While psychological knowledge is often applied to the assessment and treatment of mental health problems, it is also directed towards understanding and solving problems in several spheres of human activity.
By many accounts psychology ultimately aims to benefit society.
However, this meaning was contested, notably by radical behaviorists such as John Watson, who in his 1913 manifesto defined the discipline of psychology as the acquisition of information useful to the control of behavior.
Psychologists of diverse orientations also consider the unconscious mind.
Psychologists employ empirical methods to infer causal and correlational relationships between psychosocial variables.
The ancient civilizations of Egypt, Greece, China, India, and Persia all engaged in the philosophical study of psychology.
Historians note that Greek philosophers, including Thales, Plato, and Aristotle (especially in his De Anima treatise), In China, psychological understanding grew from the philosophical works of Laozi and Confucius, and later from the doctrines of Buddhism.
In Germany, Gottfried Wilhelm Leibniz (1646–1716) applied his principles of calculus to the mind, arguing that mental activity took place on an indivisible continuum—most notably, that among an infinity of human perceptions and desires, the difference between conscious and unconscious awareness is only a matter of degree.
Christian Wolff identified psychology as its own science, writing Psychologia empirica in 1732 and Psychologia rationalis in 1734.In this field, a professional practitioner or researcher is called a psychologist and can be classified as a social, behavioral, or cognitive scientist.Psychologists attempt to understand the role of mental functions in individual and social behavior, while also exploring the physiological and biological processes that underlie cognitive functions and behaviors.This body of knowledge involves insights drawn from introspection and observation, as well as techniques for focused thinking and acting.It frames the universe as a division of, and interaction between, physical reality and mental reality, with an emphasis on purifying the mind in order to increase virtue and power.Yoga is a range of techniques used in pursuit of this goal.