My main purpose is to suggest that H. L. A. Hart's infamous "ascriptivism" 1 may be of considerable pertinence to the assessment of the nature of justificatory claims in the criminal law; in passing, I argue that ascriptivism gives no cause for infamy. My suggestion is developed in Part III: As it depends on some reformulation and endorsement of Hart's ideas, I discuss the "ascriptive" and "defeasible" character of the concept of action in Part II, and therein try to dismiss some of the severe criticism that ascriptivism has given rise to since its proposal. This criticism, I shall argue, often relies upon a poor or uncharitable interpretation of Hart's instrumental characterization of the "defeasibility" of legal concepts; for this reason, Part I is dedicated to a reconstructive elucidation of Hart's account of "conceptual defeasibility." 2