deprived of objects that move it visibly, does not, however, cease to
have ideas--to be set in activity--to be modified in a manner that is
sufficiently sensible--to have an influence upon his body. But if a
little reflection be called in, the solution to this difficulty will be
found: it will be perceived that, even during sleep, his brain is
supplied with a multitude of ideas, with which the eye or time before
has stocked it; these ideas were communicated to it by exterior or
corporeal objects, by which they have been modified: it will be found
that these modifications renew themselves, not by any spontaneous, not
by any voluntary motion on its part, but by a chain of involuntary
movements which take place in his machine, which determine, which excite
those that give play to the brain; these modifications renew themselves
with more or less fidelity, with a greater or lesser degree of
conformity to those which it has anteriorly experienced. Sometimes in
dreaming, he has memory, then he retraces to himself the objects which
have struck him faithfully;--at other times, these modifications renew
themselves without order, and without connection, very differently from
those, which real objects have before excited in his interior organ. If
in a dream he believes he sees a friend, his brain renews in itself the
modifications or the ideas which this friend had formerly excited--in
the same order that they arranged themselves when his eyes really beheld
him--this is nothing more than an effect of memory. If in his dream he
fancies he sees a monster which has no model in nature, his brain is
then modified in the same manner that it was by the particular, by the
detached ideas, with which it then does nothing more than compose an
ideal whole; by assembling, and associating, in a ridiculous manner, the
scattered ideas that were consigned to its keeping; it is then, that in
dreaming he has imagination.

Those dreams that are troublesome, extravagant, whimsical, or