In this article two theories of human cognition will be discussed, those of Anderson (1983) and Tulving (1983). It is claimed that in these theories category mistakes can be discerned, because of the fact that various levels of description and also various forms of representation are confused. The instruments for analyzing the levels of description and forms of representations have been borrowed from Dennett (1978) and Arnheim (1971). It is stated that in order to study mental representations the different features of mental codes (or symbols) should be investigated.