Various recurring themes in the history of the subject are reviewed. In the context of adaptation to a complex environment, one precondition for survival must be a capacity for object identity, which may be the most basic form of categorization. Evidence will be presented that suggests that the capacity is not learned. In considering learned associations among categorized items, a distinction is made between reflexive and reflective processes: that is between those associations in which a cue or signal provides an unambiguous route to the response, no matter how complex that route may be, in contrast to those in which learned information must be ordered and reordered `in thought'. An example of one experimental approach too the latter is provided. Finally, the problem of conscious awareness is considered in terms of stored categorical knowledge and associations, on the hand, and a system that monitors them, on the other. Neurological evidence of disconnections between these different levels is reviewed.