Richard Sorabji, “Aristotle on Colour, Light, and Imperceptibles,” Bulletin of the Institute of Classical Studies of the University of London 47 (2004): 129-140.
Stable URL: http://www.jstor.org/stable/43646862
Response
I am afraid, as Sorabji here is doing little more than compiling and recounting Aristotle’s statements on the nature of light, color, and sight, that I can do little more, here, than recount Sorabji’s recounting, but we will see what I might extract otherwise, if anything.
“In On Sense Perception 3, a thing’s own colour is said to be a boundary or surface, but not the boundary of the body, rather the boundary of the transparency within the body.” What is this “transparency within the body?
“Where does the borrowed colour of the sea come from? Aristotle points out that with rigid bodies — and he is thinking of opaque ones — the appearance of colour, though not its own colour, can be changed by the surroundings.” This would seem to indicate that color is a property inherent to (rigid) bodies, and is constant. Thus something’s color cannot be changed, only our perception of that color in relation to colors of its surroundings.
Aristotle provides two definitions for light: a functional one, which is clear to Sorabji, and a material definition, which Sorabji considers problematic. Functionally, it is the state in which the transparent can actually be seen through. This seems to indicate that transparency always exists for transparent things, but their transparency is only a potentiality until they are lighted (derived from the perceived opacity of darkness, where the air itself is not any less transparent, but nonetheless cannot be seen through, as though opaque?). The material definition of light, “that is of illumination, not of brightness” (I have no idea what is meant by this distinction), is that it is the presence of fire or something fire-like. This emphasis on presence is complicated by the existence of shadows, including, even, night itself. If light was solely described as a presence, would it not be that case that everything were illuminated all the time (due to the omnipresence of the sun and other fire-like stuff around the earth).
This could be resolved by Aristotle’s conceding to Empedocles that light (like Aristotle believes of sound and odor already) travels. But he will not, so it is necessary to add to presence a second property of light — directionality — while maintaining, though, that this does not imply travel. Why was it that Aristotle could grant that sound and odor travel, but not allow for the travel of light (only its presence and directionality)? This insistence on the distinction between directionality and travel makes me wonder, even though no mention of such a demonstration is made here, if Aristotle’s insistence that light does not travel, but sound does, was determined empirically. There are ways to devise trials in which the travel time, and differences thereof, of sounds are perceptible and obvious, but the immense speed of light makes it logistically very difficult to observe the travelling of light (probably impossible without advanced and precise measurement apparatus, and thus to Aristotle).
But regardless how Aristotle came to insist that light cannot travel. He finds ways to circumvent the problems it creates. Perhaps light, as a property, cannot travel, but rays (material entities bearing light-like properties?) can travel, as from the sun or from our sense mechanism within the eye outward to the thing being seen and back to the eye.
The remainder of Sorabji’s overview deals with imperceptibles (of time, size, light, sound, distance, etc.). This seems to be a version of the philosophical concern of limits so interesting to medieval scholars. These conversations are complicated and rely upon distinctions between what is imperceptible, what is strongly perceptible (what might be called observable), and what is weakly perceptible (contributes to the observability of the sensory information it, in part, composes?) Aristotle denied imperceptible time. Sorabji probes this by wondering, given that Aristotle acknowledge that sound traveled, and that two sounds could originate from points that were imperceptibly distant from one another, shouldn’t the differences in arrival time likewise be imperceptible? I speculate that perhaps Aristotle could not grant this because it could be argued with sophistry that (knowing that Aristotle grants that sound travels, meaning that sound’s arrival is not instantaneous), if the time difference between two sounds, originating an imperceptible distance from one another were considered imperceptible, then the perception of the arrival time of a sound to travelling over a great distance could be said to be imperceptibly small, the distance being the sum of very many imperceptibly small differences. Sorabji also adds that Aristotle’s resistance to imperceptible times is that it could be used by proponents of the belief that one cannot perceive more than one sense object at a time. With the possibility of imperceptibly small amounts of time, those proponent could argue that we only think we are perceiving more than one sense object at a time, but we are actually perceiving individual sense objects in such quick perception as to seem simultaneous.
Much of this discussion of the nature of color, light, and imperceptibles, and the categories used to make distinctions, eluded me.
What is this difference between “strongly” and “weakly” perceptible? If light does not travel and Aristotle eventually abandoned the theory that “sight” leaves the eye to capture the impression of the object seen, what is sight? What explains shadows, in Aristotle’s conception? What are the implications for Aristotle granting imperceptible distances, but not sizes or times?
Notes
- 129 – “Colour in On the Soul is what acts on the light in the medium intervening between itself and the observer. More exactly, it acts on the transparency of the medium, when that transparency is in its illuminated state of being actually seeable through.”
- 129-30 – “Another description of colour is that it is the object of sign, but this is used to define sight, not colour.”
- 130 – “In On Sense Perception 3, a thing’s own colour is said to be a boundary or surface, but not the boundary of the body, rather the boundary of the transparency within the body.”
- “The borrowed colour of transparent bodies like the sea is introduced to make clear that transparency, and more precisely its surface, is indeed the seat of colour.”
- “Where does the borrowed colour of the sea come from? Aristotle points out that with rigid bodies — and he is thinking of opaque ones — the appearance of colour, though not its own colour, can be changed by the surroundings.”
- 131-2 – “Light, like colour, receives a functional definition, which is straightforward, and a material definition, which is problematic. It is defined by reference to its function as the state in which the transparent is actually, not just potentially seeable through. . . . It would be sensible to understand that light is the state of the transparent in which one can see colour through it, not just phosphorescence, which Aristotle acknowledges can be seen in the dark.”
- 132 – “The material definition of light, that is of illumination, not of brightness is that it is the presence of fire or something like fire in the transparent, that is, in what is seeable through.”
- “But so far Aristotle has spoken of light as the mere presence in a transparent region of such things as fire or the sun. Mere presence is not enough to explain the directionality of light. Why, for example, are there any shadows at all, including the shadows that constitute night, and lunar eclipse? For the sun and other firelike stuff is present in the universe surrounding the earth, a surrounding all of which is transparent. The requirement of presence does not explain why there is not light round the corners. The awkward theory of daylight is due to the celestial friction in every direction makes the question of shadows even more intractable, but the theory of light as presence creates difficulty enough on its own.”
- What the fuck is going on here
- “The problem would be solved if Aristotle replaced the idea of light as a mere presence by the idea that light travels in straight lines. But, consistently with his theory that light is a presence, he refuses to agree with Empedocles that it travels.”
- “In the latter place, he distinguishes the travel of sounds and odours from the instantaneous existence over a region of light, and of the effect of colour, which he takes to be different from light but equally travel-free.”
- “Even though the effect of colour does not travel, it raises for Aristotle the same question as sounds and odours, namely whether differently stationed observers are perceiving the same thing. Or are they perceiving the same physical object, but each a different instance of the same sense quality.”
- 133 – “Nonetheless, Aristotle recognizes that light would not go round any corners, if it were not being constantly reflected, in unobtrusive ways, without necessarily casting a shadow.
- Still don’t know what this means. How is this so much less intelligible than sorabji on aristotle’s commentators?
- “The facts of geometrical optics put him under great pressure to think in terms of directionality and of something travelling after all, whether or not it is light. He talks of the sun’s rays, and of the reflection of rays or light.” But light, for Aristotle, is only a prerequisite for seeing, and the process of actually seeing involves the directionality of something else.”
- “Throughout the Meteorology, and once in On the Heavens, he speaks of sight travelling out form the eyes. But this theory is rejected in On Sense Perception. In On Generation of Animals, Aristotle says that it does not matter for his purposes whether one thinks of sight as travelling outwards or of an effect coming from the thing seen. It is unclear whether this is a change of mind, or whether he was all along only catering to the more popular view as geometrically equivalent to his. In any case he now prefers the latter view, which still involves the language of travel. He speaks of a change as arriving, from outside, from a distant object and as taking a straight course, or being scattered.”
-
- “The theory that he adopts here . . . is that colour acts on the light in the medium, and the medium in turn acts on the organ of sight.”
- “The situation is, then, that his definition of light as the mere presence of something like fire or the sun in a transparent medium leaves the fire-like stuff too inert to explain geometrical optics. What needs to be added to presence is the idea of a direction of influence. On the other hand when he explains the actual process of vision, for which light is merely a prerequisite, he goes too far when he speaks in terms of travel, whether the travel of sight outwards, a theory he at least eventually rejects, or the travel of the influence of colour inwards. What he needs both for light and for the influence of colour, in order to explain geometrical optics, is the idea of a direction of influence, not the idea of travel part before whole. In fact, in the psychological works, this is probably what he intends. It is hard for anyone not to slip into talk suggesting travel, even when all they want is directionality.”
- 134 – SECTION: RELATION OF LIGHT TO COLOUR
- “Light and colour have both turned out to involve transparency and fire-like stuff for Aristotle. How, then, are they related? Bodies with their own colour are opaque and have their colour confined to a surface. It is the transparent bodies with borrowed colour that are harder for Aristotle to distinguish from bodies filled with light. But they too are said to have their colour only at the surface and I think that there will be a furth major difference if Aristotle means that it is only borrowed colour, not light, that makes transparent bodies seeable. What light does is not to make them seeable, but seeable through. Light is not seen, so much as recognized by using one’s sight and finding that one can see not it, but colours. And one cannot see a body filled with light when it is in direct contact with one’s eye. Light is not, therefore, listed as an object of sight.”
- “I want to address an apparent conflict between his readiness in On Sense Perception to allow that small enough quantities and variations of degree are in a sense imperceptible, and his hostility in the next chapter, 7, as well as in Chapter 3, to imperceptible times. I will first try to bring out the apparent conflict and then to explain it.”
- 135 – apparent paradox between the theoretical continuousness of the color spectrum and the fact that we are capable of only perceiving a finite number of color distinctions.
- Especially given that we can actually see these colors, but we can’t distinguish them from the next infinitesimal hue gradation
- “Be that as it may, because the increment exists potentially in the more exact perception, so also it will not be possible actually to perceive so small a perceptible, if separated. But it will nonetheless be perceptible, for it is already potentially so, and it will be actually so, when added to the whole.”
- How is it that the vocal cords tighten and loosen continuously, but we do not identify an infinitum of tones?
- 136 – “Aristotle’s recognition of items that are in a sense imperceptible ought, one would think, to make room for very small times not being perceptible in a strong sense. Nonetheless, a theory of imperceptible times is attacked in On Sense Perception, where it had been used to defend a pointilliste theory of other colours arising out of tiny juxtaposed dots of black and white. An alternative theory that the dots are superimposed on top of each other is said not to require imperceptible times, because here the dots underneath do not directly affect the eye, but only indirectly by affecting the superimposed colour.”
- SOUND DOES TRAVEL THOUGH, I WONDER HOW THE DISTINCTION CAME ABOUT, BECAUSE, IN A SENSE, YOU CAN DEVISE A DEMO TO SEE SOUND TRAVEL, BUT SUCH A DEMO FOR LIGHT IS MUCH MORE COMPLICATED AND REQUIRES ADVANCED MEASURING DEVICES
- 137 – “One might have thought that Aristotle himself would, in the context of sounds, favour the idea of time lags that were not in a strong sense perceptible. . . . he does in On Sense Perception think that sounds travel, and the notes can presumably travel from distances that differ by amounts too small to be perceptible in a strong sense. If the distances can differ by amounts that are in that sense imperceptible, why should not the differences of arrival time be in the same sense imperceptible?
- PERHAPS BECAUSE HE KNOWS, EMPIRICALLY (ON THE SAME BASIS ON WHICH HE INSISTS THAT SOUND TRAVELS), THAT IF THE DIFFERENCE IN ARRIVAL TIME OF A SOUND FROM POINT AND AN IMPERCEPTIBLY MORE DISTANT SECOND IS NOTHING, THEN THIS COULD BE INTEGRATED OUT TO GREAT DISTANCES WHICH SHOULD HAVE NO PERCEPTIBLE DISTANCE IN ARRIVAL TIME, EXCEPT THEY DO, FROM THE ABOVE SAME DEMO
- Another reason to resist imperceptible times is that it could be used by certain opponents to substantiate the claim that one cannot perceive more than one sense object simultaneously
- In the pseudo-Aristotelian De Audibilibus and understanding of sound as a series of air pressure variance waves with differing frequencies is evident
- 139 – SECTION: SMALLEST PERCEPTIBLE SIZES DENIED
