Page:Our knowledge of the external world.djvu/222

 are any the worse for the doctrine that classes are fictions. What the doctrine is, and why it is not destructive, I will try briefly to explain.

On account of certain rather complicated difficulties, culminating in definite contradictions, I was led to the view that nothing that can be said significantly about things, i.e. particulars, can be said significantly (i.e. either truly or falsely) about classes of things. That is to say, if, in any sentence in which a thing is mentioned, you substitute a class for the thing, you no longer have a sentence that has any meaning: the sentence is no longer either true or false, but a meaningless collection of words. Appearances to the contrary can be dispelled by a moment’s reflection. For example, in the sentence, “Adam is fond of apples,” you may substitute mankind, and say, “Mankind is fond of apples.” But obviously you do not mean that there is one individual, called “mankind,” which munches apples: you mean that the separate individuals who compose mankind are each severally fond of apples.

Now, if nothing that can be said significantly about a thing can be said significantly about a class of things, it follows that classes of things cannot have the same kind of reality as things have; for if they had, a class could be substituted for a thing in a proposition predicating the kind of reality which would be common to both. This view is really consonant to common sense. In the third or fourth century. there lived a Chinese philosopher named Hui Tzu, who maintained that “a bay horse and a dun cow are three; because taken separately they are two, and taken together they are one: two and one make three.” The author from whom I quote says that Hui Tzu “was particularly fond of the quibbles