This paper examines the interplay between conceptual structure and the evolution of scientific concepts, arguing that concepts are fundamentally ‘forward-looking’ constructs. Drawing on empirical studies of similarity and categorization, I explicate the way in which the conceptual taxonomy highlights the ‘relevant respects’ for similarity judgments involved in categorization. I then propose that this taxonomy provides some of the cognitive underpinnings of the ongoing development of scientific concepts. I use the concept synapse to illustrate my proposal, showing how conceptual taxonomy both facilitates and constrains the accommodation of newly discovered phenomena. I end by briefly considering the implications of the proposed approach for a normative evaluation of scientific concepts.