How psychologists define the concepts that they will investigate influences not just the conclusions that they draw but the very forms of experimentation that they use. Indeed, empirical analysis typically presupposes some (at least implicit) conceptual work. This conceptual work can and characteristically does draw on intellectual traditions of a philosophical or theological variety. These traditions provide not just rival definitions but also other insights that can be useful for psychological investigations. My remarks in this essay focus not just on definitional issues but also on some aspects of the philosophical or theological tradition that may be of interest to researchers in positive psychology.