The artist is not the only person involved in looking at a picture; recognition of what the picture represents could not occur if the observer were to rely exclusively on his sense of smell. The wider his experience of art the more likely he would be to interpret the painting correctly. In many pictures the effectiveness of the representation would depend on perspective. In Euclidean geometry definitions of terms such as “point”, “straight line” and “circle” are so closely wedded to marks on paper and similar realizations that these definitions, which are really suggestive descriptions, serve well enough. Since psycho-analysis will continue to develop people cannot speak of invariants under psycho-analysis as if psycho-analysis were a static condition. Psychotic mechanisms appear in the course of a psychoanalytically controlled breakdown, but the analyst may be called upon to deal with them after such a breakdown has occurred, or, because something has happened, to precipitate such a breakdown during analysis.