Individuals' use of language in contexts emerges from second-to-second processes of activating and integrating traces of past experiences--an interactionist view compatible with the study of language as a complex adaptive system but quite different from the trait-based framework through which measurement specialists investigate validity, establish reliability, and ensure fairness of assessments. This article discusses assessment arguments from an interactionist perspective. We argue that the familiar concepts and methods of assessment that evolved under a trait perspective can be gainfully reconceived in terms of the finer-grained perspective of interactionism, and we illustrate how key ideas relate to familiar practices in language testing.