424a 16-424b 20
BOOK II, CHAPTER XII
GENERAL CONCLUSIONS
ON SENSATION
IT must be taken as a general rule that all sensation is the receiving of forms without matter, as wax receives a seal without the iron or gold of the signet-ring. It receives an imprint of the gold or bronze, but not as gold or bronze. Similarly the sense of any sense-object is acted upon by a thing having colour or flavour or sound; not, however, in respect of what each is called as a particular thing, but in so far as each has a certain quality and according to its informing principle. Secs. 551-4
The primary sensitive part is that in which a power of this sort resides. They [part and power] are indeed the same thing, but differ in mode of being. What receives sensation will be an extended magnitude, but neither being sensitive nor sensation is a magnitude. Each is, rather, a certain ratio and power of a magnitude. Sec. 555
It is clear from these facts why the excess of sensible qualities destroys the sense-organs. For if the change is too violent for the sense-organ, the ratio [of the latter] is lost,--which [ratio] is the sense. It is as with tone and harmony when the strings are violently struck. Also it is plain why plants have no sensation, though they have some share in soul, and are affected by tangible objects to become hot or cold. The reason is that they lack a mean or principle of this kind, able to receive the forms of sense-objects; they are acted upon materially. Secs. 556-7
It might be asked, is anything affected by odour if it cannot have the sense of smell?--or by colour, if it is unable to see? And so in the other cases. Sec. 558
But if what can be smelt is odour, whatever causes smell is odour.[ Or 'whatever odour causes, it causes smelling'. St. Thomas notes both senses, Sec. 559.] Hence things incapable of smelling cannot be affected by odour. The same argument holds for the other senses. And of subjects that can perceive, the ability belongs to them only in virtue of each being sensitive. Sec. 559
The same is evident thus: neither light or darkness or sound or odour affect bodies; but only what they occur in does so; e.g. it is the air which accompanies thunder that smashes trees. Sec. 560
But things tangible and savours do so affect things. If not, what is it that inanimate things are affected and changed by?[ If Aristotle is here putting an objection to his own view, St. Thomas misses this nuance ( Sec. 561). He takes this objection to be simply Aristotle's statement of one aspect of the matter as he saw it.] Sec. 561
Therefore, do not also the other sense-objects have a like effect? But not every body is affected by odour or sound,--such recipients being only things indefinite and unstable like air: which may smell as though affected somehow. Sec. 562
What then is to smell, save to be 'affected somehow'? But to smell is to sense. Air, however, being so affected, becomes rapidly sensible. Sec. 563
ST. THOMAS'S COMMENTARY
LECTIO TWENTY-FOUR
Sec. 551. Having examined each of the senses separately the Philosopher proceeds now to conclusions about sensitivity in general; and this in three stages: first he explains the nature of sense; then, at 'It is clear',[ 424a 28.] he solves certain problems connected with that explanation; and thirdly, at 'It might be asked',[ 424b 2.] he raises certain questions touching the way a sense is affected by its object. As regards the first point he explains (a) the nature of sense, and (b) the nature of sense-organs, at 'The primary sensitive part'.[ 424a 24.]
First, then, he says that it must be maintained in general, as true of all the senses without exception, that the senses receive forms without matter, as wax receives the mark of a ring without the iron or gold. This, however, would seem to be common to all cases of passive reception; every passive thing receives from an agent in so far as the agent is active; and since the agent acts by its form, not its matter, every recipient as such receives form without matter. Which indeed is sensibly apparent; e.g. air does not receive matter from fire acting upon it, but a form. So it would seem not to be peculiar to sensation that it receives form without matter.
Sec. 552. I answer that, while it is true that every recipient receives a form from an agent, there are different ways of receiving form. Form received in a patient from an agent sometimes has the same mode of existence in the recipient as in the agent; which occurs when the patient is disposed to the form in the same way as the agent. For whatever is received is received into the being of the recipient; so that, if the recipient is disposed as the agent is, the form comes to be in the recipient in the manner in which it exists in the agent. And in this case the form is not imparted without the matter. For although the numerically one and the same division of matter that is in the agent does not become the recipient's, the latter becomes, in a way, the same as the material agent,[ i.e. the same as the agent in respect of its materiality as well as of its form.] inasmuch as it acquires a material disposition like that which was in the agent. And it is in this way that air receives the influence of fire, and any other passive thing in Nature the action that alters its natural quality.
Sec. 553. Sometimes, however, the recipient receives the form into a mode of existence other than that which the form has in the agent; when, that is, the recipient's material disposition to receive form does not resemble the material disposition in the agent. In these cases the form is taken into the recipient 'without matter', the recipient being assimilated to the agent in respect of form and not in respect of matter. And it is thus that a sense receives form without matter, the form having, in the sense, a different mode of being from that which it has in the object sensed. In the latter it has a material mode of being,[ esse naturale.] but in the sense, a cognitional and spiritual mode.
Sec. 554. Aristotle finds an apt example of this in the imprint of a seal on wax. The disposition of the wax to the image is not the same as that of the iron or gold to the image; hence wax, he says, takes a sign, i.e. a shape or image, of what is gold or bronze, but not precisely as gold or bronze. For the wax takes a likeness of the gold seal in respect of the image, but not in respect of the seal's intrinsic disposition to be a gold seal. Likewise the sense is affected by the sense-object with a colour or taste or flavour or sound, 'not in respect of what each is called as a particular thing',[ Oxford transl.: 'it (the sense) is indifferent what in each case the substance is', 424a 23-4.] i.e. it is not affected by a coloured stone precisely as stone, or sweet honey precisely as honey, because in the sense there is no such disposition to the form as there is in these substances; but it is affected by them precisely as coloured, or tasty, or as having this or that 'informing principle'[ vel secundum rationem, i.e. sec. formam.] or form. For the sense is assimilated to the sensible object in point of form, not in point of the disposition of matter.
Sec. 555. Next, at 'The primary sensitive part',[ 424a 24.] he concludes about the organ of sense. Since from his teaching that sense receives forms into cognition immaterially, which is true of the intellect also, one might be led to suppose that sense was an incorporeal faculty like the intellect, to preclude this error Aristotle assigns to sense an organ, observing that the 'primary sensitive part', i.e. organ of sense, is that in which a power of this sort resides, namely a capacity to receive forms without matter. For a sense-organ, e.g. the eye, shares the same being with the faculty or power itself, though it differs in essence or definition, the faculty being as it were the form of the organ, as was said above.[ Secs. 234-41.] So he goes on to say 'an extended magnitude', i.e. a bodily organ, is 'what receives sensation', i.e. is the subject of the sense-faculty, as matter is subject of form; and yet the magnitude and the sensitivity or sense differ by definition, the sense being a certain ratio, i.e. proportion and form and capacity, of the magnitude.
Sec. 556. Then, when he says 'It is clear etc.',[ 424a 28.] he infers from these premisses a reply to two questions which might arise. What has been said, he observes, explains why an excess in the object destroys the sense-organ; for, if sensation is to take place there must pre-exist in the organ of sense 'a certain ratio'[ ratio, cf. Sec. 555.] or, as we have termed it, proportion. But if the impact of the sense-object is stronger than what the organ is naturally able to bear, the proportion is destroyed and the sense itself, which precisely consists, as has been said, in the formal proportion of the organ, is neutralised. It is just as though one were to twang cords [ i.e. of some stringed instrument.] too violently, destroying the tone and harmony of the instrument, which consists in a certain proportion.
Sec. 557. His analysis also gives us the answer to another question, namely why plants do not feel, though they have some share in soul and are affected by certain sense-objects, i.e. tangible things, as well as by heat and cold. The reason why they do not feel is that they lack the proportion needed for sensation, in particular that balance between extremes of the tangible qualities which is a prequisite of the organ of touch, apart from which there can be no sensation. Hence they have no intrinsic principle for receiving forms 'apart from matter', that is to say, no sense. They are affected and undergo changes only materially.
Sec. 558. Next, when he says 'It might be asked'[ 424b 2.] he raises a question touching the sense-object's action on the senses. Having just remarked that plants are affected by certain sense-objects, he raises the question whether a subject can ever be affected by objects other than those of which it possesses the sense; say, by odour if it has no smell, or by colour, if it has no sight, or by sound, if it is without hearing.
Sec. 559. Then, at 'But if what can be smelt is odour',[ 424b 6.] he brings two reasons against this suggestion. In the first place, it is proper to what can be smelt to cause smell; but odour is such; therefore if anything causes smell, it causes it by odour (or, according to another reading, odour causes smell). The proper action of odour as such is to cause a smell or occasion a smelling. Whence it follows that whatever receives the activity of odour as such has a sense of smell; and whatever lacks a sense of smell cannot be affected by odour. And the same argument holds of other beings that it is impossible that anything whatever might be affected by sense-objects; this can only happen in things endowed with sense.
Sec. 560. At 'The same is evident thus'[ 424b 9.] he states the second reason, as follows. The above argument is confirmed by experience. Light and darkness, smell and sound, produce no effect on sensible bodies, except incidentally, inasmuch as the bodies with those qualities do something, like the air that cleaves wood when it thunders; for it is not this sound that affects the wood, but the moving air.
Sec. 561. Then at 'But things tangible and savours'[ 424b 12.] he shows that it is otherwise with tangible qualities; tangible things and 'savours', i.e. flavours, do indeed produce, he says, an effect on sensible objects. But this is to be understood of the flavours, not precisely as such, i.e. as tasteable, but just in so far as the tasteable is something tangible, and taste a kind of touch. For if (insensible)[ Si . . . corpora insensibilia non paterentur, etc.] bodies were not affected by tangible qualities, there would be no question of inanimate bodies being affected and altered at all, these tangibles being the elemental active and passive qualities in virtue of which all bodily alterations take place.
Sec. 562. Next, at 'Therefore, do not also',[ 424b 14.] he shows that other sense-objects act on inanimate things, though not on all. For in asking: 'Therefore, do not' other sense-objects affect inanimate things as odour does?, he implies that they do. Yet not every body is affected by odour and sound, though all are by heat and cold. By such sense-objects are affected only unstable, impermanent bodies, such as air and water, which, being fluid, are not very self-contained; and that air can be affected by odour is obvious enough when it stinks.[ foetet.] Another reading says 'bears',[ feret.] meaning that the phenomenon [ species: presumably the odour.] is carried or borne to the sense by sensible objects other than itself.[ Presumably, in this case, the air.] The reason for this difference is that, as tangible qualities are productive of the other sensible qualities, they have more active power than the others, and can operate on bodies in general, whereas the other sense-objects, having less active power, can act only on things that are especially impressionable. The same principle applies to the light of the heavenly bodies, with its effect on terrestrial ones.
Sec. 563. Lastly, at 'What then is to smell?',[ 424b 16.] he solves the problem raised by the argument stated above. If a thing, he asks, can be affected by odour and yet not smell it, what is there in smelling odour other than just being affected by it? And he answers that smelling happens when a thing is affected by odour in such a way as to perceive it. But air is not affected in this way, since it has no sensitive potency; it is affected only so as to become a sense-object, inasmuch as it affords a medium for sensation.