ABSTRACT
Often when we ask what is a so-and-so, we expect a clear and definite answer. If, for example, someone asks me what is a rational number, I may give the simple and precise answer that a rational number is the ratio of two integers. There are other kinds of simple questions for which a precise answer can be given but for which in ordinary talk a rather vague answer is usually given and accepted. Someone reads about nectarines in a book, but has never seen a nectarine, or possibly has seen nectarines but is not familiar with their English name. He may ask me, “What is a nectarine?” and I would probably reply, “A smoothskinned sort of peach.” Certainly, this is not a very exact answer, but if my questioner knows what peaches are, it may come close to being satisfactory.
