The study of human nature may be thought of as an art with many tools at its disposal, an art closely related to all the other arts, and relevant to them all. In literature and poetry, particularly, this is especially significant. Its primary aim must be to broaden our knowledge of human beings, that is to say, it must enable us all to become better, fuller, and finer people.
I was listening to a cognitive psychologist lecture, and he explained some phenomena or other and asked "What might be the reason for this?" I don't remember what 'this' was, but I do recall thinking, "Maybe it's a psychological reason," and then doing a quick mental double take. Clearly he and I were looking at psychology from different angles. For me his course could have been titled 'The Rise and Fall of Theories in Biopsychomechanics.'
The saving grace of the course was the energy, enthusiasm, and personality of himself and the TA. Yet those terms themselves seemed to be outside the province of the course.
Psychology should have something to do with 'the psyche', should it not? Unfortunately it is very difficult to define and study 'psyche' experimentally. Behaviorists solve the problem by limiting study to observable behaviours, yet with both behaviorism and cognitive psychology one feels that a great deal gets lost in the process.
A classic definition used to be 'Psychology is concerned with understanding, predicting, and controlling human behaviour.' That holds true today, but different fields have differing emphases on (and definitions for) 'understanding', 'predicting', and 'controlling', as well as differing in what they're prepared to include in their understanding of 'behaviour'. While there are differences between various theoretical approaches and paradigms in psychology, the Art embraces them all, even the most diametrically opposed.