An influential strand in recent action-theory employs constitutivist arguments in order to present accounts of individual agency and practical identity. I argue for an extension of this framework into the interpersonal realm, and suggest using it to reassess issues in jurisprudence. A legal system is an instantiation of the solution to the inescapable tasks of self-constituting action and identity-formation in the presence of other agents. Law's validity and normativity can be enlightened when the constitutivist approach considers the external prerequisites of (...) individuals' self-conceptions qua agents. More specifically, this argumentative strategy allows a reassessment of Fuller's “internal morality of law.” Whereas, pace Fuller, morally substantive conclusions cannot be derived from formal criteria of legality, there are unconditional normative requirements that constrain law. (shrink)