number is to ask some such question as whether it is possible to translate propositions about the natural numbers into propositions about classes. 3 And the same thing applies to all the other philosophical questions of the form, "What is an x?" or, "What is the nature of x?" They are all requests for definitions, and, as we shall see, for definitions of a peculiar sort.
Although it is misleading to write about linguistic questions in "factual" language, it is often convenient for the sake of brevity. And we shall not always avoid doing it ourselves. But it is important that no one should be deceived by this practice into supposing that the philosopher is engaged on an empirical or a metaphysical enquiry. We may speak loosely of him as analysing facts, or notions, or even things. But we must make it clear that these are simply ways of saying that he is concerned with the definition of the corresponding words.
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