The cornerstone of Bowen Theory, the first of his eight theoretical concepts, was what he called differentiation—the measure of a person’s or family’s capacity to differentiate between their intellectual and emotional functions. In a nutshell, people who are highly differentiated are “resourceful people who engage difficult challenges with a view to solving problems and achieving goals” (Papero, 2018, p. 133). Such people have less anxiety and more capacity to bring their intellect to bear when emotions run high.

Bowen (1978) described the intrapersonal dimension of differentiation as one’s ability to be consciously aware of one’s thinking process while one is also engaged in one’s emotional process. The more highly differentiated person is able to access both thinking and feeling and is able to bring both to bear in times of tension and stress in order to make reasoned, principles choices.

The interpersonal dimension of differentiation refers to one’s ability to define oneself in relationship with others. The highly differentiated person, or the solid self, says:

‘This is who I am, what I believe, what I stand for, and what I will do or will not do,’ in a given situation. The solid self is made up of clearly defined beliefs, opinions, convictions, and life principles...incorporated into self from one's own life experiences, by a process of intellectual reasoning and the careful consideration of the alternatives involved in the choice. (Bowen, 1978, p. 365)

It is the reasoned, rather than the reactive self, that does not fuse, or become enmeshed with, others.