L. J. Henderson was a central figure in Harvard discussions of the nature of science in the interwar period and served as a bridge between the sciences and the social sciences. Two key ideas were promoted by Henderson: systems and conceptual schemes, both of which spread quickly at Harvard and then beyond. In this article the focus will be on conceptual schemes, a term which had a distinctive origin in Henderson that accounts for some of the ambiguities in its adaptations. (...) Henderson spoke as a scientist speaking to philosophers rather than doing philosophy and sharply distinguished his aims from those that followed from Immanuel Kant. Henderson’s model was the scheme of ancient Greek medicine, which had persisted for millennia and was replaced by modern medicine. This was differentiated from earlier neo-Kantian and later Kuhnian variations. Henderson’s account was distinctive in placing the origins of conceptual schemes in intuitions about patterns formed in practice by people operating on concrete phenomena. The resulting schemes, he thought, had to be accepted on faith by students, but were, as he put it, walking sticks to enable communication and understanding rather than exclusive dogmas. Henderson was an enthusiast for Vilfredo Pareto, who was vilified at Harvard during the war by Carl J. Friedrich, which led not to the disuse of his ideas but to the erasure of their origins. (shrink)