The longer you ponder materialism, the graver the difficulties that present themselves. How can materialism account for the fact that we consider our accounts of the world to be not merely chemically generated reactions but true beliefs? British biologist J. B. S. Haldane sums up the problem: “If my mental processes are determined wholly by the motions of atoms in my brain, I have no reason to suppose my beliefs are true… and hence I have no reason for supposing my brain to be composed of atoms.” Physicist Stephen Hawking takes upthe horns of this dilemma and finds himself impaled: