pearance to an unknown reality is nothing but the transition from one empirical fact to another, both of which can be known equally well. And what is evident from these examples is a special case of a most general insight: just as in this case there would be no sense in speaking of atoms at all unless they were empirical facts about which we can make any number of verifiable assertions, so there is no meaning in a sentence that speaks of anything in the world as absolutely unknowable, i.e. as beyond the reach of every possible experience.
Every proposition is essentially verifiable. This is the short fundamental principle of philosophizing; we shall do well to devote the rest of our time to its elucidation.
Wherever we assert anything we must, at least in principle, be able to say how the truth of our assertion can be tested, otherwise we do not know what we are talking about; our words do not form a real proposition at all, they are mere noises without meaning. (This must be admitted by every one who ask himself sincerely and carefully how he becomes aware of the meaning of a proposition.) What criterion have we to find out whether the meaning of a sentence has been grasped? How can I assure myself, for instance, that a pupil has properly understood the sense of a proposition which I try to explain to him?
There is only one answer, and it is this: a person knows the meaning of a proposition if he is able to indicate exactly the circumstances under which it would be true (and distinguish them from the circumstances which would make it false). This is the way in which Truth and Meaning are connected (it is clear that they must be connected in some way). To indicate the meaning of a proposition and to indicate the way in which it is verified are identical procedures.
Every proposition may be regarded as an answer to a question, or (if the question is difficult) as the solution of a problem. A sentence which has the grammatical form of a question (with an interrogation mark at the end) will have meaning only if we can indicate a method of answering it. It may be technically impossible for us to do what the method prescribes, but we must be able to point out some way in which the answer could be found. If we are, in principle, unable to do this, then our sentence is no genuine question at all. And where there is no question there can be no
