Freud believed that abnormal behavior and personality could be explained by unconscious motives and drives. He used techniques like hypnosis and free association to explore the unconscious mind. However, psychoanalysis has been criticized for its lack of scientific rigor and validation of techniques like dream interpretation. Abraham Maslow introduced humanistic psychology, which viewed people as having free will and an innate drive for self-actualization, rather than being governed by unconscious forces or external stimuli. Modern psychology incorporates multiple perspectives including biological, psychodynamic, humanistic, cognitive, social, behavioral, and developmental approaches to understand and explain human behavior.