As a biological science, it studies the physiological mechanisms and evolutionary origins of mental and behavioural phenomena. As a social science, it studies personality and interpersonal relations and their bases in social interaction, cognition and emotion. As a cognitive science, it studies such processes as sensation and perception, abstract thinking, reasoning, language, and memory. Developmental psychology combines all three aspects in taking for its subject matter the total life span. The objectives of psychological study are to understand human nature, for its own sake, and to provide an increasingly reliable basis for the application of psychological principles to education, social policy, and medical treatment.
Psychologists use a variety of methods appropriate to the questions they study.
Experimentation, laboratory techniques, observational procedures, measurement, and statistical methods are among the important tools of the psychologist. Whatever their methods, psychologists share in their research a commitment to careful and systematic observation aimed at the formulation of general principles. In recent years psychology has become increasingly interdisciplinary. Psychologists work with biologists, geneticists, medical researchers, physiologists, and biochemists on those questions of a biological nature. They work with sociologists, criminologists, anthropologists, and economists, among others, on questions relating to social behaviour.