According to "Foundations of Psychology" (1948), "psychology is the study of human nature. It is the study of man, man as a living being, acting in an ever-changing world, responding to things and events and other people. If you know what man is, if you know the full answer to the question about the nature of man, then you know what human nature is and what psychology comprises" (Chapter 1, Para. 1). Many varying thoughts have changed over time to the study of psychology. These thoughts include functionalism, behaviorism, structuralism, psychoanalysis, and humanistic.