Free Russell - A Very Short Indroduction by A. C. Grayling Page A

later (in Human Knowledge ) he dealt with it by accepting a version of something he otherwise deprecated in the philosophy of Kant, namely, that there have to be some things (other than truths of logic) known to us a priori if knowledge is to be possible at all. This highly important point is discussed in the appropriate place below.
    Another problem advanced by critics is that the considerations Russell relies upon to show that there is an appearance-reality distinction do not, as he states them, persuade. The fact that an object looks one colour or shape to one perceiver but another colour or shape to another perceiver, or different colours or shapes to the same perceiver under different conditions – for example, depending upon whether he sees it in daylight or darkness, or from one viewpoint or another – tells us that the question of how objects appear to perception is a complicated matter, but it does not by itself tell us that we are perceiving something other than the object in question.
    This criticism is valid as it stands, but it happens that there are other perfectly adequate ways of drawing an appearance-reality distinction, as more recent work in the philosophy of perception shows; so Russell’s arguments here can be regarded – as he regarded them himself – as heuristic, that is, as merely illustrating the point in order to get discussion started.
    But this criticism suggests a further and more important one. It is that Russell, like all his predecessors since Descartes and like some of his successors such as H. H. Price and A. J. Ayer, accepted a crucially significant assumption from Descartes. This is that the right startingpoint for an enquiry into knowledge is individual experience. The individual is to begin with the private data of consciousness, and find reasons among them to support his inferences to – or, more generally, beliefs about – a world outside his head. One of the major shifts in twentieth-century philosophy has been the rejection of this Cartesian assumption. Among the serious difficulties with this assumption is that scepticism becomes impossible either to ignore or refute if we accept it. Another is that on such a thin basis we are simply not entitled to think of the solipsistic would-be knower, alone inside his mind, as capable of naming and thinking about his sensations and experiences, still less as being able to reason from them to an external world. Both thoughts push us firmly towards the thought that the proper place to begin epistemology is, somehow, in the public domain.
    The external world and other minds
    Russell himself was not content with the way he had set out matters in PP , which after all was intended as a popular book and did not offer a rigorous exposition of its theses. Over the next four decades he returned to the problem of knowledge and perception repeatedly. In the years between publication of PP and the outbreak of the First World War he devoted himself seriously to them, drafting his big Theory of Knowledge manuscript, part of which he published and part of which he abandoned, and writing a major series of lectures which appeared in 1914 as Our Knowledge of the External World ( OKEW ). In this work he gives more detailed thought to aspects of the theory in PP , with significant results.
    One difference between the theories of PP and OKEW is that Russell had come to see that the experiencing subject’s basis for knowledge – the sense-data that appear to him alone, and his intuitive knowledge of the laws of logic – is too slender a starting-point. He was not rejecting the Cartesian assumption just discussed; rather, now somewhat more sensitive to the difficulties it poses, he was trying to limit them. He accordingly places greater weight on the subject’s possessing facts of memory, and a grasp of spatial and temporal relations holding among the elements of a current experience. The subject is also empowered to compare data, for example as to