Broad concern for language issues in evaluation has been limited in comparison to other social science disciplines. In this article, some occasions of definitional or conceptual confusion with evaluation theory language are identified that emerged during a study conducted by Christie. We suggest that much of the language we use to describe evaluation practice is steeped in theoretical terminology, which may limit the utility of the language. We also argue that theoretical language ought to be used with great care, with attention to the subtleties and nuances of terms, for there may be unexpected confusion or ambiguity in the field about the terms we routinely use. A research agenda is offered, suggesting that it would be both an informative as well as a useful task for us to learn more about the everyday "folk theories" of the field and the vernacular used to describe them.