According to the American Psychological Association, "psychology is the study of the mind and behavior. The discipline embraces all aspects of the human experience—from the functions of the brain to the actions of nations, from child development to care for the aged." Psychologists use psychotherapy to treat patients by attempting to alleviate symptoms through bringing about changes in thought and behavior.
The word psychology comes from the Greek words psyche, meaning "breath," "spirit," or "soul," and logia, which indicates the "study of."
There are several branches of psychology. For example, clinical psychology has to do with treatment of mental health disorders. Cognitive psychology looks at the mental processes that affect behavior such as memory, attention, perception, learning, and so on. Developmental psychology has to do with the emotional, social, cognitive, and physical changes that people experience throughout their entire lives. Forensics psychology applies psychological principles to the law and criminal investigations. Neuropsychology looks at psychological processes in relation to brain structure and function.
Other branches of psychology include occupational psychology, social psychology, military psychology, health psychology, and evolutionary psychology. Because psychology is concerned with the human mind and behavior, it is a dynamic field, and new branches open up according to contemporary needs. For instance, psychologists are now studying traffic psychology, aviation psychology, and online psychology.
Taken as a whole, "Psychology is the Science of Mental Life, both of its phenomena and of their conditions. The phenomena are such things as we call feelings, desires, cognitions, reasonings, decisions, and the like," per William James, one of the founders of the field. Indeed, given James's definition, the study of psychology is as diverse as the mind is complex.