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

was the fact, as it seemed to him, that psychology and physics had come very close: the new physics both of the atom and of relativistic space-time had effectively dematerialized matter, and psychology, especially in the form of behaviourism, had effectively materialized mind. From the internal viewpoint of introspection, mental reality is composed of sensations and images. From the external viewpoint of observation, material things are composed of sensations and sensibilia. A more or less unified theory therefore seems possible by treating the fundamental difference as one of arrangement: a mind is a construction formed of materials organized in one way, a brain more or less the same materials organized in another.
    A striking feature of this view is, surprisingly, how idealist it is. Russell had, as noted, charged James with residual idealism. But here he is arguing something hardly distinguishable: that minds are composed of sensed percepts – namely, sensations and images – and matter is a logical fiction constructed of unsensed percepts. Now Russell had often insisted (using his earlier terminology) that sense-data and sensibilia are ‘physical’ entities, in somewhat the sense in which, if one were talking about an item of sensory information in a nervous system, that datum would be present as impulses in a nerve or activity in a brain. But then nerves and brains, as objects of physical theory, are themselves to be understood as constructions from sensations and sensibilia, not as traditionally understood ‘material substance’, a concept which physics has shown to be untenable. At the end of AMd Russell accordingly says that ‘an ultimate scientific account of what goes on in the world, if it were ascertainable, would resemble psychology rather than physics . . . [because] psychology is nearer to what exists’ ( AMd 305, 308). This explains Russell’s notorious claim that ‘brains consist of thoughts’ and that when a physiologist looks at another person’s brain, what he ‘sees’ is a portion of his own brain (Schilpp, Philosophy of Bertrand Russell , 705).
    For robuster versions of materialism this aspect of Russell’s view is hard to accept. But it is not the only difficulty with his version of neutral monism. Not least is the fact that he failed in his main aim, which was to refute the view that consciousness is essential to the distinction between mental and physical phenomena. He had not of course attempted to analyse consciousness quite away; his aim was rather to reduce its importance for the mind–matter question. But images, feelings, and sensations, which play so central a role in his theory, stubbornly remain conscious phenomena, whereas the sensibilia (by definition often unsensed), which constitute the greater part of matter, are not. Russell accepted this, but tried to specify a criterion of difference which did not trade on these facts, namely, the criterion of membership of different causal realms. But whereas that difference is open to question – and even if it exists might be too often hard to see – the consciousness difference is clear cut.
    Relatedly, the intentionality which characterizes consciousness cannot be left out of accounts of knowledge; memory and perception are inexplicable without it. Russell later acknowledged this point, and gave it as a reason in MPD for having to return to the question of perception and knowledge in later writings.
Russell also later came to abandon the idea – anyway deeply unsatisfactory from the point of view of a theory supposed to be both neutral and monist – that images and feelings are essentially mental, that is, not wholly reducible to neutral stuff; for in a very late essay he says; ‘An event is not rendered either mental or material by any intrinsic quality, but only by its causal relations. It is perfectly possible for an event to have both the causal relations characteristic of physics and those characteristic of psychology. In