It is remarkable that S. Freud, who invented psychoanalysis, the analysis of the psyche, never gave any definition of the psychical. Each time he had to make a statement about it he said there was no point because everyone knew intuitively or by experience what he meant. The real problem with the developmental perspective is not the journey from two to three—from the dyad to the triad—but the transition from the stage of potential thirdness to effective thirdness when he is perceived as a distinct object by the child. C. S. Peirce says, in a letter to Lady Wellby, "Thirdness is the triadic relation existing between a sign, its object and the interpreting thought, itself a sign, a sign that mediates between the interpreter and its origin". In thirdness there is always one term that is disturbing by being undesirable or unwanted, or one missing term that would change the triangular structure to form two pairs.