Psychology is defined as the scientific study of behavior and mental processes, encompassing everything from brain function and perception to social interactions and psychological disorders. Its formal beginning is usually dated to 1879, when Wilhelm Wundt established the first psychology laboratory in Leipzig, Germany; for this reason, Wundt is widely regarded as the father of modern psychology. Shortly afterward, the discipline began branching into distinct schools of thought, each proposing a different way of understanding the mind.
Edward Titchener founded structuralism, the earliest school, which attempted to break conscious experience into its basic elements through introspection, a process of looking inward to examine one's own thoughts and feelings. In contrast, William James championed functionalism, emphasizing how and why mental processes help organisms adapt to their environment. James's influential 1890 textbook "The Principles of Psychology" covered habit, emotion, consciousness, and the self. John B. Watson then proposed behaviorism, arguing that psychology should focus exclusively on observable, measurable behavior and ignore internal mental states. Sigmund Freud took a very different direction by founding psychoanalysis, a theory and therapy that emphasizes unconscious desires, conflicts, and childhood experiences. Later, Carl Rogers and Abraham Maslow developed humanistic psychology, which emphasizes free will, personal growth, and the drive toward self-actualization, viewing people as inherently good and striving for their full potential.
By the 1950s and 1960s, the cognitive revolution shifted psychology back toward studying internal mental processes such as thinking, memory, and problem-solving, partly as a reaction against behaviorism's narrow focus. Today, most psychologists adopt an eclectic perspective. The biopsychosocial model, for instance, explains behavior and mental processes as products of biological factors (such as genetics and brain chemistry), psychological factors (such as thoughts and emotions), and social factors (such as culture and relationships), all interacting together. This integrative view also frames the classic nature versus nurture debate, the longstanding question of whether behavior is shaped primarily by genetics and biology or by environment and experience. Modern psychology recognizes that both sets of factors interact continuously throughout life.