The book on types yielded the insight that every judgment made by an individual is conditioned by his personality type and that every point of view is necessarily relative. This raised the question of the unity which must compensate this diversity, and it led me directly to the Chinese concept of Tao.

A subject with which I had been deeply concerned ever since my book Psychology of the Unconscious was the theory of the libido. I conceived the libido as a psychic analogue of physical energy, hence as a more or less quantitative concept, which therefore should not be defined in qualitative terms. My idea was to escape from the prevailing concretism of the libido theory–in other words, I wished no longer to speak of the instincts of hunger, aggression, and sex, but to regard all these phenomena as expressions of psychic energy.

In physics, too, we speak of energy and its various manifestations, such as electricity, light, heat, etc. The situation in psychology is precisely the same. Here, too, we are dealing primarily with energy, that is to say, with measures of intensity, with greater or lesser quantities. It can appear in various guises. If we conceive of libido as energy, we can take a comprehensive and unified view. Qualitative questions as to the nature of the libido–whether it be sexuality, power, hunger, or something else–recede into the background. What I wished to do for psychology was to arrive at some logical and thorough view such as is provided in the physical sciences by the theory of energetics. This is what I was after in my paper “On Psychic Energy” (1928). I see man’s drives, for example, as various manifestations of energic processes and thus as forces analogous to heat, light, etc. Just as it would not occur to the modern physicist to derive all forces from, shall we say, heat alone, so the psychologist should beware of lumping all instincts under the concept of sexuality. This was Freud’s initial error which he later corrected by his assumption of “ego-instincts.” Still later he brought in the superego, and conferred virtual supremacy upon it.

As I worked with my fantasies, I became aware that the unconscious undergoes or produces change. Only after I had familiarized myself with alchemy did I realize that the unconscious is a process, and that the psyche is transformed or developed by the relationship of the ego to the contents of the unconscious. In individual cases that transformation can be read from dreams and fantasies. In collective life it has left its deposit principally in the various religious systems and their changing symbols. Through the study of these collective transformation processes and through understanding of alchemical symbolism I arrived at the central concept of my psychology: the process of individuation.

Man always has some mental reservation, even in the face of divine decrees. Otherwise, where would be his freedom? And what would be the use of that freedom if it could not threaten Him who threatens it?