When we tackle a philosophical problem, we have no choice but to start from our present beliefs; but in the course of "thinking on these things" we may reject some of our beliefs on the grounds that they conflict with others that we are not prepared to reject. To give an example, we might start off with the belief that we have free will, but abandon it on grounds that it conflicts with certain of our scientific beliefs. Or we might abandon the latter on the grounds that they conflict with our belief in free will. Which direction we take depends on what?