Sense and Science: An Aristotelian Perspective

Introduction

In sensation the “that out there” is perceived and becomes a “this in me”, wherein the “this in me” is only perceived because it remains the “that out there”. Through sensation, an animal apprehends the world outside and desires particular external things. It is through sensation that a dog can apprehend food and a man can apprehend a symphony. This is the most noble of the powers in matter and the most self-determinate of the naturally determined; of all enmattered acts, the sensitive soul is the most actual. With respect to its object, the science of sensing things is the highest of the physical sciences.

This thesis is a drawing together of what others have done in biology in order to present a more complete picture of sensation. In particular, the two main sources of knowledge of any material thing are common experience and experiments. Unfortunately, a significant number of conclusions gleaned from common experience is largely and unduly abandoned; one of these conclusions is that the sense organ must hold itself at the mean between the sensible extremes. In this thesis I will address the extent to which common experience elucidates material causes by example by presenting Aristotle’s demonstration that the sense organ must hold itself at the mean between the sensible extremes, and then draw from neuroscience to show what this mean looks more concretely.

This will consist of three parts. The first section deals with sensation formally from common experience; the second deals with sensation materially from common experience; and the third section deals with sensation generally in light of more recent discoveries from experiments.

Aristotle's Formal Account of Sensation from Common Experience

Concerning sensation, Aristotle begins with a general treatment on the passivity of sensation, and then proceeds to a general treatment of the objects of sensation, starting with what seems to be the most noble and ending with what seems to be the most fundamental of the senses. After dealing with the objects, he comes back to the topic of external sensation in general, making more precise claims about how the organs are receptive of the sensible species.

First, Aristotle defines sensation generally as a reception. This conclusion is presented as a response to Empedocles, who claimed that the sense organ must have the qualities that it senses, because like knows like, and because the sense organs must be a mixture of the sensible qualities hot, wet, cold and dry. This position has two difficulties however. First, if it were so, the sense organ would not only sense external objects but also itself. Second, the sense organ would sense in the absence of an external object. It already has everything that the objects have to give it after all, so why would it depend on them for sensation?

It is not difficult to see that in fact the senses do not sense their own organ. If a man puts is hand into a bucket of 30-degree saltwater, for instance, he feels a temperature that is much colder than the temperature of his hand. In fact, the water starts to feel warmer as his hand becomes colder. It is true that the hand has a temperature, but it senses the temperature of its surroundings, not the temperature that it has in itself. That sensation does not happen in the absence of an external object is not difficult to manifest either, for take away all sounds, and nothing is heard; take away all colors, and nothing is seen.

​It may be asked why there is no sensation of the senses themselves; and why they do not produce sensation without something… [external], seeing that they contain within themselves fire and earth and other elements that give rise to sensation, either of themselves or through their accidental qualities. It becomes evident that the sensitive power is not an actuality, but is only potential; which explains why it does not sense [without an exterior object] as the combustible does not burn of itself without something to make it burn.[i]

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No opinion can be appropriately dismissed with a complete degree of satisfaction unless it is first seen why it was held, nor does Aristotle dismiss Empedocles without explaining why one would think that like knows like. If sensation is a reception, it is a reception of a sensible quality, but any form is a principle of making something like itself, so the sensible qualities must make the sense organs like themselves. When it is not sensing, the organ is unlike the sensible qualities, and this allows the sensible qualities to be received, but the reception of the sensible qualities does make the organ more like what is being sensed, and this is what causes sensation.

All things are moved and affected by an agent, or something in act. Hence it is, that a thing is affected both by its similar and also by its dissimilar, as we have said. What is being affected is dissimilar: what has been affected is similar.[ii]

In a way Empedocles was right, and in a way he was not right.

After proving that sensation is a reception, Aristotle turns to the question of in what manner it is a reception. Although generally sensation is more known to us than knowing, here Aristotle aptly uses knowing to describe sensing, for the various levels of act and potency are more apparent in the intellect than in the senses. There are several ways in which people are called knowers: It is one thing to say that a man is a knower in virtue of having an intellect; it is quite another to call a geometer a knower, and still another to call Euclid a knower while he is contemplating the truths of which he already had the knowledge. Take a random Joe off the street, and he will not yet be able to contemplate Euclid I-32; his intelligence is indeed a prerequisite, but it must be supplemented by a discursive process of learning. Through this learning, Joe is made more perfect by coming to knowledge and can contemplate the equality of the interior angles of all triangles. The man with knowledge of the interior angles of the triangles is in act relative to the man with only the natural capacity to know, but he is in potency relative to the man who is actually thinking about the interior angles of a triangle. A distinction between kinds of act and between kinds of potency thus follows. The man who knows proposition 32 is in potency to thinking about it, and the man who has the intellectual faculty is also in potency to it, but not in the same way. One is remotely in potency; the other proximately.

From this flows the distinction in act. One act is being, and the other is doing; but being is in potency to doing, for which reason specific kinds of being are called nature in the primary sense of the term. The intellectual faculty is hardly a doing, but it is certainly a being that can do something; it can know and think. Knowledge itself is a kind of being, but one in potency to only what is more doing, namely thinking. This is the difference between actuality and activity.

A distinction between different kinds of alteration flows out of this. In the ordinary sense of the term, alteration is a qualitative motion, and qualitative motions require that one quality be lost and another gained. Although there is something like a qualitative coming to be in gaining knowledge, or in going from a passive knowing to an active thinking, these do not involve a destruction of a contrary quality: Ignorance may be lost when a man learns, but ignorance is a privation, not a contrary. Hence, coming to know may be called an alteration, but only in a extended sense. Whereas alteration in the ordinary sense (a change in temperature, for instance) involves the destruction of a contrary, coming to knowledge perfects and maintains what is in potency to it. In brief, the two sorts of act are being and doing; the two sorts of potency are a proximate potency and a remote potency; the two sorts of alteration are by destroying a contrary and by maintaining the potential.
Therefore the first two are knowing in potency. But one has undergone a change through being taught, and is often altered from the contrary state, whereas the other is moved to action from simply having sense or grammar without acting [accordingly]; but in a different way from formerly when he had not yet acquired any habit [of knowing].

​Nor is ‘being acted on’ a simple term. It is one thing to be somehow destroyed by a contrary; quite another when what is in potency is maintained by what is in act, and is of a similar nature, being related to the latter as potency to act.
For when a man possessed of knowledge becomes actually thinking, there is certainly either no ‘alteration’ – there being a new perfection in him, and an increase of actuality; - or it is some novel kind of alteration. Hence it is a misleading statement to say that a man is ‘altered’ when he thinks, as to say this of the builder when he builds. The process from being in potency to understand and think to actually doing so should not be called instruction, but has by rights some other name.[iii]

Having used the intellect to make this distinction in potency, act and alteration clear, Aristotle then applies it to the senses, and this he does it very briefly. “The first change in the sensitive being is caused by the parent. When it is born it is already endowed as with knowledge. Actual sensation corresponds to the act of thinking.”[iv] This is an analogy. Birth is to the act of sensing as learning is to the act of contemplation. Just as birth gives a first act that is a proximate potency, so learning gives a first act that is a proximate potency, and just as going from knowing to thinking is an alteration only loosely, so too with going from being sensitive to sensing. For everything necessary to sense on the part of the subject is received at birth, and the organ of sense then received is perfected and maintained by sensing. Sensation is a change from not-doing to doing, not a change from not-being to being.

After these and a few more general remarks on sensation and its relation to its object, Aristotle discusses the five senses. In each of these five senses, Aristotle finds contrary sensible qualities. In color, for instance, there are white and black; in sound, high and low; in odor and flavor, the sweet and the bitter; in the tangible, the hot and cold, & the wet and dry.

The formal definition of sensation can then be given. Sensation is the reception of contrary qualities in external objects, received in a sense organ in such a way that the received qualities do not destroy any natural quality of the organ by their reception. Or, sensation is a reception of sensible qualities that gives rise not to a different state of being so much as to a kind of doing.  

This having been established, Aristotle then claims that sensation must be the reception of form without the matter, as a signet ring impresses its form on wax, and the shape of the ring is received without respect to whether the ring was copper or brass. This is a particularly puzzling analogy, for whereas one might think that Aristotle would say that the matter of the sense organ is not altered by this immaterial reception, he says instead that the matter of the sensed object is not received. This hardly looks like a unique kind of reception, for when something becomes hot, it does not become hot by gaining whatever the matter of the heating agent happens to be, but simply by receiving the form of the agent without the matter. Similarly, when air becomes light, it does not become light by becoming receiving sun-matter, but by receiving a form from the sun without the matter of the sun.

Thankfully, St. Thomas addresses this point of confusion. After pointing out that, while it is true that anything that undergoes anything does so in virtue of the form of an agent, and not its matter, this undergoing can happen in different modes. Specifically, sometimes the form is received in the same mode in which it exists in the agent, and sometimes it is received in a different mode. In sensation, the form must be received not in a material mode but in a formal mode. If this were not true, sensation would be the first of the two kinds of act described above, rather than the second. Thomas Aquinas says of this:

Et ponitur conveniens exemplum de sigillo et cera. Non enim eadem dispositio est cerae ad imaginem, quae erat in ferro et auro. Et ideo subjungit, quod cera accipit signum idest imaginem sive figuram auream aut aeneam, sed non inquantum est aurum aut aes. Assimilatur enim cera aureo sigillo quantum ad imaginem, sed not quantum ad dispositionem auri. Et similiter sensus patitur a sensibili habente colorem aut humorem, idest saporem aut sonum, sed non inquantum unumquodque illorum dicitur, idest non patitur a lapide colorato inquantum lapis, neque a melle dulci inquantum mel: quia in sensu non fit similis dispositio ad formam quae est in subjectis illis, sed patitur ab eis inquantum hujusmodi, vel inquantum coloratum, vel saporosum, vel secundum rationem, idest secundum formam. Assimilatur enim sensus sensibili secundum formam, sed non secundum dispositionem materiae.[v]

From these considerations the general conclusion arises that sensation is semi-immaterial. Sensation itself cannot be a material reception because it is a perfection and a kind of doing. It cannot be wholly immaterial however, because it is of particulars. To know “white” without matter altogether is to know what it is to be white. Because sensation is a reception of particular forms in a material organ, the power is not fully understood until it is known how the matter is disposed to receive the form.

Aristotle's Material Account of Sensation from Common Experience

Aristotle holds that the sensible forms are contraries, while the sensitive forms are means, or proportions, between those contraries. It is by this that he intends to explain how the organ can accomplish its end. For this conclusion, Aristotle offers two arguments, one exclusively for touch and the other also for the rest of the five external senses, and he shows that the mean is a cause of several other properties of sensitive animals. The first argument, concerning touch, proceeds from the premise that the tangible contrarieties could not be received unless the organ held itself at the mean; and after this argument he shows how the conclusion explains how the sense discriminates between the contraries. The second, more universal argument concerning all the senses is from the premise that the external senses are destroyed by extremes. This implies they must exist in a proportion, which explains sensitive pleasure between harmonies and proportions.

The first of these arguments is given in chapter 11 of book 2:

Tangible objects vary therefore with differences of body as such – I mean the differences by which the elements are distinguished as hot and cold, wet and dry, as is stated in our work on the elements. The sense organ for these, the tactile, in which the sense called touch is principally lodged, is the part in potency to these qualities. For to perceive is to receive an impression. Hence whatever makes the organ to be such as itself is actually, does so, the organ being in potency thereto. Hence we do not perceive what has heat, or cold or hardness or softness to an exact similitude of our own heat, and so forth, but rather the extremes of these: the sense being, as it were, in a mean state between the contrary extremes in the objects perceived; which is how it discriminates between them. For a mean is discriminative; in the presence of either extreme it becomes the contrary one.[vi]

According to the ancient cosmology, every sublunar body is composed of four elements, each of which has two of four elemental contraries, and all material forms are derived from proportions of these four contraries. The organ of touch must be receptive of all four; yet, since nothing can receive what it already has, one must wonder how the organ can receive any of them. The evident solution is to observe that the organ of touch is not exempt from the requirement of all material things that they partake in these two contrarieties, but still there can be variations in degree. It follows that the sense organ must have temperature, wetness, and dryness, like the sensible objects, but the organ can still be receptive by having any of these contraries in a different degree from its object.  That two things are both hot does not mean that they have the same temperature, for which reason one of two hot things is able to receive heat from the other. If the sense object had the contraries to the same degree as the organ, the organ could not receive the form of the object and no sensation would occur, as all sensation is a reception. When an elemental quality is received by the organ, it can be apprehended by the contrast between it and the quality present materially in the organ.

As presented by Aristotle, this argument depends on the theory of the four elements, but a similar argument can be given without this debunked theory. Every body must have some temperature, but the organ of touch is receptive of contrary temperatures; therefore the organ of touch must have a mean temperature.
From this, Aristotle further shows how the sense distinguishes between hot and cold. In general, distinguishing requires that two things be present in act, for something cannot be distinguished from nothing. The organ of touch can apprehend cold as one side of a contrary because the organ is the other side of the contrary relative to the object perceived.

This latter argument could just as well be presented in the reverse order. Hot and cold are sensed as contraries. To sense these as contraries is to distinguish them in an organ, and distinguishing requires that two things be present to be compared. When one hand feels only cold, the coldness is felt as a contrary to heat, whence there must be some mean in the organ that becomes heat in the presence of cold. This argument applies equally to every sensible contrariety.

Aristotle’s second argument is presented in Chapter 2 of Book 3:

Now if voice is a harmony of some sort, and voice and hearing of it are somehow one, and also somehow not one and the same; then hearing must be a kind of proportion. For this reason anything excessively shrill or deep destroys the hearing; and the same in flavors destroys the taste; and in colors, the sight, whether the excessively brilliant or the dark; and in the smell, a strong odor, whether sweet or bitter; as if the sense were a certain proportion. Hence too, those [savors] become delectable which, from having been pure and unmixed (e.g., the bitter or saline) are brought into a proportion. Then indeed they give pleasure. And in general what is compounded is more of a harmony than the sharp or low [sounds] alone; or in the case of touch, what can be both heated and chilled. Sense is a ‘proportion’ which is hurt or destroyed by extremes.[vii]

Sensible species are the same whether in the organ or in the object. Hence, if voice is a proportion, the hearing of a voice is also a proportion. That we delight in harmony is also a sign that something in the faculty of sensing – presumably the organ – is itself a kind of proportion. And further, that we cannot hear especially high or low tones implies that the organ is in some way a mean. Similar instances can be found in other senses. Whether it is sight, sound, taste, or smell, whenever something is sensed that is too sensible, the sense is hurt or destroyed. This means that in some way or another, receiving the sense-object tends to move the organ out of its natural state. Still further, when two contrary objects move the same thing out of its natural state, this natural state must be the mean between them. This explains why sensing a proportion is pleasurable. For if the senses are a kind of proportion between their contrary objects, a sensation of those contrary objects together in due proportion will give pleasure, for like delights in like.

Someone might wonder whether these two arguments really are talking about the same kind of thing. A proportion does not seem to be a mean, after all, since a mean involves contraries that are mixed whereas a proportion relies on their being distinct and unmixed. This confusion arises from relying too heavily on the meanings of the terms in the De Anima divorced from the properties that they explain and the science of which it deals. The passivity is the same, and both arguments explain the passivity of sensation. Besides, the word “proportion”, when applied to natural science, does not signify an equality of two ratios of quantities so much as a fittingness between the mixture of contraries in a single natural object. It is not as though the organ of touch is receptive by being in the mean while the other organs are receptive by being proportions, but both are means and proportions together; every sense distinguishes between contraries after all, and Aristotle does say in the above passage that “in general what is compounded is more of a harmony than the sharp or low [sounds] alone; or in the case of touch, what can be both heated and chilled”. In any sense organ, the sensible contraries come together in a due proportion to make a mean. Through this mean, they distinguish between their contraries; on account of this mean, they are destroyed by an overly powerful contrary; because of this mean, they feel pleasure in the presence of moderate or harmonious contraries. It is true that the argument about the elemental contrarieties would apply only to touch, as it is not clear that every body must have color or sound, but the other arguments apply in common. Just as the sense of touch distinguishes between hot and cold, so the sense of hearing distinguishes between high and low. Just as everything seems dim after the eyes grow accustomed to an excessively bright light, so everything feels hot when a hand has become cold. Just as the sense of taste delights in a mixture of different flavors, so the sense of touch delights in moderate temperatures. Hence, instead of saying that Aristotle deals with the sense of touch separately from the other senses on account of a different sort of material composition in relation to the objects, it ought to be held that he proceeds in the order of the more clear to the less clear. He deals first with touch, and later with the other senses, because it is more clear that the sense that is receptive of elementary qualities must hold itself at a mean, and it is only in touch that he has any precise idea of what he thinks this mean must be.

It is also curious that an organ can be said to necessarily be potentially white if it can never be materially white while remaining an organ sensitive of white. It seems as if we were saying that a sense organ is potentially what it cannot be: a most abhorrent proposition. The last argument above offers some clarity on this point, because while it is true that the activity of sensing is not material, it nevertheless is necessarily accompanied by a tending toward material change. The notion of a mean that is sometimes tending toward an extreme without ever being able to reach that extreme is also not far from every-day experience. When a car gets stuck in the snow and several people get out to push the car, it will inevitably be the case that some people will look like they are pushing while others actually will be pushing. When the car is pushed onto the pavement once more (or onto the kitty-litter, as the case may be), the bums can be told apart from the pushers by the fact that the pushers will fall down while the bums will still stand, appearing to be pushing the frigid air. This is because while the bums and the pushers alike were moving at little or no speed while the car was being pushed, the pushers alone had an impulse to move forwards. This impulse was impeded by a weighty car, and when the car was removed, they moved. Something similar seems to be the case in the sense-organ, for here a sensible form inheres in matter without changing the quality of the matter, and here the soul keeps the organ at a certain quality just as the weight of the car kept the pushers in a certain place.

In sensation, an actively sensing organ is thus like a man pushing a car, and a sensitive organ that is not sensing is like a man standing behind it without pushing. In either case, just as the soul keeps the organ from moving out of its proper proportion, so the car keeps the men from moving forwards. Aristotle seems to be thinking of something like this, for just as too much of a sensible quality would move an organ out of its mean, so a sufficient amount of forward impulse would make a pusher move forwards. Even when not potent enough to move the man forwards, however, the impulse to move forwards is present in him.

This adds more clarity to the conclusion that has already been reached, that sensation is in a way material and in a way immaterial. It had already been apparent that apprehension of something as outside cannot itself be a material change; nevertheless, so long as it is of a particular, it must occur in a material organ. Now, it is also clear that this immaterial apprehension must be accompanied by some impulse in the matter, for when exposed to a potent sensible quality it does change. Furthermore, the external senses are sensible by the common sense, and this is only possible if there is a material component to the act of sensing. If only the immaterial component of the act of external sensation were sensed by the common sense, the common sense would not be sensing at all; it would be knowing. This is clearly not the case however, for when we see that we are seeing, we are not apprehending “what it is to see” but are apprehending one particular act of seeing.

As might be expected from the fact that the mean between the sensitive extremes explains the degree to which sensation is material, this mean is a part of the essence of the sensitive animal. This is clearly implied by Aristotle, who not only teaches that the organ must hold itself at a mean, but also considers this mean as a per se cause of the sensitive power. There are two main ways of discerning whether something is a per se cause: first, by seeing that a cause pertains to this species and to no other; second, by seeing that the cause explains the properties of the species in question. Aristotle provides what amounts to an example of each right after the renowned signet-ring analogy:

​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 is lost, which is the sense. It is as with tones 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 on materially.[viii]

And again:

That the impassibility of the sensitive faculty is not like that of the intellective faculty, is evident from the organs and from sensation itself. For the sense cannot receive an impression from too violent a sense-object – e.g., a sound from very great sounds, whilst from over-powerful odors there comes no smell, nor from over-strong color any seeing. But when the intellect understands something highly intelligible, it does not understand what is inferior to these less than before, but more so., For whereas the sensitive faculty is not found apart from the body, the intellect is separate.[ix]

It is clear from these passages that Aristotle thinks that both criteria are met in the case of the mean state as the natural form of an organ of sensation, and for this reason, he thought that having an organ at the mean between the sensible extremes was the material cause of the sense power in animals.
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The mean between the sensible extremes is a per se cause of the sensitive power, and as such it belongs in the true definition of the sensitive animal. This true definition (as differing from a syllogism in grammatical form) can now, accordingly, be made clear:
Minor premise: A sensitive animal has the soul capable of sensation.
Major Premise: Everything with a soul capable of sensation must have organs that hold themselves at the mean between the sensitive extremes.
Conclusion: A sensitive animal must have organs that hold themselves at the mean between the sensible extremes. [x]

Accordingly, a sensitive animal is one which has a soul capable of sensation and organs that hold themselves at the mean between the sensible extremes. Or to put it about as distinctly as common experience allows, we may say that a sensitive animal is one that has organs that hold themselves at the mean between sensible extremes, these being tools of a semi-immaterial power of reception of those contraries, which reception does not cause the power or the organ to lose a contrary quality but perfects and preserves them, through the reception’s being an apprehension of the object of the power, for the sake of which the mean exists.

An Initial Examination of Aristotle's Account of Sensation In Light of Experimental Discoveries

What remains is to add concretion to the conclusion arrived at: So the sense organ must hold itself at the mean. What is this mean? Where is this mean? How does this mean sustain itself? Is the mean constituted similarly in all of the senses or in an altogether different manner? Can we understand better what physics and chemistry underlie this mean in light of what more modern science has taught us?

A first attempt at showing what the mean looks like concretely can be given by observing the fact that any sense organ holds itself a sort of equilibrium. Sensation happens when the organ is moved out of that equilibrium and wants to move back. The ear’s cochlea for instance is a membrane that vibrates together with the sounds in the air, and the parts of the cochlea will move further away from their resting place when the sound is louder, as if the cochlea were a mean with respect to tension and position. This would account for why hearing is hurt by excessively loud sounds, as if the cochlea were a string that was too violently struck and either was forced out of tune or broke completely. Different parts of the cochlea, however, will vibrate with different frequencies. It would be somewhat strange if the differences in tone were apprehended simply by the different parts of the cochlea, for it is not clear that the cochlea in any way becomes one contrary in the presence of another.

In attempting to say concretely where discrimination between contraries occurs, a host of difficulties arise. It would be reasonable to expect some mean to exist in the eye, by contrast to which yellow can be sensed as different from green, but the modern understanding of the retina seems to contradict this. Instead of one receiving mean in the eye, we find three types of cones, each of which is most receptive of a mean frequency of light, and the difference between colors is determined by the numerical ratio of the stimulated cones proportioned to different colors. One cone cannot be the Aristotelian mean, for the cones do not distinguish between different frequencies but only say how likely it is that the light matches the color that they are best at seeing. In touch, we might expect to see some nerve endings that are receptive both of hot and of cold and distinguish the two by being at a mean temperature, but instead we find some nerve endings that are stimulated by heat (or capsaicin, interestingly) and others that are stimulated by cold (and menthol, by the way). If there is some mean by which these senses discriminate, it cannot be totally found in the nerve endings, nor in the individual cones and rods of the retina. In fact, every sense organ can be broken up into smaller parts, each of which is only receptive of one or another contrary, or some middle state within the contrariety. The ear, for instance, has several thousand hairs distributed across the cochlea. Any one tone will only cause a part of the cochlea to vibrate, which then moves a small number of hairs, and these in turn create electrical impulses that are sent along the auditory nerve. There is a sort of mean in the cochlea with respect to tension and position, but this could hardly account for the discrimination between tones, as any part of the cochlea can only receive one tone, and what can receive only one thing can in no way discriminate. Where then is the mean? It is clear from common experience that we discriminate between sensible contraries, and Aristotle aptly deduced that this must be on account of some organ that is receptive of both sides of the contrariety in different ways, but no cone or rod in the retina and no nerve ending in the flesh, no hair cell on the cochlea can constitute such a mean.

Another difficulty must be acknowledged before moving forwards. Common experience is sufficient for saying that there must be some mean that is receptive of contraries and becomes one in the presence of the other, but it does not say precisely this mean’s material constitution would be. This is because sense organs do not receive the object directly, but only mediately, and the sensible species need not be materially the same in the object and in the medium. In a visible object, for instance, the species is color; in light, the act of the medium, the species is an ethereal wavelength. There is an equivocation when we call a fire-truck red and when we call a light red.[xi] Nothing is philosophically problematic with positing internal media either, as Aristotle realized that this is the function of the flesh in the sense of touch. Could there be internal media in the other senses as well? How would one tell the difference between the medium and the organ with the apprehensive power? What would the material counterpart to the sensible species be in such a medium?

​It is tempting to dismiss this line of questioning by saying that common experience shows that sight is in the eye, hearing in the ear, taste in the tongue, etc., but aside from being a dubious claim on its face[xii] – if someone were to take this vague allusion to common experience as a proof that sight is in the retina, touch in the nerve endings, hearing in the inner ear, etc – it is utterly at odds with the discoveries of Michael Merzinich. This remarkable neuroscientist replaced the cochlea with an artifact able to translate different pitches into electrical impulses, hooked it up to auditory nerves that had been attached to severely damaged cochlea, and made the deaf hear.

When the external world produces sound, different frequencies vibrate different little hair cells within the cochlea. There are three thousand such hair cells, which convert the sound into patterns of electrical signals that travel down the auditory nerve into the auditory cortex… Cochlear implants are for those who are deaf because of a profoundly damaged cochlea. The implant replaces the cochlea, transforming speech sounds into bursts of electrical impulses, which it sends to the brain…He worked with communication engineers to design a device that could transmit complex speech on a small number of bandwidth channels and still be intelligible. They developed a highly accurate, multichannel implant that allowed deaf people to hear, and the design became the basis for one of two primary cochlear implant devices available today.[xiii]

Since these cochlear implants are powered by batteries, not nutritive souls, it would be absurd to claim that hearing takes place in them. Nevertheless, hearing does take place by means of them, whence the cochlea and hair-cells they replace together with everything between them and the object must be an auditory medium, not the matter imbued with the power of sensation, rather instruments that move the species closer to the proximate medium of the sense. Not only the air, but also the ear drum, the hammer, the anvil, the stirrup, the oval window, the cochlea, and even the cochleal hair cells must be media of the sense of hearing through which the sensible species travels prior to being sensed.

The organ that senses sound then must be something that comes after the cochlea. What comes after the cochlea? Something that all of the senses have in common: Electricity. Nerves, neurons and electricity. Here, at last, we find a plausible candidate for the location and material constitution of the discriminative mean we’re looking for.

A bit of neuroanatomy will help clarify this further:

​Each neuron has three parts. The dendrites are treelike branches that receive input from other neurons. These dendrites lead into the cell body, which sustains the life of the cell and contains its DNA. Finally, the axon is a living cable of varying lengths (from microscopic lengths in the brain, to some that can run down to the legs and reach up to six feet long). Axons are often compared to wires because they carry electrical impulses at very high speeds (from 2 to 200 miles per hour) toward the dendrites of neighboring neurons.
A neuron can receive two kinds of signals: those that excite it and those that inhibit it. If a neuron receives enough excitatory signals from other neurons, it will fire off its own signal. When it receives enough inhibitory signals, it becomes less likely to fire. Axons don’t quite touch the neighboring dendrites. They are separated by a microscopic space called a synapse. Once the electrical signal gets to the end of the axon, it triggers the release of a chemical messenger, called a neurotransmitter, into the synapse. The chemical messenger floats over to the dendrite of the adjacent neuron, exciting or inhibiting it.[xiv]

Every neuron is able to operate only because it holds itself at a mean state between positive and negative electrical charges by having a proportion in it of positive and negative ions. When a neuron is not sensing, it is because it is at a state of electrical equilibrium with its surroundings. After a neuron receives enough excitatory ions from adjacent axons, it returns itself to equilibrium by sending off a series of electrical pulses at a breakneck speed through its own axon.

The neuron at last is a plausible candidate for the seat of sensation. The sending of an electrical signal through the axon looks very much like it is simply a transmission, but the receiving of excitatory and inhibitory electrical signals could be exactly that process by which sensible contraries are compared. The distinction of contraries would look very close to how we expected it to, with a tending toward some contrary state by something that naturally holds itself at a mean state. The car analogy could be used to explain this as well, although the equilibrium in a neuron may look more like a bungie cord than a car stuck in the snow.

The sensible species in this case would exist in electricity as in its proximate matter. So saying gives more meaning to several previous conclusions. There is an immaterial and a material component to sensing. The immaterial part has to do with an apprehension, but this apprehension arises from a tendency to move back toward a mean state when the organ was moved out of it. The discriminative mean is materially an electrical mean, and the organ by which we discriminate even between contrary temperatures seems to be the brain. It is true that the external organs are materially altered and are sensible by the common sense on account of their material alteration; this material alteration is electrical, and the objects of all of the interior senses are species existing in electricity as their proximate matter.

Conclusion

​The philosophy of nature seeks to know what natural things are, not in a confused manner, but in their proper concretion. The unity of that end is not broken by the diversity of means employed. On the contrary, it is the same end that governs them, provided that they enable us better to know.[xv]

No two truths can be contradictory. It would be foolhardy to dismiss either what knowledge is gained from common experience or what knowledge is gained from experiments. Only common experience is needed to prove the existence of God or the immateriality of the rational soul, and only common experience is needed to know material causality in a certain, albeit vague manner. As Charles De Koninck put it, “It is not hard to speak with certainty as long as one remains in the common and does not wish to say much.”[xvi] Experiments are necessary to know natural things with a satisfactory level of concretion however. This thesis is in large part intended as an example of this fact. Experimental science may be empty without natural philosophy, but natural philosophy is rather shallow without experimental science.

Neuroscience tells us that these things called neurons send signals to each other in the brain, and this signal-sending is necessary for daily life, but it does not say what this signal sending is, or whether sensation is a motion, a material reception or an immaterial reception, nor does it distinguish sensing from knowing. Natural philosophy on the other hand says that sensation is a reception that is more immaterial than the way plants receive forms, but less immaterial than the way the intellect receives forms, that it is fundamentally of contrary qualities, and that its organ is held at a mean, but it fails to say in respect to what it is materially a mean or where the whole organ is.

It is not until the common philosophy is taken up alongside experimental science that a material thing can be known with its proper concretion. With the two together, the biologist can say with a smile on his face after a long and arduous journey, that sensation is an immaterial reception, but the organs of the sense are also materially affected; sensation is of contrary qualities, but these are distinguished through contrary electrical charges; the sense organ must hold itself at a mean between the sensible contraries, but it does so only mediately. The several exterior senses are of formally different contrarieties, but they are distinguished through the same sort of contrariety. It is not until the biologist knows it in this manner that he fully understands sensation.

Notes & Citations

[i] Aristotle. De Anima, 417a9-14 from Commentary on Aristotle’s De Anima. Dumb Ox Books

[ii] Ibid. 417a17-20

[iii] Ibid. 417a30-417b12

[iv] Ibid. 417b16-19

[v] “And a fitting example is set up from a seal and wax. For the disposition of the wax to an image is not the same as [the disposition] of iron and gold [to the same image]. And, for this reason, he adds that wax receives the sign, that is, an image, [which is] a gold shape or a brass shape, but [the wax does] not [receive that shape] insofar as it is gold or brass. For wax is assimilated to the gold seal with respect to the image, but not with respect to the disposition of gold. And similarly, the sense suffers by the sensible object having color or wetness, flavor or sound, but not according to that by which [the sensible objects] are called particular things, [that is, not on account the matter of the objects]. In other words, [the sense] does not suffer from a colored stone as a stone, nor from a sweet honey as honey: because in sense, [the organ or power] does not gain a similar disposition to the form to [the disposition that] is in those, but it suffers by them insofar as they are of a certain sort, whether on account of being colored, or flavorful, or according to account, that is, according to form. For the sense is assimilated to the sensible according to form, but not according to the disposition of matter.” Thomae Aquinatis, In Aristotelis Librum De Anima Commentarium. Lectio XXIV, 554.

[vi] Aristotle, De Anima 423b27-424a9 from Commentary on Aristotle’s De Anima. Dumb Ox Books

[vii] Ibid. 426a27-b7

[viii] Ibid. 424a28-424b3

[ix] Ibid. 429a29-429b5

[x] See Posterior Analytics, Aristotle, 2.8-10

[xi] In general, a fire truck is called red because it has redness as an inherent, material, and sensible quality, and that quality is the proper object of sight. Light is called red not because it is a sensible quality, but because it makes a sensible quality in the proper object of sight visible. When air is lit up between the eye of the viewer and a fire-truck, the light is called red analogically in virtue of the material quality of the fire-truck. The same material quality does not exist in the light, however, or else the redness would only exist on its surface, and it would be opaque.

[xii] That this claim is untrue when applied to the whole of the exterior sense is already apparent from what has been stated above. The external senses involve a discrimination between contrary objects, and this discrimination must happen in a mean that is receptive of both contraries, but the cochlea, the retina, and the various nerve endings cannot make such a discrimination, for they have no part that is receptive objects. There is reception in nerve endings, and so there might be something of an apprehension there, but that would be a vague sort of apprehension indeed, since it would be incapable of being compared to anything other than a lack of stimulation and a state of equilibrium. If one were to obstinately maintain that the sense of touch must be totally in the hand, he would risk reducing the distinction between hot and cold to one of the common sense. At that point, the question would be less one of how things are in themselves and more one of linguistics.

[xiii] Doidge, Norman. The Brain that Changes Itself, pp 57-58. Penguin.

[xiv] Ibid. pp 53-54

[xv] De Koninck Charles. Are the Experimental Sciences Distinct from Philosophy of Nature, Volume 1 of The Writings of Charles De Koninck, Pg. 449.

[xvi] Ibid. 451

Bibliography:

This paper was initially a thesis written in 2018 under the title Sense and Science in partial fulfillment for my Bachelor's degree at Thomas Aquinas College in Santa Paula, CA. Special thanks to Dr. Sean Collins, my advisor.

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