Plainly one of the most powerful of philosophical stimuli is the search for security — the infallible knowledge of incorrigible propositions.... To say anything signficiantly about the world we must bring in some thing other than immediate experience..., namely the past and future, and absent objects, and other persons, and unrealised possibilities, and general and hypothetical judgments, and so forth.... We cannot speak without incurring some risk, at least in theory; the only way of being absolutely safe is to say absolutely nothing; that is the goal towards which the search for 'fundamental propositions' asymptotically tends.