The one series of sciences seems not to recognize the question, but replies clearly and exactly to its own independent questions: that is the series of experimental sciences, and at the extreme end of it stands mathematics. The other series of sciences recognizes the question, but does not answer it; that is the series of abstract sciences, and at the extreme end of it stands metaphysics.

From early youth I had been interested in the abstract sciences, but later the mathematical and natural sciences attracted me, and until I put my question definitely to myself, until that question had itself grown up within me urgently demanding a decision, I contented myself with those counterfeit answers which science gives.