To Professor Loewenthal
Dear Professor Loewenthal, 11 April 1947
I have read your letter with interest.
I think you are quite right when you correlate the concept of intro- and extraversion with all conceivable intro- and extrapetal tendencies.
My typology is based exclusively on biological data.
I have myself brought it into relationship with the biological fact that when many eggs are produced the protective instinct is little developed or not at all, whereas with few
eggs it is very strongly developed.
If you go into the ontogenetic and phylogenetic prehistory of intro- and extraversion, you necessarily come across all the polarities you mention.
At the same time the concept itself becomes increasingly generalized until it finally loses its psychological applicability.
But that is the fate of all psychological concepts.
If they are traced back to their biological foundations they become so imprecise that they lose their psychological meaning.
This is not to say that tracing types of consciousness back to instinctive data is superfluous.
To understand their structure a knowledge of the biological foundations is essential.
But since it is the nature of psychological concepts to point forwards, in the sense of an entelechy, their specific meaning consists in the apprehension of complicated
They lose this meaning, as said, when they are looked at retrospectively, in terms of their origin.
They then dissolve into extremely general biological conditions.
I don’t know whether you have read Jeans’s critique of Kant’s conception of space.
At any rate one would now have to formulate the apriorism of the so-called space category rather differently than was possible in Kant’s day.
The three-dimensionality of space is an unconscious precondition which is not to be confused with an apriori judgment.
This is where Jeans’s critique comes in, demonstrating that space cannot be an apriori judgment.
Its psychological reality is that of an archetype, i .e., it is just as unconscious as this and just as effective as this, which is why I have called the archetypes “dominants.”
It was just this point in your letter that interested me most, since at present I am very much concerned with apriori categories.
C.G. Jung ~Carl Jung, Letters Vol. 1, Pages 453-454.