Engraved above the entrance to the temple of Apollo at Delphi was the maxim “Know thyself.” Ever since Socrates and Plato speculated on the nature of the human mind, serious thinkers have sought to understand the self and human behavior. Today, scientists are attempting to translate abstract philosophical and psychological questions about mind into the empirical language of cognitive psychology and brain biology.
— Eric Kandel, In Search of Memory

Psychology: the study of mental and behavioral processes. (Kleinman, 7) The science of human nature. The study of sensitivity, action, and consciousness. (Pyle, 4)

Examines mental processes … manifested in our thoughts, speech, and behavior. From the Greek words psych, meaning ‘soul’ or ‘mind,’ and logia, a ‘study’ or ‘account.’ Psychologists themselves are unlikely to agree on a single definition of the word. (Collin, 10) The definition offered by any particular psychologist reflects their own interpretative “bias,” therefore some would lay more stress on the ‘mind’ part of this definition, others the ‘behavior’ part. Some psychologists might even offer the view that the study of human behavior cannot, and indeed should not, be considered a scientific discipline. (Cardwell, 195)