The basis of coherence therapy is the principle of symptom coherence. This is the view that any response of the brain–mind–body system is an expression of coherent personal constructs (or schemas), which are nonverbal, emotional, perceptual and somatic knowings, not verbal-cognitive propositions. A therapy client's presenting symptoms are understood as an activation and enactment of specific constructs. The principle of symptom coherence can be found in varying degrees, explicitly or implicitly, in the writings of a number of historical psychotherapy theorists, including Sigmund Freud (1923), Harry Stack Sullivan (1948), Carl Jung (1964), R. D. Laing (1967), Gregory Bateson (1972), Virginia Satir (1972), Paul Watzlawick (1974), Eugene Gendlin (1982), Vittorio Guidano & Giovanni Liotti (1983), Les Greenberg (1993), Bessel van der Kolk (1994), Robert Kegan & Lisa Lahey (2001), Sue Johnson (2004), and others.