man who has not only seen a great deal but also knows how to profit from it for his actions. It is in this second sense (by the way, the sense the word has in Hume’s and Kant’s philosophy) that verifiability must be declared to be independent of experience. The possibility of verification does not rest on any ‘experiential thruth’, on a law of nature or any other true general proposition, but is determined solely by our definitions, by the rules which have been fixed for our language, or which we can fix arbitrarily at any moment. All of these rules ultimately point to ostensive definitions, as we have explained, and through them verifiability is linked to experience in the first sense of the word. No rule of expression presupposes any law or regularity in the world (which is the condition of ‘experience’ as Hume and Kant use the word), but it does presuppose data and situations, to which names can be attached. The rules of language are rules of the application of language; so there must be something to which it can be applied. Expressibility and verifiability are one and the same thing. There is no antagonism between logic and experience. Not only can the logician be an empiricist at the same time; he must be one if he wants to understand what he himself is doing.
IV
Let us glance at some examples in order to illustrate the consequences of our attitude in regard to certain issues of traditional philosophy. Take the famous case of the reality of the other side of the moon (which is also one of Professor Lewis’s examples). None of us, I think, would be willing to accept a view according to which it would be nonsense to speak of the averted face of our satellite. Can there be the slightest doubt that, according to our explanations, the conditions of meaning are amply satisfied in this case?
I think there can be no doubt. For the question, ‘What is the other side of the moon like?’, could be answered, for instance, by a description of what would be seen or touched by a person located somewhere behind the moon. The question whether it be physically possible for a human being — or indeed any other living being — to travel around the moon does not even have to be raised here; it is entirely irrelevant. Even if it could be shown
