Russell - A Very Short Indroduction (9 page)

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 differences of colour and shape. Ordinary common beliefs, and belief in the existence of other minds, are still excluded.

With this enriched basis of what he now calls ‘hard data’, Russell formulates the question to be answered thus; ‘can the existence of anything other than our own hard data be inferred?’ His approach is first to show how we can construct, as a hypothesis, a notion of space into which the facts of experience – both the subject’s own and those he learns by the testimony of others – can be placed. Then, to see whether we have reason for believing that this spatial world is real, Russell gives an argument for believing that other minds exist, because if one is indeed entitled to believe this, then one can rely on the testimony of others, which, jointly with one’s own experience, will give powerful support to the view that there is a spatial – that is, a real – world.

This strategy is ingenious. In the paper ‘The Relation of Sense-Data to Physics’, written in early 1914, Russell adds to it an equally ingenious way of thinking about the relation of sense-experience to things. In
PP
he had said that we infer the existence of physical things from our sensedata; now he describes them as functions of sense-data, or as he sometimes puts it, ‘constructions’ out of sense-data. This employs the technique of logic in which one thing can be shown to be analysable into things of another kind. Russell describes as the ‘supreme maxim of scientific philosophising’ the principle that ‘wherever possible, logical constructions are to be substituted for inferred entities’. In accordance with this principle, physical objects are accordingly to be analysed as constructions out of sense-data; yet not out of actual or occurrent sense-data only, but out of ‘sensibilia’ also, by which is meant ‘appearances or, in Russell’s phrase, ‘how things appear’, irrespective of whether they constitute sense-data which are currently part of any perceiver’s experience. This is intended to explain what it is for an object to exist when not being perceived.

An important aspect of this view is, Russell now holds, that sense-data and sensibilia are not private mental entities, but part of the actual subject-matter of physics. They are indeed ‘the ultimate constituents of the physical world’, because it is in terms of them that verification of common sense and physics ultimately depends. This is important because we usually think that sense-data are functions of physical objects, that is, exist and have their nature because physical objects cause them; but verification is only possible if matters are the other way round, with physical objects as functions of sense-data. This theory ‘constructs’ physical objects out of sensibilia; the existence of these latter therefore verifies the existence of the former.
Instead of developing this distinctive theory further, Russell abandoned it; in later work, particularly in
The Analysis of Matter
(
AMt
) in 1927 and
Human Knowledge
(
HK
) in 1948, he reverted to treating physical objects, and the space they occupy, as inferred from sense-experience. A number of considerations made him do this. One was his acceptance, driven by the sciences of physics and human physiology, of the standard view they offer that perception is caused by the action of the physical environment on our sense organs. ‘Whoever accepts the causal theory of perception’, he writes, ‘is compelled to conclude that percepts are in our heads, for they come at the end of a causal chain of physical events leading, spatially, from the object to the brain of the percipient’ (
AMt
32). He also, in
The Analysis of Mind
(
AMd
) in 1921 gave up talk of ‘sensedata’, and ceased to distinguish between the act of sensing and what is sensed. His reason for this relates to his theory of the mind, sketched later.

Another major reason for Russell’s abandonment of the theory was the sheer complexity and, as he came to see it, implausibility of the views he tried to formulate about private and public spaces, the relations between them, and the way sensibilia are supposed to occupy them. He makes a passing mention of this cluster of problems in
MPD
. And he there reports that his main reason for abandoning ‘the attempt to construct “matter” out of experienced data alone’ is that it ‘is an impossible programme . . . physical objects cannot be interpreted as structures composed of elements actually experienced’ (
MPD
79). Now, this last remark is not strictly consistent with Russell’s stated view in the original texts that sensibilia do not have to be actually sensed;
MPD
gives a much more phenomenalistic gloss to the theory than its original statement does. But it touches upon a serious problem with the theory: which is that it seems simply incoherent to speak of an ‘unsensed sensedatum’ that does not even require – as its very name seems
per contra
to demand – an essential connection with perception.

Giving up the project embodied in the
Theory of Knowledge
manuscript and
OKEW
was doubtless a blow to Russell, because when, after finishing
PM
, he turned his attention to questions of knowledge and perception, he saw the task of solving problems about the relation between these matters and physics as his next major contribution. It was an ambition he had nourished since the late 1890s.

There are other important questions in epistemology to which, in these endeavours, Russell gave only passing attention. They concern the kind of reasoning traditionally supposed to be the mainstay of science, namely, non-demonstrative inference. It was some years before Russell returned to consider these questions: the main discussion he gives is to be found in
HK
, written after the Second World War. In the meantime he turned his attention to certain questions of method and metaphysics which, during the course of his work on perception, had come to seem to him important. These questions are the subject of the next chapter.

Chapter 3 Philosophy, mind, and science

Method and metaphysics

Russell gave the name ‘logical atomism’ to the views he developed from
OKEW
onwards. Logical atomism is principally a method, and Russell hoped that it would resolve questions about the nature of perception and its relation to physics. It is important to note that Russell’s philosophical work in the four decades after
Principia Mathematica
is chiefly devoted to the particular question of the relation of perception to physics, and is in effect thus an attempt to provide a (qualified) empirical basis for science, considered as the theory of the world which has the best chance of being true or at least on the way to truth. Logical atomism also thereby gave Russell his metaphysics – that is, his account of the nature of reality – which turns out not to be, at least in a straightforward way, the current physics of matter, but a representation of it as a logical structure. Russell’s accounts of his metaphysical views almost invariably take the form of a sketch occupying the concluding parts of his various discussions of logical analysis; most of his attention is devoted to describing the analytical strategy itself.

The philosophy of logical atomism

Russell describes logical atomism in a number of places, the most important being the chapter in
OKEW
entitled ‘Logic as the Essence of Philosophy’, and the series of lectures delivered in 1918 under the heading ‘The Philosophy of Logical Atomism’ (reprinted in Marsh,
Logic and Knowledge
). There is a summary of logical atomism’s methods and aims in the essay ‘Logical Atomism’ (1924) also reprinted in Marsh.

A key to the method of logical atomism lies in Russell’s claim that ‘logic is the essence of philosophy’, where ‘logic’ means mathematical logic. Its importance is that it provides the means of effecting powerful and philosophically revealing analyses of structures; in particular, the related structures of propositions and facts.

It has already been seen how the analysis of propositions shows that it is a mistake to treat them all as subject-predicate in form, and that in this and related ways surface grammar misleads, as when we take descriptions and ordinary names to be denoting expressions. There is likewise a structure-revealing analysis to be given of the world we talk about when we assert these propositions, and of the propositions themselves.

In ‘Logic as the Essence of Philosophy’ Russell sketches these two related structures by starting with the former. The world, he says, consists of many things with many qualities and relations. An inventory of the world would require not just a list of things, but of things with these qualities and relations – in other words, it would be an inventory of facts. Things, qualities, and relations are the constituents of facts, and facts can in turn be analysed into them. Facts are expressed by what Russell calls ‘propositions’, defined as ‘forms of words asserted as true or false’. Propositions which express basic facts – that is, which simply assert that a thing has a certain quality or stands to some other thing in a certain relation – he calls ‘atomic propositions’. When these are combined by means of logical words such as ‘and’, ‘or’, and ‘if – then’, the result is complex or ‘molecular’ propositions. Such propositions are exceedingly important because all possibility of inference depends upon them.
Finally there are ‘general propositions’ such as ‘all men are mortal’ (and their denials, formed with the word ‘some’ as in ‘some men are not mortal’). The facts they express depend to some degree upon a priori knowledge. This crucial point emerges as a result of reflection upon the analysis of propositions and facts. Theoretically, if we knew all the atomic facts, and that they are
all
the atomic facts, we could infer all other truths from them. But general propositions cannot be known by inference from atomic facts alone. Consider ‘all men are mortal’: if we knew each individual man and his mortality, we still could not infer that all men are mortal until we knew that these were all the men there are; and this is a general proposition. Russell was keen to stress the importance of this point. Because general truths cannot be inferred from particular truths alone, and because all empirical evidence is of particular truths, it follows that there must be some general a priori knowledge if there is knowledge at all. Russell took this to refute the older empiricists, for whom all knowledge rests solely on sense experience.

The question immediately arises as to where such general knowledge is found. Russell’s answer remains what it had been in
PP
: such knowledge is found in logic, which provides us with completely general self-evident propositions. Consider the proposition, ‘all men are mortal, Socrates is a man, therefore Socrates is mortal’. It contains empirical terms (‘Socrates’, ‘man’, ‘mortal’) and is therefore not a proposition of pure logic. But the proposition of pure logic which represents its form, ‘if anything has a certain property, and whatever has this property has a certain other property, then this thing has this other property’ (clearer still: ‘all Fs are Gs, x is F, therefore x is G’) is both completely general and self-evident. Just such propositions take us beyond the limits of empirical particularity.

In ‘The Philosophy of Logical Atomism’ the details of this analytical programme are spelled out in greater detail. The ‘logical’ in the label signals that the atoms are arrived at as the ‘last residue of analysis’ where the analysis is logical rather than physical (PLA 178). They are particulars such as ‘little patches of colour or sounds, momentary things – and . . . predicates or relations’. The aim is to pass from ordinary beliefs about the world to an accurate grasp of how experience underwrites science; that is, to pass from ‘those obvious, vague, ambiguous things, that we feel quite sure of, to something precise, clear, definite, which by reflection and analysis we find is involved in the vague thing we start from, and is, so to speak, the real truth of which that vague thing is a sort of shadow’ (ibid.). The method is analysis of complex symbols – propositions – into the simple symbols from which they are combined; the terminus of such analysis is ‘direct acquaintance with the objects which are the meanings of [the] simple symbols’ where ‘meaning’ means ‘denotation’ (PLA 194). In a ‘logically perfect language’ such as
Principia Mathematica
is intended to provide, the components of a proposition – the simple symbols – correspond one-toone with the components of a fact, except for the logical expressions ‘or’, ‘and’, and the like. Each simple object is denoted by its own different simple symbol. Such a language, says Russell, shows ‘at a glance the logical structure of the facts asserted or denied’ (PLA 198).