Hallucination is not merely a pathological phenomenon but one that also occurs in the sphere of the normal.

 The history of prophecy as well as experiences among primitives show that psychic contents not infrequently come to consciousness in hallucinatory form.

In this respect only the form is worthy of note, not the function, which is nothing other than what is commonly called a “brain wave” [Einfall].

As the word itself indicates, a certain spontaneity attaches to the phenomenon; it is as though the psychic content had a life of its own and forced its way into consciousness by its own strength.

This peculiarity probably explains the ease with which the brain wave assumes an hallucinatory character.

Common speech is familiar with these transitions from brain wave to hallucination.

In the mildest cases we say: “I thought”; “it occurred to me” is a little stronger; stronger still is “it was as though an inner voice said,” and finally “it was as though someone were calling to me,” or “I heard a voice quite distinctly.”

Hallucinations of this kind usually derive from the still subliminal, maturer personality which is not yet capable of direct consciousness, as observations of somnambulists show.

In the case of primitive medicine-men they come from a subliminal thinking or intuiting which at that level is not yet capable of becoming conscious. ~Carl Jung, CW 18, Page 461