properties are a priori grounded in certain non-normative natural properties. This chapter explains such grounding. In doing so, it distinguishes two kinds of normativity: a kind belonging to a priori grounds of obligation, e.g. promising – normativity in upshot – and another belonging to propositions, such as moral judgments, that employ normative concepts: this is normativity in content. The chapter shows how the commonsense principles control critical discourse in the constitutive ways appropriate to entrenched a priori generalizations. It also shows how their apriority squares with the empiricality of singular moral judgments and how, even where obligations conflict, singular judgments of overall obligation may be justified and known.