David Hume, A Treatise on Human Nature
his refl ected image that he is lost to the real world around him. But what if, as many philosophers have argued, the “reality” that we believe we experience is itself an illusion?
Sometimes it is the things most familiar to us that turn out to be the most deeply puzzling. Take mirrors. How many times do you see yourself
refl ected in a mirror each day? Most of us never stop to think about what we see, but mirrors are philosophically mystifying things.
Take a look at yourself in a mirror. If the mirror before you were replaced by a sheet of glass, and you were to stand behind the glass in just the position your mirror-self seems to
stand, then while your head would still be at the top and your feet at the bottom, your left hand would be over to the right, where your right hand appears in the mirror, and your right hand would be to the left, where your left hand appears.
The mirror puzzle
That is the source of the puzzle: mirrors reverse the left–right orientation we would expect to see if we were standing
in that position, but they leave top and bottom untouched.
What accounts for this peculiar asymmetry?
Some of the world’s greatest minds, including that of the Ancient Greek philosopher Plato (see pp.244–7), have struggled with and been defeated by this mystery.
Notice that this left–
right switch still happens no matter which way up you happen to be. Lie on your side in front of a mirror and see the result. It is still your left and right sides that are switched around, not your head and feet. Nor does it matter which way around the mirror is. Turn it upside down. The effect is exactly the same. Some people suppose that the effect must be due to our having a left and a right eye, rather than a top
A dancer resting beside a mirror demonstrates the puzzling behavior of refl ections. Even when we are horizontal, the mirror still switches our left and right sides around, but not our heads and feet.
Mirrors present an extremely accurate image of ourselves—except for one thing. Our right-hand sides are the left- hand sides of the person in the mirror.
and bottom eye. But that is not the explanation. If you cover one eye, the asymmetric reversal remains, so we must look elsewhere for an answer.
A SCIENTIFIC APPROACH Might science solve the mirror puzzle? In particular, is the explanation that light is refl ected differently left-to-right than it is top-to-bottom? It seems not.
Suppose we hold a clock up in front of a mirror and draw arrows linking each number on the clock face with the same number refl ected in the mirror (see above). The arrows show that the way the mirror refl ects is entirely symmetrical in every direction. The arrows do not cross over top to bottom. But neither do they cross over left-to-right. It is not as if a mirror refl ects rays of light differently depending on whether they are coming from your left and right sides rather than your top and bottom. The light is refl ected in the same way no matter where it happens to land on the mirror.
So the puzzle has absolutely nothing to do with how light is refl ected off the surface of the mirror. Indeed, the puzzle
is not a scientifi c puzzle at all. Even when we know all the scientifi c facts about how mirrors and light behave, that still leaves the mystery of why mirrors reverse one way and not the other.
The more we grapple with this mystery, the deeper it seems to become, and the more mirrors seem to take on an almost magical quality. Just why do they do what they do? The profound sense of baffl ement raised by this question is typical of that raised by philosophical problems more generally.
PROPOSING A SOLUTION What follows is a suggested solution to the mirror puzzle (or at least part of a solution—one or two details need to be fi lled in). I should add, however, that this is my own answer to the puzzle. Whether or not it is a satisfactory one is something that you should judge for yourself.
As we have already seen, in a sense, mirrors don’t reverse anything. But in comparing how your left and right sides
MIND-DEPENDENCE 97