So far as he is concerned, he has repudiated the idea that science is purely utilitarian in the most emphatic language. August Comte said that it would be idle to seek to know the composition of the sun, since this knowledge would be of no use to sociology. Against such a charge of uselessness Poincaré eloquently defended his science by showing the practical value of astronomy even from Comte's point of view, but in conclusion asserted his own opinion very plainly:
Was I wrong in saying that it is astronomy which has made us a soul capable of comprehending nature; that under heavens always overcast and starless, the earth itself would have been for us eternally unintelligible; that we should there have seen only caprice and disorder; and that, not knowing the world, we should never have been able to subdue it? What science could have been more useful? And in thus speaking I put myself at the point of view of those who only value practical applications. Certainly, this point of view is not mine; as for me, on the contrary, if I admire the conquests of industry, it is, above all, because they free us from material cares, they will one day give to all the leisure to contemplate nature. I do not say: Science is useful, because it teaches us to construct machines. I say: Machines are useful, because in working for us, they will some day leave us more time to make science. But finally it is worth remarking that between the two points of view there is no antagonism, and that man having pursued a disinterested aim, all else has been added unto him.--"Value of Science", p. 88.
It is this insistence upon the æsthetic value of science that caused him to shrink from being called a "pragmatist", although those who accept that name have always laid unusual stress upon the æsthetic factor in thinking. But in his theory of knowledge Poincaré is decidedly pragmatic, and no one has given a clear exposition or stronger expression to the practical mode of thought by which the natural sciences have made their progress and which is now being extended to the fields of metaphysics, religion, ethics, and sociology. Poincaré's favorite word is "convenient" (_commode_). Theories are strictly speaking not to be classed as true or false. They are merely more or less convenient. For example: