# On the Vital Principle/Book 3/Chapter 9

Since the Vital Principle of animals has been defined by the two faculties of judgment (which is the office of thought with sentient perception), and of locomotion, let us now, having dwelt sufficiently upon sensation and mind, proceed to consider, with respect to the motor power, what part of the Vital Principle it may be. Let us consider, that is, whether it is a part of Vital Principle and separate from it, substantively or abstractedly, or whether it is Vital Principle as a whole; and if it be a part, whether it is something peculiar and exclusive of those usually attributed to Vital Principle, and which have been alluded to, or whether it is to be considered as one of them.
But a difficulty at once presents itself, both in ​determining the sense in which we are to speak of the parts of Vital Principle, and in settling how many of them there may be. In one point of view, in fact, the parts appear to be infinite in number and to comprise, not only those which some speak of as the reasoning, passionate and appetitive, and others as the rational and the irrational, but other parts also, which by the distinctions employed in those classifications, are brought into notice, and are more broadly distinguished from one another than are any of those to which we have alluded. Those other parts are the nutritive, which belongs to all plants and animals, and the sentient, which cannot readily be placed among either rational or irrational parts; there is the imaginative, besides, which differs in mode of being from all the others, and yet it would be difficult to determine, amid the several parts of Vital Principle, with which of them it is identical, or from which it differs. Besides these, there is the appetitive part, which, whether considered abstractedly or functionally, would seem to differ from all others, and yet it would be absurd to separate it from them; for volition is present in the rational, as decire and passion are in the irrational part, and if the Vital Principle be made up of these three, appetite must be present in each of them.
But, to resume the more especial topic of this chapter, what is that, let us ask, which confers upon ​an animal locomotive power? Now, it may be supposed that the generative and the nutritive functions, which are innate in all living beings, originate the motion concerned in the processes of growth and decay, which equally belong to them all; and with respect to breathing and expiration, sleep and watching, which are subjects of much difficulty, we shall enter upon the consideration of them hereafter. Let us, however, consider what confers upon an animal the power of progression.
Now, it clearly is not the nutritive faculty—for the movement of progression is ever for some end, and is associated either with imagination or appetite; and then no being moves unless urged to it by desire or fear, excepting, indeed, there be impulse from without; plants, besides, were nutrition the cause, should be locomotive, and possess some organ to fit them for that kind of movement.
Neither can it be the sentient faculty—for there are many creatures which are sentient, and yet stationary throughout their existence; and if nature do nothing in vain, and never, except in the case of beings dwarfed or deformed, omits anything necessary to existence, the creatures alluded to are perfect creatures; and as proof of this they are reproductive, are capable of development and subject to decay, so that they also ought to have organs to fit them for progression.
​Neither can the rational faculty or the so-called mind be the motor power, for the speculative intellect never thinks upon what is to be done, or suggests aught concerning what should be fled from or pursued after; but this motion is the act of one fleeing from or pursuing after something. Nor does that faculty, even when reflecting upon any such object, at once bid to flee from or to follow after it, as it often dwells upon something terrible, or agreeable, without suggesting alarm, although the heart may be set in motion or some other part of the impression be agreeable. Add to this, that although the mind may bid, and the reason suggest that something should be fled from or pursued after, the individual does not necessarily move, but acts as does an intemperate person, according to the dictates of passion. It is thus, occasionally, we see that a physician, although versed in medical science, does not cure, as if there were something other than the science which had the power of acting according to the precepts of the science.
It may be affirmed that the appetite cannot be the positive cause of this motion; for the temperate, even while desiring and yearning after something, do not act in order to secure that for which they feel appetite, but follow their understanding.

## Notes

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​Note 1, p. 173. But a difficulty at once presents itself, &c.] There is an apparent want of discrimination here between the faculties which are the privilege and distinction of higher creatures and the functions which are essential to life, and without which there can be neither animal nor living being. In a subsequent paragraph the rational faculty or mind (καὶ ὁ καλούμενος νοῦς) is excluded from all participation in corporeal movements, and held to have no part in sentient perception. It is ​supposed, in fact, never to be engaged upon what is practical as its office is contemplation, so that, "when dwelling upon what may be fearful, or otherwise, it does not, at once, suggest, flight or pursuit;" although, independently of its influence, "the heart or some other organ of the body may be accelerated or depressed." But in all this, as no allusion is made to a moving force, whether the motive be imagination or the stimulus of appetite, the inquiry may be said to be defective.
Note 2, p. 173. But to resume the more especial, &c.] Although these passages, which allude both to physical and moral causes of motion, are sufficiently obvious, yet, as they do not explain how locomotion is effected, they fail in the object of the inquiry; and then the motion concerned in nutrition, growth and decay, is almost in the same category, so to say, with that of progression. It may be mentioned that the "motion and progression of animals," "breathing and expiration," "sleep and watching," "youth and age," are special treatises, and probably composed for the elucidation of this particular work upon "life." The comparison between the intemperate man who, although rational, acts against his reason, and the physician who, although versed in medical science, does not cure, seems to exemplify the adage, that to advise is one thing, to do, another; or to confirm the solemn words of Johnson, "that teachers of morality discourse like angels, but they live like men."