"One assault on the world of facts was launched some time ago from the direction of the theory of knowledge. This campaign was primarily waged by those who aimed to discredit the empiricist belief that our world consists of sense data capable of being directly perceived and uncontentiously described. It would not be too much to say that by now this particular dogma of empiricism has fallen into very general disrepute. Scarcely anyone nowadays believes in the possibility of building up structures of factual knowledge on foundations purporting to be wholly independent of our judgements."