Читать книгу This Is Metaphysics - Kris McDaniel - Страница 15

1.5 Let’s start with something that seems easy. Think about this list of things: a cat, a dog, a kangaroo, a fish, and a loaf of bread. Suppose you were asked, “Which one of these things does not belong with the others?” I don’t think you’d have a problem answering. You’d unhesitatingly single out the loaf of bread. This wouldn’t even be a hard question for a small child. My five‐year old unhesitatingly singled out the loaf of bread too.

1.6 Suppose we take out the loaf of bread from the list and ask again, “Which one of these things does not belong with the others?” You might struggle a bit more this time, but you’d probably exclude the fish, although that isn’t the only defensible answer. For example, you might exclude the fish because each of the remaining three is a mammal. However, you might instead exclude the kangaroo on the grounds that each of the remaining three is commonly taken as a pet. (Even in Australia, it is not very common for someone to have a pet kangaroo.)

1.7 But suppose I gave you the following list of things: a neutron star, the number 2, the dream you had last night, and a blade of grass. Now the question “Which one of these does not belong with the others?” is much harder to answer. Why is this? I suggest that it is because any way of excluding one of these items from the list leaves us with a list of three things that don’t really belong together any more than the original four. And you recognize, at least implicitly, this fact.

1.8 But why do some groups of things belong together while other groups of things do not? A complete answer to this question requires some metaphysics: specifically, we need a theory that explains what belonging together amounts to in general. This theory will be a metaphysical theory of classification. (We’ll discuss this further in the Section 1.5.)

1.9 A classification of a group of things is just a way of breaking up that group of things into groups. Let’s say that a classification of things is a good way of classifying things when it breaks things into groups, and anything in one of those groups belongs with all the other things in that group but doesn’t belong with the things that are in a different group. Venn diagrams provide a good way of illustrating this idea.¹ Suppose we have a group of things w, x, y, and z.

Suppose that w and x belong together and that y and z belong together, but also that no collection of exactly three of them belong together. Then a good classification would divide up our initial group of four things into two groups of two things. We could represent this classification with a picture:

In this classification w and x have been put together and separated from y and z, and y and z have also been put together.

1.10 So far, we have kept things pretty simple. One complication is that belonging together probably comes in grades or degrees. That is, some things will belong together to a greater extent than other things. Think about this list of things: me, my wife, my two daughters, and my dog Ranger. Ranger is the odd man (odd dog?) out in this list. But now consider a larger list: me, my wife, my daughters, my dog Ranger, and the number 2. Despite being even, the number 2 is the odd number out. What this shows is that although Ranger doesn’t belong in the first group as much as my daughters do, he definitely belongs in the second group much more than the number 2. So, he must belong with me, my wife, and my daughters to some extent.

1.11 What this means is that instead of focusing simply on the question of whether a specific classification is a good way of classifying, we should also consider the more general question of when a given classification is a better classification than another. We won’t have a complete theory of classification if we don’t consider this more general question.

1.12 The second complication is that there are different reasons why we judge that things belong together, and these different reasons will sometimes lead to different and apparently conflicting ways of classifying objects. But these different ways of classifying objects don’t really conflict. We already saw an illustration of this phenomenon. Let’s return to one of the lists of things that we thought about at the beginning, specifically the one that consisted of a cat, a dog, a kangaroo, and a fish. There seemed to be two equally respectable ways of breaking this list into groups. We might separate the fish from the remaining three on the grounds that the remaining three are mammals; but we may also separate the kangaroo from the remaining three on the grounds that only the remaining ones are commonly taken as pets. Is there any point in trying to decide which of these two classifications is better? Isn’t how we classify things largely dependent on what we are interested in, what we care about, what we desire, and so forth?

1.13 Sort of. There’s an important difference between the two kinds of classifications just mentioned. One of them classifies animals by looking to see whether they are related to us in some interesting social way: the classification that excludes kangaroos is based on the observations that we don’t interact with kangaroos in (some of) the ways in which we interact with dogs, cats, and fish. But it wasn’t inevitable that we don’t typically have kangaroos as pets. Imagine a possible situation in which we have kangaroos as pets instead of cats: if that possible situation had actually happened, then we probably would have felt that it was cats rather than kangaroos that do not belong on the list.

1.14 But now think about the other kind of classification, the one that excludes fish because they are not mammals. This classification isn’t based on our desires or interests, and it doesn’t classify things on the basis of how these creatures relate to us. Mammals could have existed even if no human beings had ever evolved on the planet. And mammals still would have belonged with each other in a way that cats, dogs, fish, and kangaroos do not. Moreover, we can’t easily imagine possible scenarios in which, for example, dogs fail to be mammals. We can imagine possible situations in which there are things that have the same outward physical appearance as dogs and that have similar behaviors to dogs, which aren’t themselves mammals. But that’s not the same thing as imagining a situation in which dogs aren’t mammals.

1.15 One lesson to draw from these observations is that, roughly, there can be (at least) two kinds of systems of classification. We might classify objects because we are interested in how they relate to us. We can think of these as subjective classification systems because they are driven by our interests, desires, values, and so on. But a system of classification might also classify things on a more objective basis, that is, on grounds that are independent of whether that system of classification reflects anything about how reality relates to us or what we care about. Some things objectively belong together. An objective classification system is one that classifies things together in a way that matches how they objectively belong together.