John Kelly, the 50th anniversary of whose commencement of the new series of the Irish Jurist is celebrated in these pages, reached a memorable verdict on contemporary legal philosophy. In a comment alluded to by both Tony Honord and Ronan Keane in their respective forewords to his posthumously published monograph, A BrieffHistory of Western Legal Theory, Kelly describes today's students as being treated to a "course in mental ... athletics, sweating around the cinder-track of mid-twentieth-century linguistic analysis...".' On the question of the nature of law, Kelly's verdict is half right. This essay considers first what it gets wrong, and then what it gets right. The contributions to legal philosophy of H.L.A. Hart and Ronald Dworkin were the principal targets of Kelly's disapproval. There is no question that, following their example, contemporary legal theorists have sought to apply insights from other philosophical fields. We may justifiably speak of legal philosophy's interdisciplinary turn. But both Hart and Dworkin's initial efforts effected indispensable advances. Conversely, whereas subsequent interdisciplinarity has introduced much technical sophistication, it has yet to produce a corresponding payoff in understanding. Moreover, it is to legalphilosophy that the insight of the other domain is almost always applied. In the hands of sparring legal philosophers, interdisciplinarity can take on the appearance of an arms race; in the hands of philosophers from these other disciplines, it can take on that of show-stopping, but, ultimately, mark-missing, intervention. This suggests an organising theme of legal philosophy as patient. For all the benefits of the interdisciplinary turn, realised and potential, legal philosophy will remain an immature inquiry until it contributes reciprocally to cognate fields. Part I reviews the great advance achieved by Hart and Dworkin through the application of insights from the philosophy of language. Part II reviews the subsequent technical expansion of legal philosophy in the service of theories that both distinguish and fuse law and politics. In a concluding section, I consider the prospects for the converse scenario, in which legal philosophy exerts influence on another domain, namely, the philosophy of group agency.