Lewin's equation

Lewin's equation, B=ƒ(P,E), is not actually a mathematical equation representing quantifiable relationships but rather a heuristic designed by psychologist Kurt Lewin. It states that behavior is a function of the person and his or her environment.

$$B=f(P.E)$$

The equation is the psychologist's most well known formula in social psychology, of which Lewin was a modern pioneer. When first presented in Lewin's book Principles of Topological Psychology, published in 1936, it contradicted most popular theories in that it gave importance to a person's momentary situation in understanding his or her behavior, rather than relying entirely on the past.