Descartes and The Blind Man’s Cane

A bit of primary evidence against a strictly representationalist interpretation of Descartes’ theory of knowledge (like the one that many anti-Cartesian, philosophy-of-mindists may presuppose),

From Descartes’ Treatise on Optics:

…it is necessary to beware of assuming that in order to sense, the mind needs to perceive certain images transmitted by the objects to the brain, as our philosophers commonly suppose; or, at least, the nature of these images must be conceived quite otherwise than as they do. For, inasmuch as [the philosophers] to not consider anything about these images except that they must resemble the objects they represent, it is impossible for them to show us how they can be formed by these objects, received by the external sense organs, and transmitted by the nerves of the brain…instead we should consider that there are many other things besides pictures which can stimulate our thought, such as for instance, signs and words, which do not in any way resemble the things which they signify (forth discourse, trans. Olscamp)

Compare this quote with the traditionally assumed anti-Cartesian Wittgensteinian talk about the phenomenology of representations, from his Philosophical Investigations:

273. What am I to say about the word “red”? – That it means something ‘confronting us all’ and that everyone should really have another word, besides this one, to mean his own sensation of red? Or is it like this: the word “red” means something known to everyone; in addition, for each person, it means something known only to him? (Or perhaps rather: it refers to something known only to him.)

274. Of course, saying that the word “red” “refers to” instead of “means” something private does not help us in the least to grasp its function; but it is the more psychologically apt expression for a particular experience in doing philosophy. It is as if when I uttered the word I cast a sidelong glance at the private sensation, as it were to say to oneself: I know alright what I mean by it.

Descartes, in the non-Representational pole of his conception of light and seeing, exactly where you would suspect that a representationalist model would show up to entrench itself, actually appeals to a non-visual mode of perception to indicate what he believes is happening when we see, that of how a blind man uses a cane:

It sometimes doubtless happened to you, while walking in the night without a light through places which are a little difficult, that it became necessary to use a stick in order to guide yourself; and you have then been able to notice that you felt, through the medium of the stick, the diverse objects around you, and that you were even able to tell whether they were trees, or stones, or sand…(first discourse)

…just as when the blind man of whom we have spoken above touches some object with his cane, it is certain that the objects do not transmit anything to him except that, by making his cane move in different ways according to their different inherent qualities, they likewise and in some way move the nerves of his hand, and then the places in his brain where the nerves originate. Thus his mind is caused to perceive as many different qualities in these bodies, as there are varieties in the movements that they cause in his brain…(fourth discourse)

In fact, the way that Descartes is here relating what perception is, is presented to be like the passing of a vibration (as if along the threads of a silk web), instantaneously, in terms of a signification, and not a representation. Descartes in his attempt to distance himself from the Perspectivist tradition, and the notion of “intentional species” [“images flitting through the air”], actually understands in sight a connectivity which makes of a prosthetic cane a similarity to the infinity of rays that pervade the visual universe, so many active strands, which signify states of the world, but do not represent them. He wants to say that we see as a blind man sees.

It is possible of course that Descartes himself fluctuates between a loose picturing conception of knowledge “in order to depart as little as possible from currently accepted belief”, and more rigorously, a signifying conception, fully aware of and attempting to synthesize the difference. What is important though is that some of the characteristic depictions of Descartes’ philosophy are rather incomplete. One of course might say that Wittgenstein is talking about a very different thing than Descartes here. Wittgenstein is talking about how words mean what they mean, and Descartes is talking about sensations and perceptions. But if resemblance is not the determining factor of sensation, how could the sensation itself stand as a supposed anchor point (reference) for the words we use? Descartes, at least in this one way, is approaching Wittgenstein’s Beetle.

Descartes’ Black Cat

To think about just how inordinate Decartes’ thinking about sensation is, consider his example of the cat. He want to talk about how like vibrating threads, rays of light connect to the eye:

…For just as our blind man can sense the bodies which are around him, not only through the action of these bodies when they move against his stick, but also through that of his hand, when they are only resisting it, so we must affirm that objects of sight can be felt, not only by means of the action which, being in them, tends toward the eyes, but also by means of that which, being in the eyes, tends towards them. Nevertheless, because this action is nothing other than light, it is only of those who can see in the darkness of the night, such as cats, in whose eyes this action is found; and that, as for the ordinary man, he sees only by the action which comes from the objects. For experience has shown us that these objects must be luminous or illuminated in order to be seen, and not that our eyes must be luminous or illuminated in order to see them. (first discourse)

What is the purpose of Descartes’ cat? He seems to contradict himself, immediately, as his reasoning unfolds: Like the cane, sight is accomplished not only by receiving light-vibrations from objects, the vibrations can come from eyes towards  objects as well (is he thinking of the glow of cat’s eyes in the dark?), but not in the case of human beings (?). What I suspect is found in the example of the cat is really that Descartes is attempting to articulate a theory of complete connectivity, one in which minds, far from being cut off from each other and possibly from the world, are rather continually connected to the world, through a transversality of instantaneous signifying vibrations. Rays, Canes and Nerves-threads communicate the states of the world, significantly.

This leaves an easy, homuculus-driven comparison of Descartes to Wittgenstein somewhat impaired.

…nevertheless, as I have already shown, we must not hold that it is by means of this resemblance [come from the camera obscura image at the back of the eye] causes us to perceive objects, as there were yet other eyes in our brain with which we could apprehend it.

Dioptrics, sixth discourse, “Vision”

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