This paper examines the factors conditioning the production of linguistic variables in real time by individual speakers: what we term the dynamics of variation in individuals. We propose a framework that recognizes three types of factors conditioning variation: sociostylistic, internal linguistic, and psychophysiological. We develop two main points against this background. The first is that sequences of variants produced by individuals display systematic patterns that can be understood in terms of sociostylistic conditioning and psychophysiological conditioning. The second is that psychophysiological conditioning and internal linguistic conditioning are distinct in their mental implementations; this claim has implications for understanding the locality of the factors conditioning alternations, the universality and language-specificity of variation, and the general question of whether grammar and language use are distinct. Questions about the dynamics of variation in individuals are set against community-centered perspectives to argue that findings in the two domains, though differing in explanatory focus, can ultimately be mutually informative.