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American Imago 61.3 (2004) 305-317
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From Elements of the Philosophy of the Human Mind (1792)
The powers dependent on volition suspended during sleep. From a consideration of these facts, it seems reasonable to conclude that in sleep those operations of the mind are suspended which depend on our volition; for if it be certain that before we fall asleep we must withhold, as much as we are able, the exercise of all our different powers, it is scarcely to be imagined that, as soon as sleep commences, these powers should again begin to be exerted. The more probable conclusion is that when we are desirous to procure sleep, we bring both mind and body, as nearly as we can, into that state in which they are to continue after sleep commences. The difference, therefore, between the state of the mind when we are inviting sleep, and when we are actually asleep, is this—that in the former case, although its active exertions be suspended, we can renew them, if we please. In the other case, the will loses its influence over all our powers, both of mind and body; in consequence of some physical alteration in the system, which we shall never, probably, be able to explain.
In order to illustrate this conclusion a little further, it may be proper to remark that if the suspension of our voluntary operations in sleep be admitted as a fact, there are only two suppositions which can be formed concerning its cause. The one is that the power of volition is suspended; the other, that the will loses its influence over those faculties of the mind, and those members of the body, which, during our waking hours, are subjected to its authority. If it can be shown, then, that the former supposition is not agreeable to fact, the truth of the latter seems to follow as a necessary consequence.
1. Volition itself not suspended during sleep. That the power of volition is not suspended during sleep appears from the efforts [End Page 305] which we are conscious of making while in that situation. 305We dream, for example, that we are in danger; and we attempt to call out for assistance. The attempt, indeed, is, in general, unsuccessful; and the sounds which we emit are feeble and indistinct; but this only confirms, or rather is a necessary consequence of the supposition, that, in sleep, the connection between the will and our voluntary operations is disturbed or interrupted. The continuance of the power of volition is demonstrated by the effort, however ineffectual.
In like manner, in the course of an alarming dream, we are sometimes conscious of making an exertion to save ourselves, by flight, from an apprehended danger; but in spite of all our efforts, we continue in bed. In such cases, we commonly dream that we are attempting to escape, and are prevented by some external obstacle; but the fact seems to be that the body is, at that time, not subject to the will. During the disturbed rest which we sometimes have when the body is indisposed, the mind appears to retain some power over it; but as, even in these cases, the motions which are made consist rather of a general agitation of the whole system, than of the regular exertion of a particular member of it, with a view to produce a certain effect; it is reasonable to conclude that in perfectly sound sleep the mind, although it retains the power of volition, retains no influence whatever over the bodily organs.
In that particular condition of the system, which is known by the name of incubus (or nightmare), we are conscious of a total want of power over the body; and, I believe, the common opinion is that it is this want of power which distinguishes the incubus from all the other modifications of sleep. But the more probable supposition seems to be that every species of sleep is accompanied with a suspension of the faculty of voluntary motion, and that the incubus has...