Starting with distinction between explicit and implicit knowledge and the traditional philosophical distinction between COS (the consciousness of self) as an object and COS as a subject, we suggest a triple classification of COS experience into three modes, each corresponding to a different state of consciousness. When one acts automatically COS is totally embedded within the representation of the environment. When one monitors or attends to one's experience, the self is implied by an explicit representation of one's attitudes, consistent with Descartes' cogito insight 'I think therefore I am' (1641,1984). However, a reflexive thought, e.g., 'I know fact x,' requires an explicit representation of the self. This analysis highlights the existence of an intermediate mode of COS as a subject and suggests its possible connection to monitoring one's behavior.