F. C. S. Schiller's first book "Riddles of the Sphinx" was published before he became aware of the growing pragmatist movement taking place in America. In it, Schiller argues for a middle ground between materialism and absolute metaphysics. These opposites are comparable to what William James called tough-minded empiricism and tender-minded rationalism. Schiller contends on the one hand that mechanistic naturalism cannot make sense of the "higher" aspects of our world. These include free will, consciousness, purpose, universals and some would add God. On the other hand, abstract metaphysics cannot make sense of the "lower" aspects of our world (e.g. the imperfect, change, physicality). While Schiller is vague about the exact sort of middle ground he is trying to establish, he suggests that metaphysics is a tool that can aid inquiry, but that it is valuable only insofar as it does help in explanation.