On the Improvement of the Understanding
Observe that fiction regarded in itself, only differs from dreams in that in the latter we do not perceive the external causes which we perceive through the senses while awake. It has hence been inferred that representations occurring in sleep have no connection with objects external to us. We shall presently see that error is the dreaming of a waking man: if it reaches a certain pitch it becomes delirium. [B.S.]