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The physicist, in his study of natural phenomena, has two methods of making progress: (1) the method of experiment and observation, and (2) the method of mathematical reasoning. The former is just the collection of selected data; the latter enables one to infer results about experiments that have not been performed. There is no logical reason why the second method should be possible at all, but one has found in practice that it does work and meets with remarkable success. This must be ascribed to some mathematical quality in Nature , a quality which the casual observer of Nature would not suspect, but which nevertheless plays an important rôle in Nature's scheme.
P. A. M. Dirac (Mon,) studied this question.