the second place, the
ideas of our dreams are presented in the form of images, which we are
unable to dismiss; we therefore mistake them for realities, exactly as
the sufferer from delirium tremens in waking life is apt to regard his
phantoms as real.

_Relations of Dreaming and Sleep._--It has been maintained by Hamilton
and others (see below, Modern Views) that dreams invariably accompany
sleep, and that we always find ourselves dreaming when we are awakened.
But even if it were true that dreams were invariably experienced at the
moment of waking, this would not by any means establish the invariable
concomitance of dreams and sleep of all sorts; at most it would show
that imperfect sleep is a condition of dreaming; in the same way, dreams
before wakening, known to have taken place either from the recollection
of the dreamer or from the observation of another person, may clearly be
due to imperfect wakening, followed by a deepening of sleep. It is,
however, by no means true that awakening from sleep is invariably
accompanied by a dream; in considering the question it must be
recollected that it is complicated by the common experience of very
rapid forgetfulness of even a vivid and complicated dream, only the fact
of having dreamt remaining in the memory; it is clear that amnesia may
go so far that even the fact of dreaming may be forgotten. On the whole,
however, there appear to be no good grounds for the assertion that we
always dream when we are asleep. On the other hand, there is no proof
that partial awakening is a necessary condition of dreaming.

_Representative Dreams._--Centrally initiated dreams may be due to a
kind of automatic excitation of the cerebral regions, especially in the
case of those clearly arising from the occupations or sensations of the
day or the hours immediately preceding the dream. To the same cause we
may attribute the recalling of images apparently long since forgotten.
Some of these revivals of memory may be due to the fact that links of
association which are insufficient to restore an idea to consciousness
in the waking state may suffice to do so in sleep. Just as a good
visualizer in his waking moments may call up an object never clearly
seen and yet distinguish the parts, so in sleep, as L. F. A. Maury
(1817-1892) and others have shown, an image may be more distinct in a
dream than it was when originally presented (see also below, Memory).

_Presentative Dreams._--The dreams due to