ABSTRACT
THEORETICIANS OF EQUILIBRIUM Contrary to a particularly widespread idea, Piaget is not the only psychologist whose theory is grounded on the notion of equilibrium. Indeed, if we define equilibrium in a very simple way as a principle that affirms a relation between a system (or an organism) and its environment, so that any change in the environment produces an adjustment of the system in the sense that it tends to keep constant a certain number of conditions of existence of the system which are considered desirable if not vital for the system in question, then the theories of Spencer (1892), Freud (1923-25/1964), Watson (1929), Dewey (1933), Heider (1946) and Festinger (1957) are theories based on the principle of equilibrium.
