The primary goals of psychological science are to describe, explain, predict and influence behaviour and to apply psychological knowledge to enhance human welfare. Basic research is the quest for knowledge for its own sake, whereas applied research involves the application of knowledge derived from basic research to solve practical problems. Each perspective views human nature differently and focuses on different causes of behaviour. Psychology"s intellectual roots lie in philosophy biology, and medicine. Structuralism, which examined the basic components of consciousness, and functionalism, which focused on the purposes of consciousness, were psychology"s two earliest schools of thought. The psychodynamic perspective calls attention to unconscious motives, conflicts and defence mechanisms that influence personality and behaviour. Freud"s psychoanalytic theory emphasized unconscious sexual and aggressive impulses and early childhood experiences that shape personality. With roots in 18th-centruy british empiricism the behavioural perspective emphasizes how the external environment and learning shape behaviour.