Part 2

Shadows; Unlocking Their Secrets, from Plato to Our Time
by Roberto Casati

(Page 2 of 2)

Now let's try to focus on the situation of the prisoners.

The first fact is that there was no reason to use shadows for this experiment. The statues, the marionettes, would have sufficed. To be perfectly logical, even flesh-and-blood actors would have served to make us ponder the distinction between image and reality. Why did Plato choose shadows? One answer is that shadows are a disturbing example of lesser entities: they are a diminution of the objects that project them. They are flat, immaterial, and without qualities, without color. Their outlines enclose an indistinct interior. But above all they are absences, negative things. A shadow is a lack of light. Negative things are bizarre. In the end, actors and attendants are on the payroll of the theater. Even marionettes are counted, during inventory. But shadows are not listed anywhere. These uncertain beings confuse the mind; they trouble us. As if that weren't enough, shadows have always been surrounded by suspicion and fear. They are strange entities: we don't know much about them, but we do know that they're not a happy bunch. Plato is right to use them if he wants to worry us.

There's more. For Plato it went without saying that shadows keep us at a certain remove from knowledge. They are a screen between the prisoners and the truth. And yet, despite their unhappy condition, despite the fact that the theater's paltry tricks impose a distance between them and reality - despite all this, the prisoners have some reason for optimism. They can study the shadows carefully. They can reconstruct the three-dimensional forms of the objects casting the shadows. They can grasp the mathematical beauty of the relationship between an object and its shadow. Approached in a certain way, the shadows turn out to be a magnificent tool for knowledge. This is why in the final analysis Plato's experiment is not convincing. Shadows can be used to reconstruct the world. And indeed we continually use them to understand the shape of our environment.

Just Imagine a World Without Shadows

If light is the instrument of vision, shadow must be its great antagonist. One hides in the shadows because a searcher's gaze cannot penetrate the darkness. But it's also true that vision can't do without shadow: the information carried by shadow is a fundamental aid to seeing. Evolution has recognized that the world is full of shadows and it has selected biological systems that adapt to levels of darkness. Why do many animal species have bellies paler than their backs? Because light comes mostly from above: the pale spot on the belly counteracts the inevitable shadow. Thus the animal hardly stands out, and he is less easy to see. Here evolution was betting on the fact that the visual system of the predator was hunting for shadows.

Things could have gone differently. Permit me to develop this hypothesis, though I'll need to rewrite the laws of physics. Let's say that all the objects in the universe were dimly phosphorescent. The slight bit of light they gave off would make only weak shadows. But these shadows would fall on phosphorescent surfaces and be canceled out. In such a universe evolution would have had no reason to create eyes that notice shadow, as was the case in our world. Our vision is so bewitched by chiaroscuro that if we were to find ourselves suddenly in a shadowless world, everything would seem insubstantial and without depth.

Here's another example of a world without visible shadows. If our eyes were fitted with lamps, we would never see the shadows they cast: the shadow would always be hidden by the object making the shadow. The sun's view of the world is immaculate because the sun "has not yet alighted on shadow," as Goethe wrote in Faust.

Immaculate it may be; but it certainly is flat. Rooms and faces photographed with a flash are flat. In images where we have erased the shadows, objects are flat and they lack context.

The opposite is also true: erasing the light eliminates relief. In what may have been the first experiment ever conceived of in cognitive science, Galileo Galilei (1564-1642) suggested blackening the unshadowed parts of a statue in order to eliminate the chiaroscuro. His hypothesis was that the statue would appear to be without relief - flat. Galileo wanted to show the superiority of painting over sculpture. In modern terms, the experiment shows that it's not enough to have good volume in order to look like an object with good volume: you also have to make the right impression. Putting on makeup does the same thing: augmenting the darkness of a part that's slightly shadowed gives your face the appearance of greater depth.

Cast shadows have been removed from this painting by Jean-Baptiste-Siméon Chardin, Copper Urn. As a result, the objects are "floating." Then the contrast was eliminated from the picture, and it was lightened. As a result, the objects lose their solidity. (Graphic manipulation by W. Criscuoli.)

But what can be said about the world that so frightened Plato, a world in which perception depends on shadows exclusively? We know part of the answer. In 1953 the psychologists Hans Wallach and D. N. O'Connell actually carried out a variation on the cave experiment. First they took a piece of stiff wire and bent it irregularly. Then they hid it behind a screen and had a lamp project a shadow of the wire. All the observers saw was the shadow of the bent wire on the screen. If the wire stayed still, observers would see a stringy black mark like a hand-sketched line. But the wire was actually mounted on a turntable. As soon as the turntable began to move, the projection of the shadow on the screen changed. Just as in Plato's cave, all the observers had to work with were the dancing shadows, two-dimensional figures playing tag. But they did not in fact perceive a deformed black mark stretching and shrinking: they had the distinct impression of a three-dimensional wire spinning in space. The brain works feverishly to extract solid structures from a changing reality of shifting perspectives. One might say these observers are different from the prisoners in the cave; Wallach and O'Connell's observers were not kept in chains and obligated to look only at shadows from infancy. Their brains could have learned to see three-dimensional things, while those of Plato's prisoners might have been affected by their strange upbringing in the cave. But it's also true that for countless generations our ancestors brains were immersed in a world of rigid three-dimensional objects, and we inherited a propensity to see solid things. This propensity kicks in on the slightest pretext and makes us see objects even where there is nothing but shadows. In a world made entirely of shadows, our brains might manage better than Plato suspected.

Certainly, we now know more about perception than was known in ancient Greece (although the experiment by Wallach and O'Connell requires equipment so simple that it could have been done in the fifth century b.c.: just replace the turntable with a turning lathe). Are we being unfair to Plato?

Copyright © 2003 by Roberto Casati.

About the Author

Roberto Casati was born in Milan in 1961. A research director at the Centre National de la Réchérche Scientifique, he lives in Paris and works at the Institut Nicod, a laboratory of the École des Hautes Études en Sciences Sociales and of the École Normale. He studies the cognition of strange things - images, colors, sounds, places, holes - and shadows. With Achille Varzi he is the author of Holes and Other Superficialities and Parts and Places.