How can we integrate interrelated theories of individual elements of cognition? Computational models of reasoning processes encode an understanding of reasoning. Consequently, a computational modeling language may be ideally suited to the presentation of theories of cognition. By representing theories of a variety of phenomena in a single modeling language, we can potentially explore how these theories might interact. The Task-Method-Knowledge (TMK) modeling language evolves from artificial intelligence research on the subject of multistrategy reasoning. TMK models provide a compositional account of reasoning processes; they describe not only what the elements of a process are, but also how the functional properties of these elements combine to form the functional properties of the process as a whole. This paper explores the composition of theories of cognition within the TMK framework, drawing on some existing theories within cognitive science as examples.