Differentiation and fusion is how Bowen describes the extent to which people can separate their emotional and intellectual spheres

Differentiation and fusion is how Bowen describes the extent to which people can separate their emotional and intellectual spheres (Rabstejnek, n.d.). People with higher levels of differentiation have less emotional reactivity, with an ability to calm their emotions and make more thoughtful and intentional decisions. Having a higher level of independence, more tolerance to stress, they are less prone to triangulation. Along with an ability to remove themselves from emotional entanglements, they can have a closeness without getting lost in the relationship. Generally, relationships are fulfilling.
On the other hand, fusion, or lack of differentiation as described by Brown (1999), is where the individual chooses family harmony over themselves. Such people are more emotively reactive, having difficulty in managing thoughtful behavior. They have difficulty saying no to people, tending to be critical and judgmental, and are overly concerned about approval from others. Dependent on others, difficulty in communicating and making decisions, they are prone to triangulation. Problematic relationships end to be repeated rather than learning from their mistakes.