SOCRATES: Consider a further point: did we not understand them to explain the generation of heat, whiteness, or anything else, in some such manner as the following:—were they not saying that each of them is moving between the agent and the patient, together with a perception, and that the patient ceases to be a perceiving power and becomes a percipient, and the agent a quale instead of a quality? I suspect that quality may appear a strange and uncouth term to you, and that you do not understand the abstract expression. Then I will take concrete instances: I mean to say that the producing power or agent becomes neither heat nor whiteness but hot and white, and the like of other things. For I must repeat what I said before, that neither the agent nor patient have any absolute existence, but when they come together and generate sensations and their objects, the one becomes a thing of a certain quality, and the other a percipient.”
Socrates characterizes the source of perception—“the quality”—as the agent and the “perceiving power” in the subject as the patient. Hence, these are relative terms in the same way that “interior” only makes sense relative to “exterior.” But to identify this relativity in perception is not the same thing as affirming ontological relativism or intromission or materialism. I think the important thing is not to get hung up on the terminology but to try to see how what he’s saying can be right. Also, three things are worth noting in tangent to the argument: first, Plato invented the word for “quality” in Greek (ποιότης), which Senecca translated into the familiar Latin qualitas. Second, the relevant discussion in the Theatetus dialogue strikes me as the likely source of the heart of the dynamis-energeia (potentiality-actuality) distinction at the heart of Aristotle’s physics and metaphysics. Third, I believe that the specific doctrines that Plato advances are often the least important elements of his dialogues and that many interpreters mistake the container for the contents.
SOCRATES: “Apply this to sense:—When the eye and the appropriate object meet together and give birth to whiteness and the sensation connatural with it, which could not have been given by either of them going elsewhere, then, while the sight is flowing from the eye, whiteness proceeds from the object which combines in producing the colour; and so the eye is fulfilled with sight, and really sees, and becomes, not sight, but a seeing eye; and the object which combined to form the colour is fulfilled with whiteness, and becomes not whiteness but a white thing, whether wood or stone or whatever the object may be which happens to be coloured white. And this is true of all sensible objects, hard, warm, and the like, which are similarly to be regarded, as I was saying before, not as having any absolute existence, but as being all of them of whatever kind generated by motion in their intercourse with one another; for of the agent and patient, as existing in separation, no trustworthy conception, as they say, can be formed, for the agent has no existence until united with the patient, and the patient has no existence until united with the agent; and that which by uniting with something becomes an agent, by meeting with some other thing is converted into a patient.
The above passage is a famous Platonic description of the extramission theory of vision, in which light proceeds from the eye and not only into it. Many people will believe that vision is “settled-science” and Plato was just wrong. But the boot is almost certainly on the other leg and the person who says something like this betrays a lack of understanding in respect to science and philosophy alike. In the first instance, “settled science” is a contradiction in terms because science is a process and the nature of a process is not to be “settled.” Moreover, the engine of scientific progress is precisely the dialectical tension that derives from opposition to what has ostensibly been “settled.” I was not around when Einstein published his “Field Equations” in 1905 but he almost certainly had to tolerate a lot of tedious detractors with their claims of “settled Newtonian science.” Extrapolate the same pattern to all scientific advancement. The person who rejects the extramission theory of vision on the grounds of the above objection also betrays a deficient understanding of philosophy, as I indicated. That being said, philosophy is more difficult to understand than science so this objection warrants more tolerance.
I think a fundamental source of confusion for many modern people is the manner in which scientific thinking has conditioned us to think of light as a physical force or substance or particle, on the one hand, and to pretend that we do not exist, on the other. Reification and nihilism: the two horns of Ahriman, as it were. The metaphors of the physicists serve to inform their own conceptions in ways they probably do not understand. In any case, the view that light must be a physical substance is not self-evident and neither, therefore, is the fact that physicists are talking about the same phenomenon as Plato. The scientific view replaced the Platonic understanding of light as that which makes the world actually manifest as opposed to only potentially so. Hence, light itself is invisible and yet it is the condition of visibility as such. We imagine to see light but this is largely due to our opiated faith in the abstractions of materialism and the tendency of this way of thinking to atrophy our organs of attention. Phenomenologically, we only ever see colours. Of course, light is that by which we see those colours. Gregory of Nyssa is famous for his distinction of the essence and the energies of God. I think this is a helpful analogy to understand the relation of light and colour.
It can be demonstrated that the interior of the eye is illuminated in favorable external conditions and that this illumination serves to stimulate various nerves in the retinae, optic nerves, and visual cortices, etc. But nothing in this picture establishes that these physical and physiological phenomena have anything to do with vision other than the fact that if they are damaged or altered, that a correlative effect in vision is ordinarily observed. But it begs the very question that is at issue to imply that this correlation proves the intromission theory because the effect may just as well be the result of having tampered with the physical organs of extramission.
As indicated above, a traditionally philosophical view of light sees it not as a wave or a particle, or anything else, but as the condition of visibility. It is on the threshold between the latent and the manifest, the potential and the actual. Hence, as Aristotle says, light makes potential colours into actual ones. This was also Goethe’s view and behind his polemics against Newton and the Newtonian theory of optics. From this perspective, it is self-evident that extramission is correct and no verification through scientific instruments is necessary to prove this. Instead, the proof is contained in the experience of vision and intelligibility. The fact that we can make sense of external events implies that, whatever else is happening, vision is extending beyond the physical organs of vision. Otherwise I would be trying to make sense of phenomena that did not contain their own cause since they would be mere internal representations of real phenomena. Ultimately, any argument against extramission tacitly affirms it because if intromission alone were correct, then each of us could only dispute his own private representations. What does it mean that this often seems to be the case? I don’t think it disproves extramission because if only intromission were true, it would be impossible to notice.
All of this being said, while complementing intromission theory of vision (i.e. light enters the eyes) with the extramission one (i.e. light proceeds from the eyes) is much closer to the truth than the former theory alone, I think the basic dichotomy is fundamentally inadequate to the phenomenon we are attempting to grasp. If we are attempting to describe the physics and physiology of the eye, then perhaps intromission alone is satisfactory. But then we should not pretend to be addressing the question of vision at all. After all, we don’t see with our eyes but through them. Any adequate treatment of vision would have to include the soul together with its interface with its material instruments and the soul is not essentially spatial at all. Hence it is not right to think of something “going out” or “coming in” unless these terms are understood non-spatially.
In other words, the obstacles to understanding the nature of sight lie far deeper than the intromission theory of perception alone. I think it stems rather from the entire materialistic paradigm inaugurated by the likes of Bacon and Galileo. From this paradigm follows the impulse to conceptualise everything according to what it is made of rather than what it is. Thence follows the theory that light must be a physical substance because physical substances are the only things that exist. Obviously, if (1) light is a physical substance and (2) it is entering our eyes in the act of perception and (3) this is the only thing that is happening, ergo there is no way that we are in contact with true being through perception. The unelectable consequence of this view is, therefore, the representational theory of perception, in which we create imaginary representations of true being in our own minds without ever achieving direct contact with the former at all.
One brief note in respect to conceptualizing things according to what they are made of rather than what they are (i.e. material cause versus formal cause) as the hallmark of modern scientific thought: some people have attempted to identify Plato’s view as proto-scientific. While there is some truth to this, it is precisely the most conspicuous blind spots among scientists today that Plato devoted much of his career to refuting. Compare, for instance, this delightful parody of Baconian science and materialism per se, from Plato’s Phaedo:
SOCRATES: “I might compare him to a person who began by maintaining generally that mind is the cause of the actions of Socrates, but who, when he endeavoured to explain the causes of my several actions in detail, went on to show that I sit here because my body is made up of bones and muscles; and the bones, as he would say, are hard and have joints which divide them, and the muscles are elastic, and they cover the bones, which have also a covering or environment of flesh and skin which contains them; and as the bones are lifted at their joints by the contraction or relaxation of the muscles, I am able to bend my limbs, and this is why I am sitting here in a curved posture—that is what he would say, and he would have a similar explanation of my talking to you, which he would attribute to sound, and air, and hearing, and he would assign ten thousand other causes of the same sort, forgetting to mention the true cause, which is, that the Athenians have thought fit to condemn me, and accordingly I have thought it better and more right to remain here and undergo my sentence; for I am inclined to think that these muscles and bones of mine would have gone off long ago to Megara or Boeotia—by the dog they would, if they had been moved only by their own idea of what was best, and if I had not chosen the better and nobler part, instead of playing truant and running away, of enduring any punishment which the state inflicts. There is surely a strange confusion of causes and conditions in all this. It may be said, indeed, that without bones and muscles and the other parts of the body I cannot execute my purposes. But to say that I do as I do because of them, and that this is the way in which mind acts, and not from the choice of the best, is a very careless and idle mode of speaking. I wonder that they cannot distinguish the cause from the condition, which the many, feeling about in the dark, are always mistaking and misnaming.”
The argument from the Meno is helpful to juxtapose against the one from the Theaetetus because they might initially appear to be at odds with one another. In the first instance, Socrates seems intent to demonstrate the possibility for objective intellection of ideas while in the second, he seems to be advancing a form of relativism or “correlationism.” Self-evidently, “it is impossible for the same thing to belong and not to belong at the same time to the same thing and in the same respect” and hence Plato might appear to contradict himself. I don’t think this is the case but I also don’t think it is very important. Perhaps this will surprise the reader but I think it will be agreed that Plato, taken as a whole, appears less interested in establishing a set of doctrines than in perfecting the soul. This could be seen as elevating the soul—lending her wings, as it were (to borrow the image from the Phaedrus), to behold the truth directly rather than through discursive mediation. I have also begun to regard Plato’s dialogues as templates for how to carry out a dialogue that is oriented towards the truth and not something ulterior, which will be the de facto orientation of most dialogues lacking any sort of intervention. I think many people fail to recognize that the ability to carry out a productive conversation concerning an issue over which the interlocutors do not initially agree is not something that any of us is born knowing how to do but instead it is the result of education (to be differentiated from STEM or vocational training). Hence Plato’s dialogues serve as pillars of Western civilization but not for the reason many people at first suppose. There is, of course, much more to be said on this theme but suffice it here to say I think most people read Plato in a manner that is perhaps adequate to Aristotle but not to his master.
The reason I do not think the doctrines entertained in the Theatetus dialogue stand in contradiction to the more traditional Platonic view is that the subject of the Theaetetus is sensory perception and Plato never intends to advance the latter as the foundation of knowledge to begin with. I think he’s right about this insofar as sense perception is neither true nor false. That the sun appears greater on the horizon than at midheaven is not “incorrect” until I infer that the sun is changing sizes. The sensory phenomena is just what it is and maintains a perfect correspondence with the laws of optics and visual perception. “Subjective” and “objective” are terms that carry so many different connotations as to render them almost meaningless but I think that impartial consideration reveals that, if anything, the subjective element of perception is lent by the senses and the objective element by the noûs or intellect. Your visual experience of the sun is totally opaque to me while the fact that it is the sun and that it might be conscious (this is something that I think deserves further discussion because as it stands, I think it is actually wrong but potentially correct) are thoughts that we share in through participation in their objective semantic essence. Of course, the majority of well-known philosophers since Bacon and Locke would reject this but they have been wrong about other things so it should hardly come as a surprise that they were confused about the nature of perception.