# On the Vital Principle/Book 2/Chapter 5

Let us now proceed, as those subjects have been scrutinized, to speak upon sensation in its widest acceptation.
Sensation is the combined result, as has been said, of a motion and an impression, for it seems to be some kind of change; and some writers maintain that it is only like which is impressionable by like, but we have already, in our treatises “upon action and impression,” shewn how far the opinion is or is not tenable. But it is difficult to understand why there is no sensation from the senses of themselves, that is, why, without the presence of external objects, the senses do not give out sensation, although fire, earth, and the other elements, from which or the accidents of which sensation is derived, are present in them. It is evident that it is because the sensibility is not in a state of activity, but is only in potentiality; and, therefore, that it is with it as with a combustible material, which alone, without something on fire, does not burn; for otherwise it might set fire to itself, and would stand in no need of fire, in reality, for the purpose. Since we speak of sentient perception in a two-fold ​sense, (for we speak of one who hears and sees, in potentiality, as “one hearing and seeing,” although he may happen to be asleep, and we say the same of one who is actually employing those senses,) so may sensation be spoken of in two ways, as subsisting in potentiality and subsisting in activity. Let us, however, before proceeding further, observe that impression, motion, and action are for us equivalent terms—for motion is a kind of action, although an action which is incomplete, as has been elsewhere explained. Now, all things which are impressed and set in motion are so affected by something capable of making impression and existing in activity; so that impression is in one sense by like, and in another sense by unlike, as we have said—for the unlike is subject to impression, but, having been impressed, it is converted into like. A distinction, however, must be drawn between the terms potentiality and reality, for we are now going to employ them in an absolute sense—any individual whatever, then, may be learned, as we might speak of any man as learned, because man is among beings capable of learning and being learned; and so we speak of a man as learned, from his actually professing, at the time, grammatical or other knowledge.
Thus, each of these individuals is learned in potentiality, although in a different manner—the one is so because he is of a certain genus and peculiar ​matter; and the other, because he can when he will reflect upon his knowledge, provided there is no external impediment to his doing so. It is this one only, however, when actually reflecting upon his knowledge, being in activity, and fully acquainted with some one subject, as A. for instance, who is to be accounted learned in reality. Both those first men, in fact, are learned in potentiality; but the one is so from having been modified by learning, and undergone frequent changes from one habit to an opposite one; and the other is so from possessing sensibility or rudimentary learning, and being able, although in a different manner, to pass from inertia to activity.
But the term impression is not absolute in signification, as sometimes it implies a kind of destruction by a contrary, and sometimes it signifies rather preservation of something being in potentiality by something which is in reality and like, in the relation that potentiality bears to reality. Thus, the possession of knowledge implies the power of reflecting upon it, and this either is not change, being but an increase of knowledge and a step towards its completion, or it is change of a different kind. It is not correct, therefore, to say that an individual, when thinking, is undergoing change, any more than that a builder, when employed in building, is undergoing change; so that the process by which an individual passes, as to his thinking and reflecting faculties, from potentiality to ​reality, ought to have some other appellation than that of instruction. We may not then, as has been observed, say of the individual who, from being in potentiality, learns and receives knowledge from one who is in reality and able to teach, that he suffers impression, or else it must be admitted that there are two modes of change, one in privative dispositions, and another over habits and nature. The first change, however, of this kind in the sentient being comes from the parent at the moment of conception; as from that moment the being has, as it were, learning and sensibility. There is an analogy between the state of activity and reflexion just alluded to, but with this difference, that the impressions productive of activity, as the audible, the visible, and others, are all derived from without; and the cause of this is that sensation, in activity, is employed upon particulars, knowledge upon universals; and universals are, in some way, in the Vital Principle itself. The act of thinking, therefore, is dependant only upon the will of the individual, which is not the case with sentient perception, as for it there must of necessity be objects to be perceived; and this holds good, and for the same reason, with respect to the sciences which are engaged upon external objects, because all such objects are among particulars, and are external to the percipient. But an opportunity may hereafter present itself for the further elucidation of the subject. ​Let it, for the present, suffice to say, that the expression being in potentiality has not an absolute signification, for it may be understood of a boy as being qualified potentially to be a General, and also of an individual of suitable age for the office; and the term sensibility is subject to like modifications of meaning. But as the distinction between these two states of sensibility is without any special appellation, although it has been shewn that there is a distinction between them and what the distinction is, it has been found necessary to employ the terms impression and change, as if their signification were unequivocal; but, as has been said, the sentient principle is, when in potentiality, analogous to the external object when in reality.
The sentient principle, in fact, suffers impression when unlike; but, having been impressed, it is converted into like, and becomes the same as that by which the impression is made.

## Notes

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​Note 1, p. 84. In our treatises upon action and impression, &c.] Some commentators have, in the treatises here alluded to, seen only a reference to other disquisitions, as those upon "'reproduction and destruction,' or decay," περὶ γενέσεως καὶ φθοράς; but as the passages which are cited do not meet the whole question, it has been suggested by Trendelenberg that the allusion may be to some other work which has not come down to us.
Note 2, p. 84. It is difficult to understand, &c.] In another chapter of this treatise, Aristotle has alluded to the power possessed by the senses of recalling former impressions; of realizing images at will, that is, without external objects. But the question here is to learn why the senses, which were supposed to be derived from the elements, from which or the accidents of which sensation itself was derived, are not in constant activity. The answer is, that the normal state, so to say, of the sensibility is potentiality, and that it is insusceptible, therefore, of perception, without impression by something from without to call it into action; just as the combustible material requires, in order to burn, the agency of fire. But the comparison contains a converse proposition, as while the material is required for the sensibility, it is fire, ​which may be regarded as the sensibility, which is required for the material.
Note 3, p. 84. Since we speak of sentient perception, &c.] These passages upon perception and sensation, which, in themselves, when deeply inquired into, are sufficiently obscure, are still less, if possible, apprehensible, on account of the wording and the attempted illustration by the leading terms, potentiality and reality. It is obvious, however, that we may and do speak of an individual as one who hears and sees, whether or not, at the moment, conscious of sound or colour; whether that is, awake or asleep, active or quiescent, in potentiality or reality. But an individual is, strictly speaking, only then seeing and hearing when he is actually sensible of colours and sounds; just as an individual, to use Aristotle's analogy, is only then to be accounted really learned, when actually reflecting upon and exercising some one special subject of knowledge. All attempts, however, to scrutinize the intimate operations, so to speak, of the sensibility under impression from without or excitation from within soon lose, even with the advanced knowledge of this age, the character of inductive science, and are lost, as in the text, in the maze of metaphysical abstractions. It seems to be the object of the argument to prove, that the sensibility, before being acted upon by external objects, such as light, sound, colour, &c., exists in potentiality and is unlike; when acted upon, it is raised to the state of reality, and
Note 4, p. 85. Before proceeding further let us, &c.] This and the following passages are but repetitions of what had been said, and further attempts at elucidation; they all too depend for a meaning upon the two great leading terms. For motion is in a two-fold state—when generated by impulse from without it is passive, when self-generated it is active; and that may be regarded as potential, this as real. Thus, if a body be at rest, before being impelled, the agent, by which it is impelled, is unlike and active; but, when so moved, it is, by the very act of motion, made active, and like to the agent.
Note 5, p. 85. But we must draw a distinction, &c.] These passages embody, in examples, the two terms so often alluded to, and exhibit the opposite conditions of human beings—every man is learned, potentially, because man is naturally so constituted as to be able to become learned, or, being learned, is subject to an eclipse of his learning by sleep, or disease, or inattention; and every man, endowed with the faculties of his nature, may acquire some one branch of learning, and, when there is no impediment to his doing so, by the exercise of that knowledge, become learned in reality.
The individual who is learned in the first sense cannot, without a succession of changes, (while passing, that is, from ignorance to knowledge), become, at will, learned, in reality; and he can, therefore, be accounted learned, only
Note 6, p. 86. The term impression, &c.] The same mode of illustration, through those two terms, is still continued—impression may be to an extent to destroy sensibility, and obliterate, of course, sensation, or it may be to that genial extent which raises, so to say, potentiality to reality, and renders the being conscious of external objects. So an individual, with knowledge yet potential, that is, possessed but not exercised, can, by reflecting upon it, without any change being wrought, render it a reality; for the possession of knowledge, like the endowment of sensibility, implies the self-same two-fold condition. Thus, the state of reflection is to acquired knowledge what external impressions are to sensibility; for, in either case, the agencies, when genial, occasion the transition from potentiality to reality; and so eliminate practical knowledge or perfect consciousness.
Note 7, p. 87. The first change, however, of this kind, &c.] It is not easy to perceive how this nascent condition can be a change, unless the first germ of being may be so regarded; and, indeed, it may be supposed, from the first moment, to have already, in potentiality, the powers which are yet to be developed. It may be, too, that this mysterious entity, along with the faculties and powers of its own nature, may involve the idiosyncrasy of the parent, for good or for ill; which was indeed exemplified in the life and death of the philosophical Montaigne. ​This capacity of the system for retaining dormant within it a something to be developed, by unknown causes, in time, is exemplified in the atom of virus, which, after an indefinite period, may, by mysterious agency, become a reality in the form of Hydrophobia. Well might the philosopher, when reflecting upon these incidents, exclaim, "Qui m'éclaircera de ce progrès, je le croirai d'autant d'autres miracles qu'il voudra."
Note 8, p. 86. So that the process by which an individual, &c.] This very obscure passage seems to intimate that, as instruction is only the development of faculties pre-existing and in potentiality, it is not to be regarded as an impression; for such an opinion would imply, instead of nature's ordinary process (development), a change from a privative state (ignorance), as well as change in habits of thought. This cannot, however, be insisted upon with much confidence; the French version is, "Done, ce qui fait passer l'être qui est en puissance à la realité parfaite, à l'entelechie, en fait d'intelligence et de pensée, doit s'appeller, non du nom d'apprentissage, mais d'un tout autre nom."
Note 9, p. 87. There is an analogy between, &c.] Sensation, that is, is to the body what reflection is to the mind, save that the one is produced by impression from without, and, therefore, not subject to the will, while the latter is the operation of will upon internal faculties. Thus, sensation admits a series of individual impressions which are to be analyzed and compared by the mental ​operation; and as the former becomes the parent of inductive, the latter is the source of deductive science.
Note 10, p. 88. Let it for the present suffice, &c.] An obvious distinction of potentiality—a boy is, potentially, qualified to be a general; that is, he has, by nature, faculties and powers which, when developed, will fit him for the office; and so is one who, although of suitable age, and whose faculties and powers are developed, may not yet have acquired the necessary military knowledge. An analogous distinction may be traced in sentient properties, but it is too evanescent for precise description; and the closing paragraph is a kind of summary of the conversion of the potential and unlike into the real and like.
* ↑ T. II. chap. 37.