Human Knowledge: Its Scope and Limits

Bertrand Russell

• Publisher: Routledge
• Year: 2009
• ISBN:
  9781134026210
• Edition: 1
• Topic: Philosophy
• Subtopic: Philosophy History & Theory

How do we know what we "know"? How did we –as individuals and as a society – come to accept certain knowledge as fact? In Human Knowledge, Bertrand Russell questions the reliability of our assumptions on knowledge. This brilliant and controversial work investigates the relationship between 'individual' and 'scientific' knowledge. First published in 1948, this provocative work contributed significantly to an explosive intellectual discourse that continues to this day.

Part I

The World of Science

1

INDIVIDUAL AND SOCIAL KNOWLEDGE

Scientific knowledge aims at being wholly impersonal, and tries to state what has been discovered by the collective intellect of mankind. In this chapter I shall consider how far it succeeds in this aim, and what elements of individual knowledge have to be sacrificed in order to achieve the measure of success that is possible.

The community knows both more and less than the individual: it knows, in its collective capacity, all the contents of the Encyclopaedia and all the contributions to the Proceedings of learned bodies, but it does not know the warm and intimate things that make up the colour and texture of an individual life. When a man says “I can never convey the horror I felt on seeing Buchenwald” or “no words can express my joy at seeing the sea again after years in a prison camp”, he is saying something which is strictly and precisely true: he possesses, through his experience, knowledge not possessed by those whose experience has been different, and not completely capable of verbal expression. If he is a superb literary artist he may create in sensitive readers a state of mind not wholly unlike his own, but if he tries scientific methods the stream of his experience will be lost and dissipated in a dusty desert.

Language, our sole means of communicating scientific knowledge, is essentially social in its origin and in its main functions. It is true that, if a mathematician were wrecked on a desert island with a note-book and a pencil, he would, in all likelihood, seek to make his solitude endurable by calculations using the language of mathematics; it is true also that a man may keep a diary which he intends to conceal from all eyes but his own. On a more everyday plane, most of us use words in solitary thinking. Nevertheless the chief purpose of language is communication, and to serve this purpose it must be public, not a private dialect invented by the speaker. It follows that what is most personal in each individual's experience tends to evaporate during the process of translation into language. What is more, the very publicity of language is in large part a delusion. A given form of words will usually be interpreted by competent hearers in such a way as to be true for all of them or false for all of them, but in spite of this it will not have the same meaning for all of them. Differences which do not affect the truth or falsehood of a statement are usually of little practical importance, and are therefore ignored, with the result that we all believe our private world to be much more like the public world than it really is.

This is easily proved by considering the process of learning to understand language. There are two ways of getting to know what a word means: one is by a definition in terms of other words, which is called verbal definition; the other is by frequently hearing the word when the object which it denotes is present, which is called ostensive definition. It is obvious that ostensive definition is alone possible in the beginning, since verbal definition presupposes a knowledge of the words used in the definiens. You can learn by a verbal definition that a pentagon is a plane figure with five sides, but a child does not learn in this way the meaning of every-day words such as “rain”, “sun”, “dinner”, or “bed”. These are taught by using the appropriate word emphatically while the child is noticing the object concerned. Consequently the meaning that the child comes to attach to the word is a product of his personal experience, and varies according to his circumstances and his sensorium. A child who frequently experiences a mild drizzle will attach a different idea to the word “rain” from that formed by a child who has only experienced tropical torrents. A short-sighted and a long-sighted child will connect different images with the word “bed”.

It is true that education tries to depersonalize language, and with a certain measure of success. “Rain” is no longer the familiar phenomenon, but “drops of water falling from clouds towards the earth”, and “water” is no longer what makes you wet, but H₂O. As for hydrogen and oxygen, they have verbal definitions which have to be learnt by heart; whether you understand them does not matter. And so, as your instruction proceeds, the world of words becomes more and more separated from the world of the senses; you acquire the art of using words correctly, as you might acquire the art of playing the fiddle; in the end you become such a virtuoso in the manipulation of phrases that you need hardly ever remember that words have meanings. You have then become completely a public character, and even your inmost thoughts are suitable for the Encyclopaedia. But you can no longer hope to be a poet, and if you try to be a lover you will find your depersonalized language not very successful in generating the desired emotions. You have sacrificed expression to communication, and what you can communicate turns out to be abstract and dry.

It is an important fact that the nearer we come to the complete abstractness of logic, the less is the unavoidable difference between different people in the meaning attached to a word. I see no reason why there should be any difference at all between two suitably educated persons in the idea conveyed to them by the word “3481”. The words “or” and “not” are capable of having exactly the same meaning for two different logicians. Pure mathematics, throughout, works with concepts which are capable of being completely public and impersonal. The reason is that they derive nothing from the senses, and that the senses are the source of privacy. The body is a sensitive recording instrument, constantly transmitting messages from the outside world; the messages reaching one body are never quite the same as those reaching another, though practical and social exigencies have taught us ways of disregarding the differences between the percepts of neighbouring persons. In constructing physics we have emphasized the spatio-temporal aspect of our perceptions, which is the aspect that is most abstract and most nearly akin to logic and mathematics. This we have done in the pursuit of publicity, in order to communicate what is communicable and to cover up the rest in a dark mantle of oblivion.

Space and time, however, as human beings know them, are not in reality so impersonal as science pretends. Theologians conceive God as viewing both space and time from without, impartially, and with a uniform awareness of the whole; science tries to imitate this impartiality with some apparent success, but the success is in part illusory. Human beings differ from the theologians’ God in the fact that their space and time have a here and now. What is here and now is vivid, what is remote has a gradually increasing dimness. All our knowledge of events radiates from a space–time centre, which is the little region that we are occupying at the moment. “Here” is a vague term: in astronomical cosmology the Milky Way may count as “here”, in the study of the Milky Way “here” is the solar system, in the study of the solar system “here” is the earth, in geography it is the town or district in which we live, in physiological studies of sensation it is the brain as opposed to the rest of the body. Larger “heres” always contain smaller ones as parts; all “heres” contain the brain of the speaker, or part of it. Similar considerations apply to “now”.

Science professes to eliminate “here” and “now”. When some event occurs on the earth's surface, we give its position in the space–time manifold by assigning latitude, longitude, and date. We have developed a technique which insures that all accurate observers with accurate instruments will arrive at the same estimate of latitude, longitude, and date. Consequently there is no longer anything personal in these estimates, in so far as we are content with numerical statements of which the meaning is not too closely investigated. Having arbitrarily decided that the longitude of Greenwich and the latitude of the equator are to be zero, other latitudes and longitudes follow. But what is “Greenwich”? This is hardly the sort of term that ought to occur in an impartial survey of the universe, and its definition is not mathematical. The best way to define “Greenwich” is to take a man to it and say: “Here is Greenwich.” If some one else has already determined the latitude and longitude of the place where you are, “Greenwich” can be defined by its latitude and longitude relative to that place; it is, for example, so many degrees east and so many degrees north of New York. But this does not get rid of “here”, which is now New York instead of Greenwich.

Moreover it is absurd to define either Greenwich or New York by its latitude and longitude. Greenwich is an actual place, inhabited by actual people, and containing buildings which antedate its longitudinal pre-eminence. You can, of course, describe Greenwich, but there always might be another town with the same characteristics. If you want to be sure that your description applies to no other place, the only way is to mention its relation to some other place, for instance, by saying that it is so many miles down the Thames from London Bridge. But then you will have to define “London Bridge”. Sooner or later you are faced with the necessity of defining some place as “here”, and this is an egocentric definition, since the place in question is not “here” for everybody. There may be a way of escape from this conclusion; at a later stage, we will resume the question. But there is no obvious or easy way of escape, and until one is found all determinations of latitude and longitude are infected with the subjectivity of “here”. This means that, although different people assign the same latitude and longitude to a place, they do not, in ultimate analysis, attach the same meaning to the figures at which they arrive.

The common world in which we believe ourselves to live is a construction, partly scientific, partly pre-scientific. We perceive tables as circular or rectangular, in spite of the fact that a painter, to reproduce their appearance, has to paint ellipses or non-rectangular quadrilaterals. We see a person as of about the same size whether he is two feet from us or twelve. Until our attention is drawn to the facts, we are quite unconscious of the corrections that experience has led us to make in interpreting sensible appearances. There is a long journey from the child who draws two eyes in a profile to the physicist who talks of electrons and protons, but throughout this journey there is one constant purpose: to eliminate the subjectivity of sensation, and substitute a kind of knowledge which can be the same for all percipients. Gradually the difference between what is sensed and what is believed to be objective grows greater; the child's profile with two eyes is still very like what is seen, but the electrons and protons have only a remote resemblance of logical structure. The electrons and protons, however, have the merit that they may be what actually exists where there are no sense-organs, whereas our immediate visual data, owing to their subjectivity, are almost certainly not what takes place in the physical objects that we are said to see.

The electrons and protons—assuming it scientifically correct to believe in them—do not depend for their existence upon being perceived; on the contrary, there is every reason to believe that they existed for countless ages before there were any percipients in the universe. But although perception is not needed for their existence, it is needed to give us a reason for believing in their existence. Hundreds of thousands of years ago, a vast and remote region emitted incredible numbers of photons, which wandered through the universe in all directions. At last a very few of them hit a photographic plate, in which they caused chemical changes which made parts of the plate look black instead of white when examined by an astronomer. This tiny effect upon a minute but highly educated organism is our only reason for believing in the existence of a nebula comparable in size with the Milky Way. The order for knowledge is the inverse of the causal order. In the order for knowledge, what comes first is the brief subjective experience of the astronomer looking at a pattern of black and white, and what comes last is the nebula, vast, remote, and belonging to the distant past.

In considering the reasons for believing in any empirical statement, we cannot escape from perception with all its personal limitations. How far the information which we obtain from this tainted source can be purified in the filter of scientific method, and emerge resplendently godlike in its impartiality, is a difficult question, with which we shall be much concerned. But there is one thing that is obvious from the start: only in so far as the initial perceptual datum is trustworthy can there be any reason for accepting the vast cosmic edifice of inference which is based upon it.

I am not suggesting that the initial perceptual datum must be accepted as indubitable; that is by no means the case. There are well-known methods of strengthening or weakening the force of individual testimony; certain methods are used in the law courts, somewhat different ones are used in science. But all depend upon the principle that some weight is to be attached to every piece of testimony, for it is only in virtue of this principle that a number of concordant testimonies are held to give a high probability. Individual percepts are the basis of all our knowledge, and no method exists by which we can begin with data which are public to many observers.

2

THE UNIVERSE OF ASTRONOMY

Astronomy is the oldest of the sciences, and the contemplation of the heavens, with their periodic regularities, gave men their first conceptions of natural law. But in spite of its age, astronomy is as vigorous as at any former time, and as important in helping us to form a just estimate of man's position in the universe.

When the Greeks began inventing astronomical hypotheses, the apparent motions of the sun and moon and planets among the fixed stars had already been observed for thousands of years by the Babylonians and Egyptians, who had also learned to predict lunar eclipses with certainty and solar eclipses with a considerable risk of error. The Greeks, like other ancient nations, believed the heavenly bodies to be gods, or at any rate each closely controlled by its own god or goddess. Some, it is true, questioned this opinion: Anaxagoras, in the time of Pericles, maintained that the sun was a red-hot stone and that the moon was made of earth. But for this opinion he was prosecuted and compelled to fly from Athens. It is very questionable whether either Plato or Aristotle was equally rationalistic. But it was not the most rationalistic among the Greeks who were the best astronomers; it was the Pythagoreans, to whom superstition suggested what happened to be good hypotheses.

The Pythagoreans, towards the end of the fifth century B.c., discovered that the earth is spherical; about a hundred years later, Eratosthenes estimated the earth's diameter correctly within about fifty miles. Heraclides of Pontus, during the fourth century, maintained that the earth rotates once a day and that Venus and Mercury describe orbits about the sun. Aristarchus of Samos, in the third century, advocated the complete Copernican system, and worked out a theoretically correct method of estimating the distances of the sun and moon. As regards the sun this result, it is true, was wildly wrong, owing to inaccuracy in his data; but a hundred years later Posidonius made an estimate which was about half of the correct figure. This extraordinarily vigorous advance, however, did not continue, and much of it was forgotten in the general decay of intellectual energy during later antiquity.

The cosmos, as it appears, for instance, in Plotinus, was a cosy and human little abode in comparison with what it has since become. The supreme deity regulated the whole, but each star was a subordinate deity, similar to a human being but in every way nobler and wiser. Plotinus finds fault with the Gnostics for believing that, in the created universe, there is nothing more worthy of admiration than the human soul. The beauty of the heavens, to him, is not only visual, but also moral and intellectual. The sun and moon and planets are exalted spirits, actuated by such motives as appeal to the philosopher in his best moments. He rejects with indignation the morose view of the Gnostics (and later of the Manicheans) that the visible world was created by a wicked Demiurge and must be despised by every aspirant to true virtue. On the contrary, the bright beings that adorn the sky are wise and good, and such as to console the philosopher amid the welter of folly and disaster that was overtaking the Roman Empire.

The medieval Christian cosmos, though less austere than that of the Manicheans, was shorn of some elements of poetic fancy that paganism had preserved to the end. The change, however, was not very great, for angels and archangels more or less took the place of the polytheists’ celestial divinities. Both the scientific and the poetic elements of the medieval cosmos are set forth in Dante's Paradiso; the scientific elements are derived from Aristotle and Ptolemy. The earth is spherical, and at the centre of the universe; Satan is at the centre of the earth, and hell is an inverted cone of which he forms the apex. At the antipodes of Jerusalem is the Mount of Purgatory, at whose summit is the earthly paradise, which is just in contact with the sphere of the moon.

The heavens consist of ten concentric spheres, that of the moon being the lowest. Everything below the moon is subject to corruption and decay; everything from the moon upwards is indestructible. Above the moon, the spheres in their order are those of Mercury, Venus, the Sun, Mars, Jupiter, Saturn and the fixed stars, beyond which is the Primum Mobile. Last of all, above the Primum Mobile, is the Empyrean, which has no motion, and in which there are no times or places. God, the Aristotelian Unmoved Mover, causes the rotation of the Primum Mobile, which, in turn, communicates its motion to the sphere of the fixed stars, and so on downwards to the sphere of the moon. Nothing is said in Dante as to the sizes of the various spheres, but he is able to traverse them all in the space of twenty-four hours. Clearly the universe as he conceived it was somewhat minute by modern standards; it was also very recent, having been created a few thousand years ago. The spheres, which all had the earth at the centr...

Table of contents

• Front Cover
• Human Knowledge
• Title Page
• Copyright
• CONTENTS
• INTRODUCTION BY JOHN G. SLATER
• PREFACE
• INTRODUCTION
• PART I The World of Science
• PART II Language
• PART III Science and Perception
• PART IV Scientific Concepts
• PART V Probability
• PART VI Postulates of Scientific Inference
• INDEX