"Freud seems constantly to be influenced by the thought that a hallucination is something requiring a tremendous mental force - seelische Kraft. (...) And he thinks that the only force strong enough to produce the hallucinations of dreams is to be found in the deep wishes of early childhood. One might question this. Supposing it is true that hallucinations in waking state require an extraordinary mental force - why should not dream hallucinations be the perfect normal thing in sleep, not requiring any extraordinary force at all?"
Wittgenstein, Lectures & Conversations on Aesthetics, Psychology
and Religious Belief. Edited by Cyril Barrett. University of California
Press, Berkeley and Los Angeles, p. 50.