Topics Perception

Question If you watch a car drive away from you down a straight road, it appears to get smaller as it gets farther away. We know that it doesn't really get smaller, it only appears to get smaller. So we distinguish between the real size of the car and the apparent size (at a particular distance). I have two problems with this. First, at what distance do we see the real size; or, at what distance does the apparent size equal the real size? Second, the real car is supposedly outside our heads and the apparent car is supposedly an image of the real car, and inside our heads. But the car we actually see is (a) outside our heads, so real, and (b) changing its size with distance, so an image inside our heads: but how can it be both?

Accepted:
November 15, 2005

Comments

There are tensions here, I agree, though I think they reside in the way that we talk about appearances rather than in the appearance/reality distinction itself--at least as it applies to cars.

Size is an intrinsic property of a car if any property is--that is, a car's size, like its shape, depends entirely upon the way it alone is, and not upon what may or may not hold in the world around it. Apparent-size, by contrast, is a non-intrinsic or relational property of a car, and subtly so: a car's apparent-size depends not just upon the car's size, but also upon the relative location of the relevant viewer. Thus, the car's apparent-size (to Fred) can shrink if the car shrinks in size, but also (and using less magic) if Fred and the car move apart so that light from the car subtends a smaller angle in Fred's visual field (as they say). So, one and the same real car can consistently maintain its size and change its apparent-size through changes only in the relative position of the viewer.

This is all pretty obvious once it's pointed out, but interestingly, it remains a source of confusion nevertheless. This is probably because our judgment of a car's apparent-size seems to come straight from our perception of the car alone, and so to present itself from the inside as if it were an intrinsic property of the car we see. And it's this, I think, that gives rise to your second worry: the only type of size real cars have is the type that doesn't generally change when they drive away; but there's another type of size--apparent-size--that does change; and so, there must be something other than a real car--perhaps a "mental car" or an image of the car--that undergoes a change in this type of size.

But here's where we need to remind ourselves that the real car can undergo a change in apparent-size, while maintaining its size and all its other intrinsic properties, simply because a change has taken place in its relation to the viewer. This is no different than the way I can become an uncle without undergoing any intrinsic change--in fact I can do it obliviously and in my sleep while my sister does all the work in a maternity ward across the country. Unlike uncle-hood, however, apparent-size may not appear from the inside to be changable in this extrinsic way. But it is.

(By the way, how exactly we should draw the distinction between intrinsic and extrinsic properties (and whether the distinction is fully determinate) is a deep philosophical problem. But the point I'm making here doesn't really rely on this distinction so much as on the claim that apparent-size involves one more degree of relationality (or one more relata--a viewer) than does size simpliciter. The point generalizes to relational properties like closeness: the apparent closeness of Jack and Jill to one another depends upon how close together they are and upon their relative distance from the relevant viewer.)

Your first question brings out an additional complexity in our talk of appearances. You ask: at what distance does apparent-size equal real size? If you're asking for a comparative measurement, I'm inclined to reply that one can't be made. Size and apparent-size are different properties (with different degrees of relationality), and so the question makes no more sense than asking when a thing's mass equals its weight. But there's another interpretation, involving a related sense of "apparent", on which your question makes good sense. Sometimes we use "apparent" and "apparently" to mark the properties an object seems to have in perception when we recognize or even know that its actual properties may differ. The stick in the glass of water is apparently crooked even though we know that it's straight (because we're familiar with this illusion). In this sense, the apparent-size of the car is the same as its actual size when the size we perceive it to have is the same as its actual size. Compare: the apparent crookedness of the stick is the same as it's actual crookedness, because there is, it turns out, no water in the glass.

The puzzle that arises out of all of this, though, is how we should distinguish a feature that we perceive something to have from a feature we judge it to have all things considered--including not only what is given to us by perception, but also the various other things we know about the situation at hand, and about the way the world works generally. The distinction seems unproblematic in the (original) case of the stick in the glass of water. We have no problem saying that we perceive the stick to be crooked, but that we do not judge it to be so. And that in this case our knowledge of the illusion overrides the verdict of our perception in our judgment-formation. But what do we say about cases where we accommodate to the odd way that seen properties might display themselves in our perceptions, and then see right through this? Suppose I watch cars drive along a distant road. At first, they're mere dots on the horizon, but I soon get used to judging their relative sizes, and do so accurately. Suddenly a very large dot moves along, much larger than any I've seen. I judge it to be an absolutely enormous vehicle--one of those monster-trucks used to move construction equipment. Does it appear any different in perception?