It has long been known that some years prior to the publication of 'Psychological Types', Jung carried on a correspondence with his colleague and former analysand, Hans Schmid-Guisan, dealing exactly with the question of psychological types. Already around the time of the publication of Jung's 'Psychological Types' there was talk of publishing this correspondence, and such considerations naturally emerged again during the years where Jung's Collected Words were being collected with the aim of committing them to print.
On both occasions, however, Jung personally vetoed the publication of these letters, stating that they were of “a highly technical nature” and that they would only “cause more confusion” than they would create clarity. Nonetheless, history tends to have little mercy for the posthumous wishes of writers and, as a rule, what has not been committed to the flames will tend to see publication sooner or later. As such, the letters in question now lie before us and already from the first pages of the correspondence, one suspects that Jung may have had ulterior motives for denying their publication as well.