There is truth in my idea that really in my thinking I am only reproductive. I believe that I have never invented a new line of thought: that has always been given me by someone else. I have only seized on it immediately with a passionate urge for the work of clarification. That is how Boltzmann, Hertz, Schopenhauer, Frege, Russell, Kraus, Loos, Weininger, Spengler, Sraffa influenced me.1