There are three mental structures that explain this theory, the id, ego, and superego. The id is biological instincts and urges, and operates on pleasure. Ego, or "executive" relates desires from id to external realities. Ego is reality based and uses thinking, planning, problem solving and deciding. It also has a conscious control of personality. Superego judges or censors the actions of ego, this is what we know as our conscience. Humanistic theories focus on experience, problems, potentials and ideas, or what can be improved. It views human nature as inherently good, and not just moldable responses. Humanists believe that a person is a product of all the choices he or she has made. Behaviorist theories looks at personality in a more scientific way, explaining that personality is learned through classical and operant conditioning, observational learning, reinforcement, extinction, generalization and discrimination. This theory also stresses external causes of a person's actions, or how something is perceived and