Defense mechanism
Splitting
People and feelings are sorted into all good or all bad.
Splitting keeps apart things that belong together. A person, a group, or one's own self is experienced as either wholly good or wholly bad, and the two pictures are not allowed to meet. The same friend can seem wonderful on Monday and impossible on Wednesday, with little sense of the other view in between.
It makes a complicated world simpler. Holding mixed feelings about someone who matters, love and anger at once, can be hard to bear, and splitting removes the need to: each feeling gets its own, separate object.
When his new manager praises his work, Daniel tells everyone she is the best boss he has ever had. A week later she asks him to redo a report, and he decides she has been against him from the start. Both times he is completely sure, and the earlier picture seems never to have existed.
When it helps
In small doses splitting brings clarity and the energy to act, which may be why it shows up in fairy tales and sports rivalries. Under heavy strain it can also hold a person together: if the bad is clearly over there, the good can be kept safe.
What it can cost
Relationships pay the most. People are rarely all good or all bad, so a view built on splitting has to swing, and those on the receiving end may find the swings confusing or hurtful. It also makes it harder to see one's own mixed qualities, and to forgive oneself or others.
How it differs
Idealization and devaluation are the two sides that splitting produces, seen one at a time: the overvalued person and the undervalued one. Projection moves a feeling onto someone else; splitting decides who is good and who is bad in the first place, and often prepares the ground for projection.
In McWilliams' model
McWilliams counts it among the primary defenses. These deal with the border between the self and the outside world, and they shape experience as a whole: what is felt, what is seen, and whose feeling is whose.
Character styles that lean on it
McWilliams treats splitting less as a mark of one character style than as a primary defense that anyone may fall back on under heavy strain, and that some people rely on much of the time. On this site it is closest to the idealizing and devaluing described for the narcissistic style.
Everyone uses defenses, every day, and noticing one in oneself does not mean that something is wrong. This page describes a general way of coping, not a diagnosis. If something described here is frequent, distressing, or gets in the way of daily life, it is worth discussing with a doctor or a mental health professional.