If you were to add a “fourth self” to william james’ model, what would it be? why?

The pure ego could be the fourth self. The self can be divided into two classes which are indeterminism and compatibilism

The correct answer to this open question is the following.

The “fourth self” to William James’ model, would be the "pure Ego."

William James (1842-1910) was a US psychologist who was the first one to teach a psychology course in America. He also developed the theory of the Self, stating that there is a "Me self" and an "I self." For him, the elements of the self were the material self, the social self, the spiritual self, and the fourth component should be the pure Ego self.

accelerated heartbeat, raise in blood pressure, slow in digestion, raise in blood sugar and perspiration. (myers' psychology for ap 2nd edition pg 87)