This activity relates to differentiation, a concept Bowen called a cornerstone in his theory (1978). Differentiation of self describes the degree to which a person is able to distinguish between intellectual and emotional processes. In other words, differentiation is how well a person can separate thinking and feeling, and avoid being controlled by his or her emotions. A welldifferentiated person is able to filter his or her emotions through his or her intellectual thoughts and respond accordingly. Differentiated people are not cold and distant, but instead are able to be emotionally involved with others in a thoughtful manner (Bowen, 1978), The more differentiated a person is, the less reactive he or she will be in relationships. Reactivity is a term for how much a person's behavior is fueled by his or her emotions in interactions with others. An undifferentiated person is likely to be reactive and respond with strong emotions without thinking through the results of his or her response. Reactivity triggers reactive responses from others resulting in a pattern of established behavior in the family (Papero, 1990). Bowen referred to this reactivity in families as emotional fusion.