Gaining a perspective on the evolution of psychological concepts can show students the power of theory and societal perspective in shaping scientific ideas across time. In this article, the author uses two constructs, the broad concept of intelligence and the narrow concept of combat stress reaction, to illustrate how psychologists have grappled with these ideas over the past century. These examples can provide a model for using the history of psychology to explain how ideas have taken their shape. These illustrations also show the difficulty in developing ideas that are scientifically useful and that periodic changes in the conceptualization of ideas are a normal feature of a dynamic discipline. (Contains 1 figure.)