proposition mean?” You see, there would never be any end to this kind of inquiry, the meaning could never be clarified, if there were no other way of arriving at it than by a series of propositions.
An example will make the above clear, and I believe you will all understand it immediately. Whenever you come across a difficult word for which you desire to find the meaning you look it up in the Encyclopedia Britannica. The definition of the word is given in various terms. If you don't happen to know them you look up these terms. However, this procedure can't go on indefinitely. Finally you will arrive at very simple terms for which you will not find any explanation in the encyclopedia. What are these terms? They are the terms which cannot be defined any more. You will admit that there are such terms. If I say, e. g., that the lamp shade is yellow, you might ask me to describe what I mean by yellow — and I could not do it. I should have to show you some color and say that this is yellow, but I should be perfectly unable to explain it to you by means of any sentences or words. If you had never seen yellow and I were not in a position to show you any yellow color it would be absolutely impossible for me to make clear what I meant when I uttered the word. And the blind man, of course, will never be able to understand what the word stands for.
All of our definitions must end by some demonstration, by some activity. There may be certain words at the meaning of which one may arrive by certain mental activities just as I can arrive at the signification of a word which denotes color by showing the color itself. It is impossible to define a color — it has to be shown. Reflection of some kind is necessary so that we may understand the use of certain words. We have to reflect, perhaps, about the way in which we learn these words, and there are also many ways of reflection which make it clear to us what we mean by various propositions. Think, for example, of the term “simultaneity” of events occurring in different places. To find what is really meant by the term we have to go into an analysis of the proposition and discover how the simultaneity of events occurring in different places is really determined, as was done by Einstein; we have to point to certain actual experiments and observations. This should lead to the realization that philosophical activities can never be replaced and expressed by a set of propositions. The discovery of the meaning of any proposition must ultimately be achieved by some act, some immediate pro-
