1. in philosophy, the doctrine that pleasure is an intrinsic good and the proper goal of all human action. One of the fundamental questions of ethics has been whether pleasure can or should be equated with the good in this way.

2. in psychology, any theory that suggests that pleasure and the avoidance of pain are the only or the major motivating forces in human behavior. Hedonism is a foundational principle in psychoanalysis, in behaviorism, and even in theories that stress self-actualization and need fulfillment. To the extent that human beings are hedonistic, it is difficult to admit the possibility of genuine altruism. Also called hedonistic psychology. See eudemonism; hedonic psychology. —hedonistic adj.