To Edward J . Steiner
Dear Dr. Steiner, 5 June 1958
No doubt it would be an excellent scheme to have a machine for recording the voices of spirits.
Unfortunately there are no cases on record where spirits had the good grace to present themselves as test persons.
Whatever else we can produce as spirit voices are those of mediums, and there the great trouble is to establish whether the communicated contents derive from ghosts or from unconscious fantasies of the medium or of any other member of the circle.
I would not go so far as to deny the possibility that a medium can transmit a ghostly communication, but I don't know in which way one can prove it, as such a proof is outside of our human possibility.
Your idea that any kind of phenomenon needs must represent a certain quantity of energy is-as far as our energy-concept goes-perfectly correct.
It is certainly true for the world of causal connections; but suppose, for the sake of the argument, an acausal arrangement of events, which is equally possible, since even causality is a statistical truth and not an axiom.
In that case we will try in vain to catch as much as a quantum of energy.
This whole question of so-called "occult phenomena" is nothing one could be naive about.
It is an awful challenge for the human mind.
C.G. Jung ~Carl Jung, Letters Vol. II, Page 444.