in dream-life, the scientific impulse to illuminate the less known by
the better known has long since begun to play on this obscure subject.
Even in the ancient world a writer might here and there be found, like
Democritus or Aristotle, who was bold enough to put forward a natural
and physical explanation of dreams. But it has been the work of modern
science to provide something like an approximate solution of the
problem. The careful study of mental life in its intimate union with
bodily operations, and the comparison of dream-combinations with other
products of the imagination, normal as well as morbid, have gradually
helped to dissolve a good part of the mystery which once hung like an
opaque mist about the subject. In this way, our dream-operations have
been found to have a much closer connection with our waking experiences
than could be supposed on a superficial view. The materials of our
dreams are seen, when closely examined, to be drawn from our waking
experience. Our waking consciousness acts in numberless ways on our
dreams, and these again in unsuspected ways influence our waking mental
life.[71] Not only so, it is found that the quaint chaotic play of
images in dreams illustrates mental processes and laws which are
distinctly observable in waking thought. Thus, for example, the apparent
objective reality of these visions has been accounted for, without the
need of resorting to any supernatural agency, in the light of a vast
assemblage of facts gathered from the by-ways, so to speak, of waking
mental life. I need hardly add that I refer to the illusions of sense
dealt with in the foregoing chapters.

Dreams are to a large extent the semblance of external perceptions.
Other psychical phenomena, as self-reflection, emotional activity, and
so on, appear in dream-life, but they do so in close connection with
these quasi-perceptions. The name "vision," given by old writers to
dreams, sufficiently points out this close affinity of the mental
phenomena to sense-perception; and so far as science is concerned, they
must be regarded as a peculiar variety of sense-illusion. Hence the
appropriateness of studying them in close connection with the illusions
of perception of the waking state. Though marked off by the presence of
very exceptional physiological conditions, they are largely intelligible
by help of these physiological and psychological principles which we
have just been considering.

_The State of Sleep._