It is clear that in order to understand a verbal definition we must know the signification of the explaining words beforehand, and that the only explanation which can work without any previous knowledge is the ostensive definition. We conclude that there is no way of understanding any meaning without ultimate reference to ostensive definitions, and this means, in an obvious sense, reference to ‘experience’ or ‘possibility of verification’.
This is the situation, and nothing seems to me simpler or less questionable. It is this situation and nothing else that we describe when we affirm that the meaning of a proposition can be given only by giving the rule of its verification in experience. (The addition, ‘in experience’, is really superfluous, as no other kind of verification has been defined.)
This view has been called the “experimental theory of meaning”; but it certainly is no theory at all, for the term ‘theory’ is used for a set of hypotheses about a certain subject-matter, and there are no hypotheses involved in our view, which proposes to be nothing but a simple statement of the way in which meaning is actually assigned to propositions, both in everyday life and in science. There has never been any other way, and it would be a grave error to suppose that we believe we have discovered a new conception of meaning which is contrary to common opinion and which we want to introduce into philosophy. On the contrary, our conception is not only entirely in agreement with, but even derived from, common sense and scientific procedure. Although our criterion of meaning has always been employed in practice, it has very rarely been formulated in the past, and this is perhaps the only excuse for the attempts of so many philosophers to deny its feasibility.
The most famous case of an explicit formulation of our criterion is Einstein’s answer to the question, What do we mean when we speak of two events at distant places happening simultaneously? This answer consisted in a description of an experimental method by which the simultaneity of such events was actually ascertained. Einstein's philosophical opponents maintained — and some of them still maintain — that they knew the meaning of the above question independently of any method of verification. All I am trying to do is to stick consistently to Einstein's position and to admit no exceptions from it. (Professor Bridgman’s book on The
