The projection outwards of internal perceptions is a primitive mechanism, to which, for instance, our sense perceptions are subject, and which therefore normally plays a very large part in determining the form taken by our external world. Under conditions whose nature has not yet been sufficiently established, internal perceptions of emotional and intellective processes can be projected outwards in the same way as sense perceptions; they are thus employed for building up the external world, though they should by rights remain part of the internal world. This may have some genetic connection with the fact that the function of attention was originally directed not towards the internal world but towards the stimuli that stream in from the external world, and that that function’s only information upon endo-psychic processes was received from feelings of pleasure and unpleasure. It was not until a language of abstract thought had been developed, that is to say, not until the sensory residues of verbal representation had been linked to the internal processes, that the latter themselves gradually became capable of being perceived.
Freud, Sigmund. Totem and Taboo: Some Points of Agreement between the Mental Lives of Savages and Neurotics. The Standard Edition of the Complete Psychological Works of Sigmund Freud. New York: W.W. Norton, 1989, 81