Page:Schlick - Gesammelte Aufsätze (1926 - 1936), 1938.djvu/240

 Nevertheless it is the right answer and it can be reconciled, if it is only properly understood. We must take great care, for misunderstanding at this point is very easy and very dangerous.

It cannot be doubted or denied that in a certain sense our symbols must point to content, for our propositions speak of the real world, and content is reality. (It must be remembered that my sentences do not have the ambition to be propositions themselves, their purpose is to give a certain direction to the reader's attention). But this cannot mean that our propositions really say anything about content, for the reasons we gave for the impossibility of this are perfectly valid and cannot be overthrown by an analysis of the nature of science. And the same reasons must in the end show us the way to the solution of the problem.

Let us start by considering an example in physics in which the same structure is used to describe many essentially different physical processes. There is a certain differential equation, the so-called wave equation, which applies to the propagation of waves of any kind, e.g. sound, radio waves, Röntgen rays. What is the difference between these various things which obey the same formal law? In the case of sound the waves are formed by mechanical vibrations of material particles, air molecules, for instance —, in the case of radio waves and Röntgen rays we have to do with oscillations of "electric and magnetic forces" (if we use the language of Maxwell's theory, leaving aside the most recent development). Now air molecules and electric forces are utterly different in their physical nature; although both of them may exhibit a certain behaviour that is expressed by the same wave equation, there are innumerable other formulae which are true for the one but not for the other, which means that they differ completely in their structures. So we see that at this point we do not have to have recourse to content at all; the signs substituted for the variables occurring in the wave equation stand for various structures, not for content. But you will say: as long as this is the case the new signs will be nothing but variables either; the word "electric force", for instance, will have no definite meaning, but will signify any entity that fulfils certain axioms (these axioms, in the classical theory, will be Maxwell's fundamental equations), and there may be innumerable such entities; which of these is really meant? Before this question is answered our formal system will