|
|
|
|
|
|
|
You also can say, with some risk, that box cars are boxes, tank cars are cylinders, and both boxes and cylinders are containers.
The reason it is risky to say, for example, that a box car is a box is that the meaning of is is different from the meaning of is when you say that a box car is a railroad car. When you say that a box car is a box, you are really thinking of the entire box car as though it were one of its parts, which happens to be a kind of container. When you say that a box car is a railroad car, you mean that a box car, as a whole, is a kind of railroad car.
The reason the distinction is important is that properties of parts do not necessarily transfer to wholes—a box-car's door may be new, whereas the corresponding box car may be ancient. Accordingly, you must be exceedingly careful when you say that an object belongs to a class to which, more precisely, one of the object's parts belongs.