Social psychologist Leon Festinger first proposed the theory in 1956: Cognitive dissonance is a psychological term which describes the uncomfortable tension that comes from holding two conflicting thoughts at the same time, or from engaging in behavior that conflicts with one's beliefs. More precisely, it is the perception of incompatibility between two cognitions, where "cognition" is defined as any element of knowledge, including attitude, emotion, belief, or behavior. The theory of cognitive dissonance states that contradicting cognitions serve as a driving force that compels the mind to acquire or invent new thoughts or beliefs, or to modify existing beliefs, so as to reduce the amount of dissonance (conflict) between cognitions. Experiments have attempted to quantify this hypothetical drive. Some of these examined how beliefs often change to match behavior when beliefs and behavior are in conflict.