When therapists noticed that

What one spouse did provoked the other

Who then reprovoked the first, each in turn;

They began to realize that a dyad

Was unstable and that it required a third person

To prevent a runaway confrontation.

If a man and wife competed over who was sickest

And the therapist could only prevent a total collapse by becoming

Or otherwise involving a third party,

Rivalous quarrels that amplified in intensity

Required someone outside the dyad

To intervene and stabilize it.

The observation that a child

With a problem stabilizes a marital dyad

Led some therapists to the idea that the

Basic unit of family therapy should be

Parents and child.

In fact, one can note that the therapist

Replaces the child with the couple

And thus stabilizes the dyad.