Perceptual knowledge: some problems of knowledge and meaning in later Russell and Nyāya

Abstract

This thesis is concerned with aspects of Russell's theory of knowledge after his conversion, in 1921, to a kind of neutral monism. The particular aspect of Russell's theory of knowledge the thesis examines is his theory of perceptual knowledge and the role perceptual knowledge plays in our knowledge of the physical world. The conclusion is that, for Russell, perceptual knowledge plays a fundamental but limited role in both scientific and everyday knowledge. That is, for Russell, what constitutes knowledge is often the conclusion of non-demonstrable inference, which is based on perceptual knowledge but goes beyond it. Three important consequences follow from Russell's conception of knowledge. Firstly, knowing is largely a private, subjective process which takes place in the mind of the knower. Secondly, knowing is not a matter of certainty but a matter of degrees of probability. Thirdly, it is not possible to validate the sensory core of our perceptual knowledge, on which all our knowledge of the world rests, since percepts are momentary and private events which by definition do not recur. The Nyāya system of Indian philosophy has a very different conception of knowledge from that of Russell. Nyāya does not consider non-perceptual, speculative reasoning, to be knowledge at all. In Nyāya, all knowledge is based ultimately on perceptual experience. The Nyāya theories highlight the essentially subjective nature of knowledge in Russell, the impossibility of validation of mental percepts and the lack of certainty attached to the notion of knowledge in Russell's theory of knowledge. This thesis considers Russell's theories in the following manner: in part 1, perceptual knowledge; in part 2, the verbal expression of our perceptual beliefs; and in part 3, the relation between the sentences expressing our perceptual beliefs and the facts which make those sentences true and the relation of truth to knowledge. Relevant doctrines of the Nyāya system are compared with Russell's theories in order to bring out the implications and presuppositions of Russell's theories.