To Markus Fierz

Dear Professor Fierz, 7 May 1945

Best thanks for your prompt and detailed answer, which I found very satisfactory.

I am particularly pleased with your suggested change on p. 25, which is much more promising than my version.

I quite agree with your view that the situation indicated in this sentence is similar to the situation in psychology where discrimination is the precondition of knowledge, only it seems to me a sidetrack which, though entirely right in itself, does not, as you yourself remark, quite fit into the context of my argument.

The ego-complex consists of all conscious contents, since consciousness is the exponent of the whole personality.

Hence its contents are also of a personal nature and must be distinguished from those of the objective psyche.

My argument is concerned with a more general reflection, namely the reconstruction of the physical process as a psychic process.

The parallel to this is the idea that the psychic process would, conversely, also be ”reconstructed” as a physical process.

The physical reconstruction would differ from the psychic in that it is not really a construction but would have to be conceived as an end-state or as an influence on the physical process, much as Schrodinger conceives it in his new English publication What Is Life?-an influencing of the physical processes by the psychic.

The materialistic premise is that the physical process causally determines the psychic process.

The spiritualistic premise is the reverse of this.

I think of this relationship in the physical sense as a reciprocal one, in which now one side and now the other acts as a cause.

One could also say that under certain conditions the physical process reflects itself in the psychic, just as the psychic does in the physical.

Of the utmost importance, it seems to me, is your information that the result of a measurement is essentially conditioned by the very nature of the measurement.

From this it is evident that an objective and absolute measurement is actually impossible.

Nevertheless a certain amount of measurement and a certain amount of knowledge of the physical are rendered possible by the psychic.

We would have to conclude that a certain molding and influencing of the physical process by the psychic are objectively present.

Whether this can be proved is naturally another matter.

If, faced with a reciprocal relationship, we can speak of an Archimedean point at all, then in my view such a point would be at least theoretically possible, since for the physical world there is an “outside” in the psychic, and consequently the physical would be an “outside” for the psychic at least in theory.

Your idea that the behaviour of physical processes is essentially conditioned by the physicist’s method and mode of observation is very interesting.

If we apply this idea to psychic processes, then psychological observation would also be prejudicial to the behaviour of the psyche.

In both cases the physical as well as the psychic would be needed. for the purpose of complementation, from which it follows that an approximately adequate knowledge of the physical could be completed by psychic complementation and, conversely, that any psychological knowledge could be completed only by knowledge of the physical.

In accordance with your view, psychology would be faced with the difficult task of explaining what the explanation of the physical as a psychic process actually means, and physics would be faced with the equally impossible task of explaining what are the physics of psychological theory.

Actually this seems to me possible only if, by a combination of physical and psychic knowledge, one could reach a plane above and beyond the present dichotomous mode
of observation by virtue of being in possession of both standpoints.

I have a vague recollection that Pauli once said something similar.

I still have a lot of thinking to do as regards your opinion that the moral commitment of psychological knowledge involves a crucial difference between this and the physicist’s knowledge.

At the moment I could not say anything adequate.

The moral “ought” is certainly, in itself, a genuine phenomenon, but whether it signifies a radical difference still seems to me somehow questionable.

Again with best thanks,

Yours sincerely,

C.G. Jung ~Carl Jung, Letters Vol. 1, Pages 365-367.

Note: The changed passage occurs in “Analytical Psychology and Education,” par. 163 : “As physics has to relate its measurements to objects, it is obliged to distinguish
the observing medium from the thing observed, with the result that the categories of space, time, and causality become relative.”

Note: F. wrote: “Therefore I do not know whether it is not just the mathematical unequivocality but the moral non-commitment of physics which can be understood
as a justification for the peculiar equivocality of psychology, which on the other hand is morally committed.”

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