1Psycho-analytic psychology deals with the manifestations in behaviour and in subjective perception of motivations of the biological organism as a unit. Such motivations, or some of them, are commonly called 'drives', 'instincts' or instinctual forces.

2They are properly termed 'forces' because they activate the physical behaviour of the organism and because they arise from the chemistry and physiology of the protoplasm, acting through cells and organs of which the human organism is constituted. In other words, the subject matter of psycho-analytic psychology, the fantasies and motivations which underlie feeling, thinking and behaviour, are subjectively perceived as reflections in the mind of the chemistry and physiology of the body. Sex urges and the fight-flight reactions are examples.