Self - S. Kierkegaard.

The human being is spirit. But what is spirit? Spirit is the self. But what is the self? The self is a relation which relates to itself, or that in the relation which is its relating to itself. The self is not the relation but the relation's relating to itself. A human being is a synthesis of the infinite and the finite, of the temporal and eternal, of freedom and necessity. In short a synthesis. A synthesis is a relation between two terms. Looked at in this way a human being is not yet a self. 

A. That Despair is the Sickness unto Death - The Sickness unto Death

Soren Kierkegaard