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

the william james' model is the view on free will, though i'm not sure what the fourth self is.

the constituents of the self may be divided into two classes, those which make up respectively -

(a) the material self;
(b) the social self;
(c) the spiritual self; and
(d) the pure ego.

the question may be referring to the pure ego, but again i don't quite understand.