Everyone is enough of an empiricist to believe that we learn from experience and no one is so far removed from rationalism as to deny that ideas play a vital role in the theories we construct about the world. But it is only too easy, and perhaps too tempting, for philosophers with a pronounced empiricist or rationalist bias to caricature the position of their opponents and make them appear as holding ludicrously simplistic views about the nature of scientific knowledge. In fact, any philosophical position worth its salt has a built-in flexibility or a power to accommodate, sometimes with surprising comfort, theses that seem central to rival theories. The Leaning Tower experiment, however fictitious, is equally well explained by rationalists or empiricists. Facts, however hard or obdurate, have a way of lending themselves to varying interpretations. Properly marshalled, they can be enlisted to serve any good philosophical cause.