On the Vital Principle/Book 3/Chapter 1
We may be satisfied, from the observations which follow, that there is no sense besides the five—besides, that is, Sight, Hearing, Smell, Taste, and Touch; for if Touch be the sense for every impression of which we are sensible, and if we have this sense, then, as all the conditions of whatever is tangible, in so far as tangible, are made perceptible to us by the Touch, it follows that, if any sensation be wanting, some sentient organ must be wanting to us also. Now, all the bodies which are perceived by touching are made sensible to us by the Touch which has been allotted to us; and all those which are perceived, not by touching but, through media, are made sensible to us by simple bodies—that is, by air and water. We are so constituted, in fact, that, if several objects, differing generically from one another, could be perceived through one medium, an individual, having a sentient organ such as that medium, would, necessarily, be sensible of impressions through both media—as if the sentient organ should be of air, then, as air is the medium for sound and colour, the individual would be sensible of both impressions through the same organ. Should there, however, be more than one medium for the transmission of the same impression, as air as well as water (since both are diaphanous,) serves for the transmission of colour, then an individual, having an organ constituted of either of those elements, would perceive impressions transmitted through them both. The sentient organs, however, are constituted of those two simple bodies, air and water, exclusively—for the pupil is of water, the hearing of air, and the smell either of one or other; but fire forms no part of any organ, or rather it is an element common to all, as there is nothing sentient without heat; and earth either does not enter at all into any sentient part, or it has been in some especial and peculiar manner combined with the Touch. Thus, there can remain only this conclusion, that, were there no air or water, there could be no sentient organ; and organs so constituted are actually possessed by animals now living. All the senses, in fact, are possessed by animals which are neither imperfect nor mutilated; for the mole appears to have eyes beneath its skin. So that, unless there is some kind of body hitherto unknown and some kind of impression unsuited to bodies here on earth, it may be affirmed that no sense can be wanting to us. But neither is it possible that there should be any special organ for the perception of common properties, (such as motion, rest, magnitude, form, number and unity), of which we are made sensible, by each special sense, accidentally; for we perceive all such by motion as we do magnitude, and as we do form, as form is a kind of magnitude; the state of rest we are sensible of by the absence of motion, and number we perceive by the want of continuity and by particular senses, for each sense is perceptive of unity. So that, evidently, there cannot be a peculiar sense for the perception of any one of those properties, as motion, for instance; with respect to which we shall be ever situated as we now are, when, by sight, we judge of something sweet. And this we are able to do from our happening to possess a sense which is perceptive of double impressions, and by the way in which those impressions coincide, we recognise what the thing is; were this not the case, then, in no wise, except by chance, could we perceive that the thing was sweet, any more than we could tell that an individual is the son of Cleon, not because he is really so, but because he is fair; and fairness is an accident pertaining to the son of Cleon. And yet we have a common sense for the perception of common properties and that not casually, although it is not a peculiar sense; for, were it so, then in no otherwise could we perceive those properties than, as has just been said, we see that an individual is the son of Cleon. The senses, however, do perceive, casually, the special qualities of each other; but then they do so, not as distinct senses but, as becoming one sense, as when double impressions may be made simultaneously upon the same organ, as by bile, which is bitter and yellow. But as it belongs not to either sense to say that both qualities belong to one substance, we are exposed to error, and led to think that if a fluid be yellow it must be bile.
Should any one inquire why we have been furnished with several senses in place of having only one, it might be answered, " that we have so been constituted in order that the sequences and common properties of bodies, as motion, magnitude, and number, may the less readily escape our notice." If vision, in fact, were our only sense and it perceptive only of whiteness, then all other qualities would more readily escape our notice and seem to be identical, on account of colour and magnitude being in an invariable sequence to one another. But as here common properties are manifested in different bodies, it is evident that each of those properties (colour and magnitude) must also be different.
Notes
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Note 1, p. 131. The sentient organs, however, are constituted, &c.] The senses were formed, according to that age, from the elements—as the hearing from air, and the eye, which alone was supposed to have a special organ, from the purest part of the fluid secreted by the brain; and vision is the result, according to Aristotle, of refraction. Thus, Democritus[1] was held to be right in saying that the eye is water but to be wrong in supposing vision to be caused by reflection, (τὸ ὁρᾶν εἶναι τὴν ἔμφασιν) as vision is, not in the eye but, in the percipient; for "vision is refraction" (ἀνάκλασις γὰρ τὸ πάθος). Aristotle shews that, according to the admitted doctrines, these two elements only constitute the sentient organs of all animals which are perfect; and adds, as if to guard against a possible objection, that the mole has eyes although they may not be very apparent. It is then argued that, unless there is some kind of body or mode of impression different from all with which we are acquainted, no sense can be wanting; and Cuvier[2] adopted a similar argument to prove that no animal, unknown to Zoology, remains to be discovered.
Note 2, p. 132. And this we are able to do, &c.] This passage is elliptical and obscure; but, as "the relative is too closely connected with the example something sweet to admit of being separated," it may imply that the sight may, by colour and refraction, determine the quality of a particular fluid. But, as no sense can judge, excepting indirectly, of compound qualities, the perception of such is accidental, a kind of guess, that is, just as it would be in the case of a fair individual, in the example of Cleon's son.
Note 3, p. 133. The senses, however, do perceive casually, &c.] This passage remains, according to its wording, unintelligible, notwithstanding the attention bestowed upon it by commentators, because of the difficulty of attaching any sense to the assumption, that the senses can become as one. The comment "si unum et idem uno et eodem tempore a diversis sensibus percipitur, ni sensus in unum coalescunt," assumes but does not shew that the senses can so coalesce, and then judge of impressions made upon them individually. And thus here again is required a central organ, the common origin of the perceptive power of the senses, to which all impressions are to be referred and by which they are to be compared; and such an organ is the brain. But still, from the moment that we judge of more than a simple impression or a single idea, there is liability to error, as was observed and exemplified in the case of a fluid, which, from being bitter and yellow, is at once assumed to be bile because those are the known qualities of that fluid. Many of our errors arise, no doubt, in like manner, from our not sufficiently scrutinising the impressions derived from external objects.