To take in the importance of Peirce’s principle, one must get accustomed to applying it to concrete cases.  I found a few years ago that Ostwald, the illustrious Leipzig chemist, had been making perfectly distinct use of the principle of pragmatism in his lectures on the philosophy of science, tho he had not called it by that name.

“All realities influence our practice,” he wrote me, “and that influence is their meaning for us.  I am accustomed to put questions to my classes in this way:  In what respects would the world be different if this alternative or that were true?  If I can find nothing that would become different, then the alternative has no sense.”

That is, the rival views mean practically the same thing, and meaning, other than practical, there is for us none.  Ostwald in a published lecture gives this example of what he means.  Chemists have long wrangled over the inner constitution of certain bodies called ‘tautomerous.’  Their properties seemed equally consistent with the notion that an instable hydrogen atom oscillates inside of them, or that they are instable mixtures of two bodies.  Controversy raged; but never was decided.  “It would never have begun,” says Ostwald, “if the combatants had asked themselves what particular experimental fact could have been made different by one or the other view being correct.  For it would then have appeared that no difference of fact could possibly ensue; and the quarrel was as unreal as if, theorizing in primitive times about the raising of dough by yeast, one party should have invoked a ‘brownie,’ while another insisted on an ‘elf’ as the true cause of the phenomenon.” [Footnote:  ’Theorie und Praxis,’ Zeitsch. des Oesterreichischen Ingenieur u.  Architecten-Vereines, 1905, Nr. 4 u. 6.  I find a still more radical pragmatism than Ostwald’s in an address by Professor W. S. Franklin:  “I think that the sickliest notion of physics, even if a student gets it, is that it is ’the science of masses, molecules and the ether.’  And I think that the healthiest notion, even if a student does not wholly get it, is that physics is the science of the ways of taking hold of bodies and pushing them!” (Science, January 2, 1903.)]

It is astonishing to see how many philosophical disputes collapse into insignificance the moment you subject them to this simple test of tracing a concrete consequence.  There can be no difference any-where that doesn’t make a difference elsewhere—­no difference in abstract truth that doesn’t express itself in a difference in concrete fact and in conduct consequent upon that fact, imposed on somebody, somehow, somewhere and somewhen.  The whole function of philosophy ought to be to find out what definite difference it will make to you and me, at definite instants of our life, if this world-formula or that world-formula be the true one.