Modern researchers have not yet determined what causes
depression, but the mood disorder appears to be related to
elevated stress and life changes, and may be influenced by brain
chemicals. Although the precise cause of depression is unknown,
there are a number of theories that attempt to explain how it
occurs. Proponents of psychoanalytic theory generally maintain
that depression is the result of an unconscious problem, and
that depressed people turn their anger and hostility inwards in
order to avoid conflict with the outside world. Learning
theorists suggest that depression is the result of learning to
be helpless. That is, when people come to believe they have no
control over their lives, socially, economically, or
psychologically, they tend to give up trying and depression sets
in. Psychologists who favor cognitive theories generally argue
that when a person experiences self-defeating thoughts or dwells
on negative thoughts for too long, low self-esteem and
depression occur as a result. Biological theori