Elements of the philosophy of the human mind. By Dugald Stewart. Rev. and abridged, with critical and explanatory notes, for the use of colleges and schools. By Francis Bowen ...

DREAMrING. 193
powers. From the observations which have been already made,
it is manifest that in sleep, the body is, in a very inconsiderable
degree, if at all, subject to our command. The vital and involuntary motions, however, suffer no interruption, but go on as
when we are awake, in consequence of the operation of some
cause unknown to us. In like manner, it would appear, that
those operations of the mind which depend on our volition are
suspended; while certain other operations are, at least, occasionally carried on. This analogy naturally suggests the idea, that
all our mental operations, which are independent of our will,
may continue during sleep; and that the phenomena of dreaniing may, perhaps, be produced by these, diversified in their
apparent effects, in consequence of the suspension of our voluntary powers.
If the appearances which the mind exhibits during sleep are
found to be explicable on this general principle, it will possess
all the evidence which the nature of the subject admits of.
How much power the will has over the thoughts. — It was
formerly shown, that the train of thought in the mind does not
depend immediately on our will, but is regulated by certain general laws of association. At the same time, it appeared, that
among the various subjects which thus spontaneously present
themselves to our notice, we have the power of' singling out
any one that we choose to consider, and of making it a particular object of attention; and that by doing so, we not only can
stop the train that would otherwise have succeeded, but firequently can divert, the current of our thoughts into a new
channel. It also appeared, that we have a power (which may
be much improved by exercise) of recalling past occurrences
to the memory, by a voluntary effort of recollection.
The indirect influence which the mind thus possesses over
the train of its thoughts is so great, that during the whole time
we are awake, excepting in those cases in which we fall into
what is called a revery, and suffer our thoughts to follow their
natural course, the order of their succession is always regulated
more or less by the will. The will, indeed, in regulating the
train of thought, can operate only (as I have already shown)
17