The connection between idealizations, competence and multi-level explanations in cognitive psychology is discussed, in response to Patterson's ([1998]) reply to Franks ([1995]). I argue that idealizations are inherent in competence explanations and as a result, such explanations cannot be formulated in the multi-level terms widely used in the cognitive sciences. Patterson's argument was that neither competence nor performance involve idealizations, and, since they are separate 'systems', it is inappropriate to apply a single multi-level explanation to them. I suggest that there (...) is evidence that, although competence and performance are very often explicated in terms of levels of description, both none the less involve idealizations. However, I also suggest that Patterson's argument rests on confounding the demarcation of cognitive explanations with the demarcation of cognitive systems. Hence, even if competence and performance are different levels of a single system, questions concerning idealizations still arise when they are combined in an explanation. (shrink)