II. Logic as the Essence of Philosophy. III. On our Knowledge of the External World. IV. The World of Physics and the World of Sense. V. The Theory of Continuity. Free kindle book and epub digitized and proofread by Project Gutenberg. BERTRAND RUSSELL. OUR KNOWLEDGE. OF THE. EXTERNAL WORLD. AS A FIELD FOR SCIENTIFIC. METHOD IN PHILOSOPHY. GEORGE ALLEN & U.
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Newton and Maxwell were the repre- sentative oracles of this worldview, the dominant notions in which were "particle", "field" and "deterministic causality".
As soon as this marvelous architecture was complete, the new tenants found imperfections in it. Almost at the very beginning of the 20th century, Albert Einstein became the author of complaints against the classical theory and leader of the revolution that would rectify its faults. With his theories of special and gene- ral relativity and his conception of the light quantum, based upon fluctuations in kinetic theory and radiation, Einstein created a new vision of the macroscopic and microscopic universe.
Hei- senberg's uncertainty principle and BOhr's principle of complemen- tarity, together with Born's statistical interpretation of the wa- ve function giving rise to statistical as against deterministic causality became the paramount philisophical basis of the under- standing of microscopic phenomena, finding a unified description of nature in the so-called Copenhagen interpretation of quantum mechanics.
The essence of Bohr's principle of complementarity lies in the non-vanishing character of Planck's constant and the existence of Heisenberg's uncertainty principle: The notion of statistical causality, the fundamental notion of chance in the occurrences of nature, led to serious and prolon- ged debates about the new worldview.
Eminent physicists took oppo- site sides: Niels Bohr became the champion of the new quantum mechanics with its statistical interpretation, in which the role of chance and the intermingling of the subject and the object were the essence of the description of nature, while Albert Einstein adhered to the view that such a game of dice is for the Devil and the Creator has a more exact and rational design, and it is the physicist's business to find a "complete" description of physical reality.
In spite of the quantum revolution which Einstein, more than anyone else, had wrought, he expressed faith in a deterministic description of nature that the "final" theory must have - there had to be a one to one correspondence between the elements of phy- sical reality and the mathematical formalism of the theory.
Einstein was convinced that quantum mechanics is "a brilliant shortcut which successfully avoids many of the difficulties and the hard work which the final correct field theory must solve. There is a special section in the purgatory for professors of quantum theory, where they will be obliged to listen to lectures on classical physics ten hours every day.
Who knows who would have the laugh in a few years? On BOhr's side were most of the principal architects of quantum mechanics and the adherents of the Copenhagener Geist der Quantentheorie. Among the major physicists who shared Einstein's concern were Planck, Schrodinger and de Broglie.
Whether Schrodin- ger's cat was dead or alive in an intricately designed experiment also became a celebrated issue in determining the legitimacy of the quantum mechanical explanation. Beginning in the early s, numerous natural philosophers, most prominent among them Eugene Wigner, entered the discussion about the interpretation and epistemology of quantum mechanics and the description of physical reality.
The discussion goes on, and an entire field has been growing up concerned with the mathemati- cal and interpretative foundations of quantum mechanics that seeks to understand the problem of measurement, the role of the observer and the observed, and how completely the "reality" of nature is described by the mathematical structure.
For the first time in physical theory, human consciousness has become an issue, and Wi- gner has even called a "friend" in aid to describe the complete- ness of the process of measurement.
Jauch has devoted his professional scientific career to the cleaning up of the mathematical structure of quantum mechanics, appealing to the highest standards of purity and rigor.
He has created a flourishing school at Geneva devoted to clarifying all problems that arise in the mathematical formalism of quantum mechanics, and his band of disciples and collaborators range far and wide on the globe. Since he has also played an active and passionate role in discus- sions about the problem of measurement and the interpretation of quantum mechanics. In Are Quanta Real? The three interlocutors in the dialogue are again Salviati, Sagredo and Simplicio, the principals in Galileo's dialogue on the Two Major Systems of the World, meeting again since the end of the fourth day of their last dialogue in That Jauch should have chosen to bring Salviati, Sagredo and Simplicio together for a new dialogue and to become its recorder is not accidental.
What better than that the three old Venetian friends should meet again for rational inquiry within walking distance of the Reformation Wall, away from the shadows of theological super- stition and tyranny?
Salviati declares the purpose of their new encounter. It is to discourse "as distinctly and concretely as possible on the na- tural reasons hitherto alleged on one side by those who maintain deterministic, materialistic philosophy, and on the other by the followers of the Copenhagen interpretation of quantum mechanics.
Jauch, "Are Quanta Real? Simplicio expresses his belief that the reality of the objec- tive world is not only common senses but can be proved logically "with the most subtle of reasons and by experimentation". Sagredo cautions his friends not to rush to conclusions. The discussion is joined and continues in sessions spread over four days, Sagredo preserving a subtle neutrality and trying to bring together the opposites. Salviati gives an example of the situation which would reveal the complementarity of certain physical properties, by considering the observation of a source of light through two sheets of pola- roid.
As one of the sheets is rotated with respect to the first, the intensity of light goes from a maximum to a minimum and to a maximum again. This remarkable behavior is discussed from the points of view of Aristotle and Democritos, Fresnel and Maxwell, electromagnetic waves and photons.
He does not know, as Salviati points out, that a theory which can be made to agree with all possible observable facts is no theory at all. Says Salviati knowingly: The bold and courageous ideas of the nonconformists have always represented the milestones of progress in science.
Salviati points out that even in the classical realm strict causality or determinism cannot be proved in all circumstances. Simplicio appeals to the wisdom of the fundamental truth that "all events in nature are internally connected, and that it is incorrect to consider things and events as separated from one ano- ther". In other words, says Simplicio, "There are no separate phe- nomena, but every phenomenon preceived individually belongs to a whole into which it is integrated.
Bohr's principle of complementarity is discussed as "one of the greatest discoveries in the scientific history of mankind, with ramifications on many other levels of science". Why do we have two hands and two feet? Why do our eyes see only a tiny fraction of the spectrum? In modern logic. In that logic. There is no objective fact it leads his bed" to which hension. Charles I and death and his but they are not.
If all judgments were true. The case of judgment demands the admission of more complicated forms. In this respect it is the exact opposite of the logic practised by the classical tradition.
But to absolutely insoluble difficulties in the case of error. And where a may solution appears possible. Berkeley brings several weapons. The mystic. Every one of these lines of attack raises vital and interesting problems. This line of argument will be developed in the present lecture.
But it would be a mistake to infer that they are dependent upon mind. I think it must be admitted as probable that the imme- diate objects of sense depend for their existence upon physiological conditions in ourselves. If we attempted to deal fully with this logic. The logic of the idealist tradition has gradually grown very complex and very abstruse.
In our last lecture. In this lecture. In every philosophical problem. In the. I wish to apply the logical-analytic method to one of the oldest problems of philosophy. What I have to say on this problem does not amount to an answer of a definite and dogmatic kind it amounts only to an analysis and statement of the questions involved. Our The instrument second lecture has given a short account of modern from the various logic and of its points of divergence traditional kinds of logic.
But although not yet a definite solution. And lastly. Then there is the extension of such particular knowledge to particular things outside our personal experience. In a sense this is true. There is first our acquaintance with particular objects of daily life furniture. It may be said and this be met at the outset that is an objection which must it is the duty of the philo- sopher to call in question the admittedly fallible beliefs of daily life.
But and a very important one. In the main. That is to say. What does not go beyond our own personal sensible the acquaintance must be for us the most certain " " evidence of the senses is proverbially the least open to question. The reason for this abstention from a universal criticism is not any dogmatic confidence. Doubts as to the existence of Napoleon can only be maintained for a joke.
Although data can only be criticized by other data. Universal scepticism. What depends on testimony. In science. These varying degrees of certainty attaching to different data may be regarded as themselves forming part of our data. The first thing that appears when we begin to analyse our common knowledge is that some of it is derivative.
For instance. The law of gravitation. When we hear a person speaking. This applies especially in regard to our space-perceptions. It is obvious that the senses give knowledge of the latter kind: Thus the first step in the analysis of data. We so long as its existence is realized. There may or may not be a possible deduction leading to the same result.
The next step in our analysis must be the consideration of how the derivative parts of our common knowledge arise. We do logical process. If we call a belief logically primitive" when it is not actually arrived at by a logical inference. Here we become involved in a some. The men they persist except a few but it is not psychophilosophers. When we reflect upon the beliefs which axe logically but not psychologically primitive.
We do not feel this as regards the immediate objects of sense: This distinction is not be pressed. There is no accordingly more need of justifying our psychologically derivative beliefs than of justifying those that are primitive. We are thus led to a between what we may somewhat vague distinction " " " hard data and soft " a matter of degree.
We naturally believe. I mean by data those which resist the solvent influence of critical. I do not wish for a moment to maintain that this is certainly not the case. As soon as the question is seriously raised whether. The more we reflect upon these.
If we are to continue philosophizing. At any rate. They may be found. As data.
Real doubt. Without this assumption. The hardest of hard data are of two the particular facts of sense. Applying our distinction of "hard" and "soft" data to psychologically derivative but logically primitive beliefs. Our data now are primarily the facts of sense i. Certain from hard data.
And facts of sense themselves must. But even the severest scrutiny will allow some additions to this slender stock. Some facts of memory especially of recent memory seem to have the highest degree of certainty.
Also we must remember that the distinction of hard and soft data is psychological and subjective. And some facts of comparison. Some introspective facts are as certain as any facts of sense. Such also is the belief in other people's minds this belief is psychologically derivative from our perception of their bodies. For the present. The best we can say for it is that it is slightly more extensive than the world at which Descartes arrived by a similar Belief in what process.
It seems probable that distances. We are now in a position to understand and state the problem of our knowledge of the external world. The immediately given world is spatial. The problem Can the existence of anything other really is than our own hard data be inferred from the But before considering existence of those data?
The existence of a book. Among many other things which we may mean by the Self. The second is: Thus in this sense " Can we know of the existence of any the question. Another form in which the question is often put is " Can we know of the existence of any reality which is " This form of the question independent of ourselves? The bare subject. The only way. When we say that one thing is " independent " of another.
Our question in the above form raises two distinct problems. This form. The question of causal dependence is much more To know that one kind of thing is causally difficult. If this is the case. But in the case of objects of sense this is not obvious indeed. We will consider this latter problem first. If this distinction is made. If it is not valid. For reasons explained in The Analysis of Mind e. But it will not it is be necessary to assume the correctness of in what this view follows.
I have come to regard the distinction as not valid. According to some authors among whom I was formerly included it is necessary to distinguish between a sensation.
I mean is just that patch of colour which is momentarily seen when we look at the table. Both the thing-in-itself of philosophy and the matter of physics present themselves as causes of the sensible object as much as of the sensation.
This latter problem arises " in philosophy as the problem of the thing in itself. What we ought to say is that. A table viewed from one place presents a different appearance from that which it presents from another This is the language of common sense. Let us try to state what is known in terms of sensible objects alone. But in speaking of walking round the table. It is extraordinarily difficult to see just what the arguments prove.
In each case. But there are arguments against this view. At first. We find that as we walk round the table. All these operations. More altering its appearance. What is really known is a correlation of muscular and other bodily sensations with changes in visual sensations. Let us take the case of the blue spectacles. But walking round the table is not the only We way of can shut one eye.
Thus the discovery that the intervening medium affects the appearances of things cannot be made by means of the sense of sight alone. Anything intervening between ourselves and what we see must be invisible our view in every direction is bounded by the nearest visible object.
It is not quite so easy as in the former case to reduce this set of facts to a form in which nothing is assumed beyond sensible objects. Physiological changes also we alter the appearances of things. This is what we really know by experience. But in this case we really see a spotted patchwork the dirtier specks in the glass are visible.
It might be objected that a dirty pane of glass. If we assume the world of common sense. When it has been accomplished. We have fallen into the assumption that the object of which we are conscious when we touch the blue spectacles So still exists after we have ceased to touch them.
We may say that the. The glass itself is known by means of the sense of touch. This correlation when stated by no means a itself. In order to know that The frame blue glass. If we are to account for the blue appearance of objects other than the spectacles. It may be questioned. The blueness.
It may be said that our hypothesis is useless in the case when the blue glass is never touched at all. All that we touch is really known is that the visual appearance in question. Must not these be attributed to permanent possession. And more generally. It is often supposed that nothing which has ceased to exist can continue to have effects. Let us consider the more general question first. But the mere fact that we are able to infer what our tactile sensations would be shows that it is not logically necessary to assume tactile qualities before they are felt.
In this view. Experience has taught us that where we see certain we can. If touch-space. By objects at the times when they and of touch sensacorrelation the of sight experience tions. I think it may be laid down quite generally that. If we are to avoid non-sensible objects.
But in such a case as that of the blue spectacles. Now if an expected sense- datum constitutes a verification. Verification consists always in the occurrence of an Astronomers tell us there expected sense-datum. If at the same time. There is in fact a certain regularity or conformity to law about the occurrence of sense-data. If I look at the moon and immediately afterwards hear a train coming. It must be remembered that. But the degree of verification obtainable in this way is very small.
The problem is the existence of anything other than our own hard data be inferred from these data?
We will consider the legitimacy of this belief presently for the moment. The verifica- tion of physics which is possible at our present level is. I only wish to point out that it needs the same kind of justification as our belief that the moon exists when we do not see it.
When we his toe. This fact. The assumption that sensible objects persist after they have ceased to be sensible for example. What we then find. I hope. The thing-in-itself.
The first thing to realize is that there are no such. It is supposed that the table for example causes our sense-data of sight and touch. Although we cannot rest content with the above theory.
The objection to this theory. But what remains far from dear is the nature of the sensation. Let us see how this is to be done. But before examining the question of our knowledge of other minds. Dreams and waking life. Accepting the indubitable momentary reality of objects of sense. If we It see two tables. If aspects can all really we press one eyeball.
Merely the unusual nature of their connection with other objects of sense. Objects of sense are " " called real when they have the kind of connection with other objects of sense which experience has led us that I 1 to regard as normal " called illusions. I dream am in America. But all that we are warranted in saying is that. When all are changed by a bodily movement. Let us imagine that each mind looks out upon the world.
Thus the difficulty. The use of such a phrase presupposes that all our difficulties have been solved. Each mind sees at each moment an immensely complex three-dimensional world is seen.
It may be possible to pare away what is our hypothesis. We will now make a new start. This makes us declare the two visual tables an illusion. Two men are sometimes found to perceive very similar perspectives. I shall call the system of "perspectives" " " to I shall confine the expression private worlds such views of the universe as are actually perceived.
The system consisting of all views of the universe. They say they see. We may further suppose that there are an infinite number of such worlds which are in fact unperceived. Hence we may suppose. If two men are sitting in a room. It is a relation between the perspectives. All the aspects of a are real. It has. In case the similarity is very great. Given an object in one perspective.
We can and now least if we choose three-dimensional. The correlation of the times of By different perspectives raises certain complications. They are ordered by means of their similarities. There axe as many private spaces as there are perspectives. We can then form a whole series of perspectives containing a gradu- ated series of circular aspects of varying sizes for this purpose we only have to move as we say towards the penny or away from it.
It will be observed that. The perspectives in which the penny looks circular will be said to lie on a straight: These two lines will meet in a certain place in perspective space. It is to be remarked " " than our penny might also that any other thing have been chosen to define the relations of our perspectives in perspective space. We can form another straight line of perspectives in which the penny is seen end-on and looks like a straight line of a certain thickness.
We formed a straight line of perspectives in which the penny looked circular. The above is. We can now also explain the correlation between a private space and parts of perspective space. This will be. We can also understand what is meant by saying that our private world is inside our head. It and it assumes that we can remove the penny without being disturbed by any simultaneous changes in the positions of other things. Thus We we can now understand what is meant by speaking of " a thing as near to or far from here.
There will then be just one perspective in which one of the new pennies looks circular and the other straight. But it is plain that such niceties cannot affect the principle. If there a given thing in a certain private space. Having now defined the perspective. The two places associated with a single private world: The laws according to which they change cannot be stated if we only take account of the aspects that are near the thing. The place " at which is the place of the thing to which the aspect " " the is the place of the place from which belongs perspective to which the aspect belongs.
The physicist naturally classifies aspects in the first way. We have now constructed a largely hypothetical picture of the world.
It will be observed that two places in perspective space are associated with every aspect of a thing: Let us now endeavour to state the fact that the aspect which a thing presents at a given place is affected by the intervening medium. The aspects of a thing in different perspectives are to be conceived as spreading outwards from the place where the thing is. Every aspect of a thing is a member of two different classes of aspects. This empirical fact can. The world we have constructed can.
We will resume this inquiry by taking up again the question of testimony and the evidence for the existence that of other minds. It fits the facts. And yet. What we have derived from our hypothetical construction is that there are no grounds against the truth of this belief. It will give unexpected answers. It must be conceded to begin with that the argument in favour of the existence of other people's minds cannot be conclusive.
But this whole scene. Other people's bodies behave as ours do when influence we have analogy. This may be true. The obvious argument is. Is there any logical ground Or? The minds of other people are among our data. Is there anything to make the argument from analogy more cogent when we are is Someone says we think awake? The analogy in waking 1 as life is only to be preferred to. The natural hypothesis would be that demons and the spirits of the dead visit us while we sleep. There is therefore nothing to be said against its truth.
At the same time. Certain uniformities are observed in waking life. It is only the failure of our dreams to form a consistent whole either with each other or with waking life that makes us condemn them. On the If ' other hand. Who shall condemn him Or who shall justify the shall justify him? Who seeming we sup- hypothesis that other people have minds must. Our hypothetical construction meets these arguments. Probably the construction is only in part necessary as an initial.
And if it is justified. This somewhat meagre conclusion must not be regarded as the whole outcome of our long discussion.
The problem of the connection of sense with objective reality has commonly been dealt with from a standpoint which did not carry initial doubt so far as we have carried it. It is this hypothetical construction. Their difficulties have arisen after this admission. Such difficulties have made people doubtful how far objective reality could be known by sense at all. Men of science. All that I can hope to do is to make the problem felt.
It is therefore necessary to find some way of bridging the gulf between the world of physics and the world of sense. The problem is difficult. But such an attitude. Physicists appear to be unconscious of the gulf. Physics started from the common-sense belief in fairly permanent and fairly. Such objects were peculiar in the fact that they seemed to disappear completely.
This problem. But tables and chairs. Then there are other things. This common-sense belief. The modern form of atomism regards all matter two kinds of units. Thus the and absolutely permanent which early physicists pursued throughout the changing appearances. Here the " indivisible unit is a unit of action. A but the powder consists of grains which retain the character they had before the pounding.
Apart from the special form of the atomic theory which was invented for the needs of chemistry. Ice and snow. Solid bodies. This billiard-ball view of matter dominated the imagination of physicists until ideal of absolutely rigid bodies. While engaged in the necessary logical constructions. Experience teaches us to obtain one space from these by correlation.
In the world of immediate data nothing is pereasier it physics to sense-data. The construction of a single time offers less difficulty so long as we confine ourselves to one person's private world. In attempting to construct them from sense-data and particulars structurally analogous to sense-data. But before doing so. Relativity has introduced a wholly novel analysis of physical concepts. So far from one all.
Philosophical writers on physics sometimes speak as though the conservation of something or other were essential to the possibility of science. Why should we suppose that. One task. This belief was. What we really know is that. On the contrary. If the a priori belief in permanence had not existed. We can give laws according to which the one appearance will be succeeded by the other.
Merely because this supposition enables us to state the phenomena in a way which is consonant with our prejudices. It is of course the in fades years. Thus a thing may be defined as a certain series of appearances.
We say. What this means is that. The time has hardly come when we can state precisely what this legitimate conception is. In the case of slowly a changing things. But what do we really know about it? More generally. The above extrusion of permanent things affords an example of the maxim which inspires all scientific " " Occam's razor Entities are philosophizing. Very often the resulting statement is more complicated and difficult than one which.
We find it easier to imagine a wall-paper with changing colours than to think merely of the series of colours. Everything will then proceed as before whatever was verifiable is unchanged. In other words. These are collected together by the of its aspects. To common sense. In these cases. A rough and approximate answer to this question There are certain fairly stable is not very difficult.
Another insufficient criterion of one thing is continuity. As we have already seen. And so it comes to be is necessary and thought that continuity of change 8. This conflict. In this hypothetical sense. Thus something more must be sought before we can give even the roughest definition of a " thing.
The utmost we can say is that discontinuity during uninterrupted observation is as a rule a mark of difference between things.
Continuity is also not sufficient. Whitehead , to whom are due almost all the differences between the views advocated here and those suggested in The Problems of Philosophy. What is said on these topics here is, in fact, a rough preliminary account of the more precise results which he is giving in the fourth volume of our Principia Mathematica. The speculations of the past as to the reality or unreality of the world of physics were baffled, at the outset, by the absence of any satisfactory theory of the mathematical infinite.
This difficulty has been removed by the work of Georg Cantor. But the positive and detailed solution of the problem by means of mathematical constructions based upon sensible objects as data has only been rendered possible by the growth of mathematical logic, without which it is practically impossible to manipulate ideas of the requisite abstractness and complexity. This aspect, which is somewhat obscured in a merely popular outline such as is contained in the following lectures, will become plain as soon as Dr.
In pure logic, which, however, will be very briefly discussed in these lectures, I have had the benefit of vitally important discoveries, not yet published, by my friend Mr. Ludwig Wittgenstein. Since my purpose was to illustrate method, I have included much that is tentative and incomplete, for it is not by the study of finished structures alone that the manner of construction can be learnt. This work is in the public domain in the United States because it was published before January 1, The author died in , so this work is also in the public domain in countries and areas where the copyright term is the author's life plus 30 years or less.
This work may also be in the public domain in countries and areas with longer native copyright terms that apply the rule of the shorter term to foreign works.