Strictly speaking, projection is never made; it happens, it is simply there.
In the darkness of anything external to me I find, without recognizing it as such, an interior or psychic life that is my own.
It would therefore be a mistake in my opinion to explain the formula “tarn ethice quam physice” by the theory of correspondences, and to say that this is its “cause.”
On the contrary, this theory is more likely to be a rationalization of the experience of projection.
The alchemist did not practise his art because he believed on theoretical grounds in correspondence; the point is that he had a theory of correspondence because he experienced the presence of pre-existing ideas in physical matter.
I am therefore inclined to assume that the real root of alchemy is to be sought less in philosophical doctrines than in the projections of individual investigators.
I mean by this that while working on his chemical experiments the operator had certain psychic experiences which appeared to him as the particular behaviour of the chemical process.
Since it was a question of projection, he was naturally unconscious of the fact that the experience had nothing to do with matter itself (that is, with matter as we know it today).
He experienced his projection as a property of matter; but what he was in reality experiencing was his own unconscious.
In this way he recapitulated the whole history of man’s knowledge of nature.
As we all know, science began with the stars, and mankind discovered in them the dominants of the unconscious, the “gods,” as well as the curious psychological qualities of the zodiac: a complete projected theory of human character.
Astrology is a primordial experience similar to alchemy. Such projections repeat themselves whenever man tries to explore an empty darkness and involuntarily fills it with living form. ~Carl Jung, CW 12, Para 346