Psychology \Psy*chol"o*gy\, n. pl. {Psychologies}. [Psycho- + -logy: cf. F. psychologie. See {Psychical}.] The science of the human soul; specifically, the systematic or scientific knowledge of the powers and functions of the human soul, so far as they are known by consciousness; a treatise on the human soul. Psychology, the science conversant about the phenomena of the mind, or conscious subject, or self. --Sir W. Hamilton.