Many basic problems and disagreements in cognitive science are due to unresolved yet fundamental conceptual muddles. It is difficult to progress beyond this state unless we work towards the definition of a coherent set of basic terms that can be consistently used by all cognitive scientists. In this commentary, we provide a set of definitions of concepts that are regularly used in systems theory. We then use these concepts to illustrate some of the difficulties that Green points to, and to derive some claims regarding the plausibility of AI as the methodological cornerstone of cognitive science.