Theories of the cognitive architecture (Langley et al., 2009) aim to specify the constant features of the human mind. They make assumptions about the representation and organization of memory, as well as about performance and learning mechanisms that operate over these structures. They specifically do not include content that changes, whether rapidly through reasoning and problem solving or gradually through learning. However, we also know that humans are highly adaptive and that they can work on the same task in many different ways. This creates a tension between the desire to identify universals in human cognition and to explain the observed variation. Some architectures, like Soar and Epic, make few commitments except about knowledge representation and the basic cognitive cycle. In contrast, Icarus (Langley et al., 2009), makes more specific claims about the mechanisms that underlie behavior.