Descartes argued that the ultimate truth can be deduced only from the real existence of a "thinking self." He assumed that the "thinking self" is independent of body or matter, as it does have an extension we can see and touch but does not think, a mind has no extension but thinks.

The early views of mind had the Greek philosophers identifying three aspects of the mind: Cognition (acts of intellect), conation (acts of will), and affect (acts of emotions) These are related to what we today identify as the distinction between structure (organization) and process (action).