The cognitive systems literature describes many methods for problem solving and planning. Given a goal state, these methods search for solutions that achieve the goal through interactions with some environment. However, a major assumption is that goals are given, usually by a user directly as input or as part of the problem representation. Furthermore, once given, the goals do not change. Here, we formalize the notion that goal formulation and goal change are themselves major cognitive operations. We include in our model not just plan generation and execution but also interpretation of the environment as plans execute, exogenous events occur, and plans change.