This book-my last-was begun more than ten years ago. I first got the idea of writing it from C. Kerényi's essay on the Aegean Festival in Goethe's Faust.1 The literary prototype of this festival is The Chymical Wedding of Christian Rosencreutz, itself a product of the traditional hierosgamos symbolism of alchemy. I felt tempted, at the time, to comment on Kerényi's essay from the standpoint of alchemy and psychology, but soon discovered that the theme was far too extensive to be dealt with in a couple of pages. Although the work was soon under way, more than ten years were to pass before I was able to collect and arrange all the material relevant to this central problem.
— Carl Gustav Jung
Jung wrote this preface in his eighty-first year, describing a decade-long accumulation of alchemical material as if the work had simply demanded more room than he had initially granted it. What is easy to pass over is the seed: Kerényi's essay on Goethe's Aegean Festival, itself a commentary on a literary carnival that reaches back to the *hierosgamos*, the sacred marriage. One idea inside another inside another — and at each layer, the same problem: what happens when opposites are brought into contact rather than held apart by doctrine or defended by one side defeating the other?
The *Mysterium Coniunctionis* is where Jung pressed hardest against the tendency — his own as much as anyone's — to resolve tension too quickly, to let the spirit-side of any polarity absorb the soul-side rather than hold both until something third and unreduced emerged. That the book began with a carnival and a wedding and an alchemical pamphlet from 1616 is not incidental. The *hierosgamos* is specifically not a triumph of light over dark; it is a meeting that transforms both parties without erasing either. Ten years of collecting material is what it costs to resist the easier outcome.
Carl Gustav Jung·Mysterium Coniunctionis: An Inquiry into the Separation and Synthesis of Psychic Opposites in Alchemy·1955