Cognition encompasses the mental functions by which knowledge is acquired, retained, and used: perception, learning, memory, and thinking. While some cognitive processes are carried out consciously and deliberately, others are carried out unconsciously and automatically. Moreover, it appears that implicit, unconscious expressions of perception, memory, learning, and thought can be dissociated from their explicit, conscious counterparts. Unconscious cognition appears to be a fact of mental life, although claims that unconscious cognition is more powerful than conscious cognition, that consciousness is not essential for cognition, or that conscious cognition is epiphenomenal in nature, go far beyond the facts.