Peter Munz on Wittgenstein’s meaning as use

Posted on February 3, 2010 by Matt

The philosophy of late Wittgenstein consisted largely in the contention that the meaning of a sentence consists in its ‘use’. If ‘use’ equals ‘meaning’ then ‘meaning’ equals ‘use’. [footnote omitted] Since all knowledge is a linguistic phenomenon or something expressed in language, Wittgenstein argued, it has to be assessed for validity in the same way in which we assess language. Since there can be no private language — a private language would be a contradiction in terms — all language is a rule-following activity; and the conception ‘rule’ implies that one is behaving in harmony with, and according to, the consensus of other people who form something like a speech community. Wittgenstein summed up this doctrine in his epigram that there is no private language. Though it may seem superficial that this declaration is a declaration in favour of outside reference and against closed circles, it turns out to be the opposite. The easiest way to establish outside reference is by appeal to observation. But since all observation must initially and in the first instance be a private experience and give rise, linguistically, to personal-report sentences, observation must somehow be linked to ‘private language’. The denial that there is such a thing as a private language amounts, therefore, to a denial that one can break out of a closed circle by ‘observing’ what goes on outside. The people who are inside that community are playing a language game. The notion of ‘rule’ rules out the possibility that one is following instructions just once and once only. If one did, one would clearly not be following a ‘rule’. Again, in thus establishing the meaning of a ‘rule’, Wittgenstein is not saying anything of substance, open to a critical test; he is merely drawing our attention to the fact that a ‘rule’ means what the use of the word has in our community and that the meaning of the word ‘rule’ is how the word ‘rule’ is used. There is a vicious circle here, for we find that Wittgenstein’s justification of his declaration that there is no private language depends, in turn, on his insistence that one determines the meaning of words by their use. The validity of the whole argument depends on the validity of the argument. Supposing that the argument is valid, we are then told that when we grasp that there is something which makes a statement true, we derive this grasp from our use of certain basic forms of statements as reports of observation. This situation in which a report is not a report but merely considered a report because there is a rule that it should be, is echoed in a funny scene in Tom Stoppard’s play Jumpers. The hero is conversing with a psychiatrist while his wife in the next room is being interviewed by a detective who is trying to rape her. She cries ‘help!’ and the husband is understandably alarmed. The psychiatrist, however, calms him by saying it means nothing: ‘In the profession, we interpret this sort of cry as a call for help.’ [footnote omitted]

From Knowledge of the Growth of Knowledge, page 141 to 142

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Isaiah Berlin on monism

Posted on February 3, 2010 by Matt

"The enemy of pluralism is monism — the ancient belief that there is a single harmony of truths into which everything, if it is genuine, in the end must fit. The consequence of this belief (which is something different from, but akin to, what Karl Popper called essentialism — to him the root of all evil) is that those who know should command those who do not. Those who know the answers to some of the great problems of mankind must be obeyed, for they alone know how society should be organized, how individual lives should be lived, how culture should be developed. This is the old Platonic belief in the philosopher-kings, who were entitled to give orders to others. There have always been thinkers who hold that if only scientists, or scientifically trained persons, could be put in charge of things, the world would be vastly improved. To this I have to say that no better excuse, or even reason, has ever been propounded for unlimited despotism on the part of an elite which robs the majority of its essential liberties."

For the source of this quote see the selection Isaiah Berlin on Pluralism

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Karl Popper on the scientific status of Darwin’s theory of evolution

Posted on February 3, 2010 by Matt

When speaking here of Darwinism, I shall speak always of today’s theory–that is Darwin’s own theory of natural selection supported by the Mendelian theory of heredity, by the theory of the mutation and recombination of genes in a gene pool, and the decoded genetic code. This is an immensely impressive and powerful theory. The claim that it completely explains evolution is of course a bold claim, and very far from being established. All scientific theories are conjectures, even those that have successfully passed many and varied tests. The Mendelian underpinning of modern Darwinism has been well tested, and so has the theory of evolution which says that all terrestrial life has evolved from a few primitive unicellular organisms, possibly even from one single organism.

However, Darwin’s own most important contribution to the theory of evolution, his theory of natural selection, is difficult to test. There are some tests, even some experimental tests; and in some cases, such as the famous phenomenom known as "industrial melanism", we can observe natural selection happening under our very eyes, as it were. Nevertheless, really severe tests of the theory of natural selection are hard to come by, much more so than tests of otherwise comparable theories in physics or chemistry.

The fact that the theory of natural selection is difficult to test has led some people, anti-Darwinists and even some great Darwinists, to claim that it is a tautology. A tautology like "All tables are tables" is not, of course, testable; nor has it any explanatory power. It is therefore most surprising to hear that some of the greatest contemporary Darwinists themselves formulate the theory in such a way that it amounts to the tautology that those organisms that leave the most offspring leave the most offspring. And C.H. Waddington even says somewhere (and he defends this view in other places) that "Natural selection … turns out … to be a tautology". However, he attributes at the same place to the theory an "enormous power … of explanation". Since the explanatory power of a tautology is obviously zero, something must be wrong here.

Yet similar passages can be found in the works of such great Darwinists as Ronald Fisher, J.B.S. Haldane, and George Gaylord Simpson; and others.

I mention this problem because I too belong among the culprits. Influenced by what these authorities say, I have in the past described the theory as "almost tautological", and I have tried to explain how the theory of natural selection could be untestable (as is a tautology) and yet of great scientific interest. My solution was that the doctrine of natural selection is a most successful metaphysical research programme. It raises detailed problems in many fields, and it tells us what we would expect of an acceptable solution of these problems.

I still believe that natural selection works this way as a research programme. Nevertheless, I have changed my mind about the testability and logical status of the theory of natural selection; and I am glad to have an opportunity to make a recantation. My recantation may, I hope, contribute a little to the understanding of the status of natural selection.

From "Natural Selection and the Emergence of Mind", Dialectica, vol. 32, no. 3-4, 1978, pp. 339-355

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Karl Popper on the importance of grasping the problem situation

Posted on February 3, 2010 by Matt

My second thesis is that what appears to be the prima facie method of teach- ing philosophy is liable to produce a philosophy which answers Wittgenstein’s description. What I mean by ‘prima facie method of teaching philosophy’, and what would seem to be the only method, is that of giving the beginner (whom we take to be unaware of the history of mathematical, cosmological, and other ideas of science as well as of politics) the works of the great philosophers to read; the works, say, of Plato and Aristotle, Descartes and Leibniz, Locke, Berkeley, Hume, Kant and Mill. What is the effect of such a course of reading? A new world of astonishingly subtle and vast abstractions opens itself before the reader; abstractions on an extremely high and difficult level. Thoughts and arguments are put before his mind which sometimes are not only hard to understand, but which seem to him irrelevant because he cannot find out what they may be relevant to. Yet the student knows that these are the great philosophers, that this is the way of philosophy. Thus he will make an effort to adjust his mind to what he believes (mistakenly, as we shall see) to be their way of thinking. He will attempt to speak their queer language, to match the tortuous spirals of their argumentation, and perhaps even tie himself up in their curious knots. Some may learn these tricks in a superficial way, others may begin to become genuinely fascinated addicts. Yet I feel that we ought to respect the man who having made his effort comes ultimately to what may be described as Wittgenstein’s conclusion: ‘I have learned the jargon as well as anybody. It is very clever and captivating. In fact, it is dangerously captivat- ing; for the simple truth about the matter is that it is much ado about nothing –just a lot of nonsense.’

Now I believe such a conclusion to be grossly mistaken; yet it is the almost inescapable outcome, I contend, of the prima facie method of teaching philo- sophy here described. (I do not deny, of course, that some particularly gifted students may find very much more in the works of the great philosophers than this story indicates–and without self-deception.) For the student’s chance of discovering the extra-philosophical problems (mathematical, scientific, moral, and political problems) which inspired these great philosophers is very small indeed. As a rule, these problems can be discovered only by studying the history of, for example, scientific ideas, and especially the problem-situation in mathematics and the sciences during the period in question; and this in turn presupposes a considerable acquaintance with mathematics and science. Only if he understands the contemporary problem-situation in the sciences can the student of the great philosophers understand that they tried to solve urgent and concrete problems; problems which they found could not be dis- missed. And only after understanding this can the student attain a different picture of the great philosophies–one which makes sense of the apparent nonsense.

From, Conjectures and Refutations, pages 72 – 73

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Karl Popper on logic of falsification

Posted on February 3, 2010 by Matt

The falsifying mode of inference here referred to — the way in which the falsification of a conclusion entails the falsification of the system from which it is derived — is the modus tollens of classical logic. It may be described as follows:

Let p be a conclusion of a system t of statements which may consist of theories and initial conditions (for the sake of simplicity I will not distinguish between them). We may then symbolize the relation of derivability (analytical implication) of p from t by ‘t -> p‘ which may be read ‘p follows from t‘. Assume p to be false, which we may write ‘~p‘, to be read ‘not-p’. Given the relation of deducibility, t -> p, and the assumption ~p, we can then infer ~t (read not-t); that is, we regard t as falsified. If we denote the conjunction (simultaneous assertion) of two statements by putting a point between the symbols standing for them, we may also write the falsifying inference thus: ((t->p)•~p)->~t, or in words: ‘If p is derivable from t, and if p is false, then t also is false’

By means of this mode of inference we falsify the whole system (the theory as well as the initial conditions) which was required for the deduction of the statement p, i.e. of the falsified statement. Thus it cannot be asserted of any one statement of the system that it is, or is not, specifically upset by the falsification. Only if p is independent of some part of the system can we say that this part is not involved in the falsification.

From The Logic of Scientific Discovery page 76

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Karl Popper on scientific ethics

Posted on February 3, 2010 by Matt

The hope of getting some argument or theory to share our responsibilities is, I believe, one of the basic motives of ‘scientific’ ethics. ‘Scientific’ ethics is in its absolute barrenness one of the most amazing of social phenomena. What does it aim at? At telling us what we ought to do, i.e. at constructing a code of norms upon a scientific basis, so that we need only look up the index of the code if we are face with a difficult moral decision? This clearly would be absurd; quite apart from the fact that if it could be achieved, it would destroy all personal responsibility and therefore all ethics. Or would it give scientific criteria of the truth and falsity of moral judgments, i.e. of judgments involving such terms as ‘good’ or ‘bad’? But it is clear that moral judgments are absolutely irrelevant. Only a scandalmonger is interested in judging people or their actions; ‘judge not’ appears to some of us one of the fundamental and much too little appreciate laws of humanitarian ethics. (We may have to disarm and to imprison a criminal in order to prevent him from repeating his crimes, but too much of moral judgment and especially of moral indignation is always a sign of hypocrisy and pharisaism.) Thus an ethics of moral judgment would be not only irrelevant but indeed an immoral affair. The all-importance of moral problems rests, of course, on the fact that we can act with intelligent foresight, and that we can ask ourselves what our aims ought to be, i.e. how we ought to act.

Nearly all moral philosophers who have dealt with the problem of how we ought to act (with the possible exception of Kant) have tried to answer it either by reference to ‘human nature’ (as did even Kant, when he referred to human reason) or to the nature of ‘the good’. The first of these ways leads nowhere, since all actions possible to us are founded upon ‘human nature’, so that the problem of ethics could also be put by asking which elements in human nature I ought to approve and to develop, and which sides I ought to suppress or to control. But the second of these ways also leads nowhere; for given an analysis of ‘the good’ in the form of a sentence like: ‘The good is such and such’ (or ‘such and such is good’), we would always have to ask: What about it? Why should this concern me? Only if the word ‘good’ is used in an ethical sense, i.e. only if it is used to mean ‘that which I ought to do’, could I derive from the information ‘x is good’ the conclusion that I ought to do x. In other words, if the word ‘good’ is to have any ethical significance at all, it must be defined as ‘that which I (or we) ought to do (or to promote)’. But if it is so defined, then its whole meaning is exhausted by the defining phrase, and it can in every context be replaced by this phrase, i.e. the introduction of the term ‘good’ cannot materially contribute to our problem. [some reference notes omitted]

All the discussions about the definition of the good, or about the possibility of defining it, are therefore quite useless. They only show how far ‘scientific’ ethics is removed from the urgent problems of moral life. And they thus indicate that ‘scientific’ ethics is a form of escape, and escape from the realities of moral life, i.e. from our moral responsibilities. (In view of these considerations it is not surprising to find that the beginning of ‘scientific’ ethics, in the form of ethical naturalism, coincides in time with what may be called the discovery of personal responsibility. [some reference remarks omitted.]

From The Open Society and Its Enemies (Volume 1), chapter 5, footnote 18

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Karl Popper on moral decision making

Posted on February 2, 2010 by Matt

As we have seen before (in chapter 5), and now again in our analysis of the uncritical version of rationalism, arguments cannot determine such a fundamental moral decision. But this does not imply that our choice cannot be helped by any kind of argument whatever. On the contrary, whenever we are faced with a moral decision of a more abstract kind, it is most helpful to analyse carefully the consequences which are likely to result from the alternatives between which we have to choose. For only if we can visualize these consequences in a concrete and practical way, do we really know what our decision is about; otherwise we decide blindly. In order to illustrate this point, I quote a passage from Shaw’s Saint Joan. The speaker is the Chaplain: he has stubbornly demanded Joan’s death; but when he sees her at the stake, he breaks down; ‘I meant no harm. I did not know what it would be like .. I did not know what I was doing .. If I had known, I would have torn her from their hands. You don’t know. You haven’t seen: it is so easy to talk when you don’t know. You madden yourself with words .. But when it is brought home to you; when you see the thing you have done: when it is blinding your eyes, stifling your nostrils, tearing your heart, then –then –O God, take away this sight from me!’ (footnote omitted.) There were, of course, other figures in Shaw’s play who knew exactly what they were doing, and yet decided to do it; and who did not regret it afterwards. Some people dislike seeing their fellow men burning at the stake and others do not. This point (which was neglected by many Victorian optimists) is important, for it shows that a rational analysis of the consequences of a decision does not make the decision rational; the consequences do not determine our decision; it is always we who decide. But an analysis of the concrete consequences, and their clear realization in what we call our ‘imagination’, makes the difference between a blind decision and a decision made with open eyes; and since we use our imagination very little (footnote omitted) we only too often decide blindly. This is especially so if we are intoxicated by an oracular philosophy, one of the most powerful means of maddening ourselves with words — to use Shaw’s expression.

From Open Society and Its Enemies (Volume 2), chapter 24, section iii

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Karl Popper on the self as a unique individual

Posted on February 2, 2010 by Matt

Although I am mainly concerned with the moral aspect of the conflict between rationalism and irrationalism, I feel that I should briefly touch upon a more ‘philosophical’ aspect of the problem; but I wish to make it clear that I consider this aspect as of minor importance here. What I have in mind is the fact that the critical rationalist can turn the tables upon the irrationalist in another way as well. He may content that the irrationalist who prides himself on his respect for the more profound mysteries of the world and his understanding of them (as opposed to the scientist who just scratches its surface) in fact neither respects nor understands its mysteries, but satisfies himself with cheap rationalizations. For what is a myth if not an attempt to rationalize the irrational? And who shows greater reverence for mystery, the scientist who devotes himself to discovering it step by step, always ready to submit to facts, and always aware that even his boldest achievement will never be more than a stepping-stone for those who come after him, or the mystic who is free to maintain anything because he need not fear any test? But in spite of this dubious freedom, the mystics endlessly repeat the same thing. (It is always the myth of the lost tribal paradise, the hysterical refusal to carry the cross of civilization (29)) All mystics, as F. Kafka, the mystical poet, wrote (30) in despair, ‘set out to say . . that the incomprehensible is incomprehensible, and that we knew before’. And the irrationalist not only tries to rationalize what cannot be rationalized, but he also gets hold the wrong end of the stick altogether. For it is the particular, the unique and concrete individual, which cannot be approached by rational methods, and not the abstract universal. Science can describe general types of landscape, for example, or of man, but it can never exhaust one single individual landscape, or one single individual man. The universal, the typical, is not only the domain of reason, but it is also largely the product of reason, in so far as it is the product of scientific abstraction. But the unique individual and his unique actions and experiences and relations to other individuals can never be fully rationalized (31). And it appears to be just this irrational realm of unique individuality which makes human relations important. Most people would feel, for example, that what makes their lives worth living would largely be destroyed if they themselves, and their lives, were in no sense unique but in all and every respect typical of a class of people, so that they repeated exactly all the actions and experiences of all other men who belong to this class. It is the uniqueness of our experiences which, in this sense, makes our lives worth living, the unique experience of a landscape, of a sunset, of the expression of a human face. But since the day of Plato, it has been a characteristic of all mysticism that it transfers this feeling of the irrationality of the unique individual, and of our unique relations to individuals to a different field, namely, to the field of abstract universals, a field which properly belongs to the province of science. That it is this feeling which the mystic tries to transfer can hardly be doubted. It is well known that the terminology of mysticism, the mystical union, the mystical intuition of beauty, the mystical love, have in all times been borrowed from the realm of relations between individual men, and especially from the experience of sexual love. Nor can it be doubted that this feeling is transferred by mysticism to the abstract universals, to the essences, to the Forms or Ideas. It is again the lost unity of the tribe, the wish to return into the shelter of a patriarchal home and to make its limits the limits of our world which stand behind this mystical attitude. ‘The feeling of world as a limited whole is the mystical feeling’, says (32) Wittgenstein. But this holistic and universalistic irrationalism is misplaced. The ‘world’ and the ‘whole’ and ‘nature’, all these are abstractions and products of our reason. (This makes the difference between the mystical philosopher and the artist who does not rationalize, who does not use abstractions, but who creates, in his imagination, concrete individuals and unique experiences.) To sum up, mysticism attempts to rationalize the irrational, and at the same time it seeks the mystery in the wrong place; and it does so because it dreams of the collective (33), and the union of the elect, since it dares not face the hard and practical task which those must face who realize that every individual is an end in himself.

From Open Society and Its Enemies (Volume 2), chapter 24, section iv

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Karl Popper on Kant and a priori ideas

Posted on February 2, 2010 by Matt

The problem ‘Which comes first, the hypothesis (H) or the observation (O),’ is soluble; as in the problem, ‘Which comes first, the hen (H) or the egg (O)’. The reply to the latter is, ‘An earlier kind of egg’; to the former, ‘An earlier kind of hypothesis’. It is quite true that any particular hypothesis we choose will have been preceded by observations — the observations, for example, which it is designed to explain. But these observations, in their turn, presupposed the adoption of a frame of reference: a frame of expectations: a frame of theories. If they were significant, if they created a need for explanation and thus gave rise to the invention of a hypothesis, it was because they could not be explained within the old theoretical framework, the old horizon of expectations. There is no danger here of an infinite regress. Going back to more and more primitive theories and myths we shall in the end find unconscious, inborn expectations.

The theory of inborn ideas is absurd, I think; but every organism has inborn reactions or responses; and among them, responses adapted to impending events. These responses we may describe as ‘expectations’ without implying that these ‘expectations’ are conscious. The new-born baby ‘expects’, in this sense, to be fed (and, one could even argue, to be protected and loved). In view of the close relation between expectation and knowledge we may even speak in quite a reasonable sense of (‘inborn knowledge’. This ‘knowledge’ is not, however, valid a priori; an inborn expectation, no matter how strong and specific, may be mistaken. The newborn child may be abandoned, and starve.)

Thus we are born with expectations; with ‘knowledge’ which, although not valid a priori, is psychologically or genetically a priori, i.e. prior to all observational experience. One of the most important of these expectations is the expectation of finding a regularity. It is connected with an inborn propensity to look out for regularities, or with a need to find regularities, as we may see from the pleasure of the child who satisfied this need.

This ‘instinctive’ expectation of finding regularities, which is psychologically a priori, corresponds very closely to the ‘law of causality’ which Kant believed to be part of our mental outfit and to be a priori valid. One might thus be inclined to say that Kant failed to distinguish between psychologically a priori ways of thinking or responding and a priori valid beliefs. But I do not think that his mistake was quite as crude as that. For the expectation of finding regularities is not only psychologically a prior, but also logically a priori: it is logically prior to all observation experience, for it is prior to any recognition of similarities, as we have seen; and all observation involves the recognition of similarities (or dissimilarities). But in spite of being logically a priori in this sense the expectation is not valid a priori. For it may fail: we can easily construct an environment (it would be a lethal one) which, compared with our ordinary environment, is so chaotic that we completely fail to find regularities . . . .

Thus Kant’s reply to Hume came near to being right; for the distinction between an a priori valid expectation and one which is both genetically and logically prior to observation, but not a priori valid, is really somewhat subtle. But Kant proved too much. In trying to show how knowledge is possible, he proposed a theory which had the unavoidable consequence that our quest for knowledge must necessarily succeed, which is clearly mistaken. When Kant said "Our intellect does not draw its laws from nature but imposes its laws upon nature", he was right. But in thinking that these laws are necessarily true, or that we necessarily succeed in imposing them upon nature, he was wrong. Nature very often resists quite successfully, forcing us to discard our laws as refuted; but if we live we may try again.

Kant believed that Newton’s dynamics was a priori valid (See his Metaphysical Foundations of Natural Science, published between the first and the second editions of the Critique of Pure Reason.) But if, as he thought, we can explain the validity of Newton’s theory by the fact that our intellect imposes its laws upon nature, it follows, I think, that our intellect must succeed in this; which makes it hard to understand why a priori knowledge such as Newton’s should be so hard to come by.

From, Conjectures and Refutations, pages 47-48

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Karl Popper on the empirical base of science

Posted on February 2, 2010 by Matt

This part of my lecture might be described as an attack on empiricism, as formulated for example in the following classical statement of Hume’s: ‘If I ask you why you believe any particular matter of fact . . ., you must tell me some reason; and this reason will be some other fact, connected with it. But as you cannot proceed after this manner, in infinitum, you must at last terminate in some fact, which is present to your memory or senses; or must allow that your belief is entirely without foundation.’ [references omitted]

The problem of the validity of empiricism may be roughly put as follows; is observation the ultimate source of our knowledge of nature? And if not, what are the sources of our knowledge? . . .

The problem of the source of our knowledge has recently been restated as follows. If we make an assertion, we must justify it; but this means that we must be able to answer the following questions.

‘How do you know? What are the sources of your assertion?’ This, the empiricist holds, amounts in its turn to the question, ‘What observations (or memories of observations) underlie your assertion?’

I find this string of questions quite unsatisfactory.

First of all, most of our assertions are not based upon observations, but upon all kinds of other sources. ‘I read it in The Times‘ or perhaps ‘I read it in the Encyclopedia Britannica‘ is a more likely and a more definite answer to the question ‘How do you know?’ than ‘I have observed it’ or ‘I know it from an observation I made last year’.

‘But’, the empiricist will reply, ‘how do you think that The Times or the Encyclopedia Britannica got their information? Surely, if you only carry on your inquiry long enough, you will end up with reports of the observations of eyewitnesses (sometimes called "protocol sentences" or – by yourself – "basic statements"). Admittedly’, the empiricist will continue, ‘books are largely made from other books. Admittedly, a historian, for example, will work from documents. But ultimately, in the last analysis, these other books, or these documents, must have been based upon observations. Otherwise they would have to be described as poetry, or inventions, or lies, but not as testimony. It is in this sense that we empiricists assert that observation must be the ultimate source of our knowledge.’

Here we have the empiricist’s case, as it is still put by some of my positivists friends.

I shall try to show that this case is as little valid as Bacon’s; that the answer to the question of the sources of knowledge goes against the empiricist; and finally, that this whole question of ultimate sources – sources to which one may appeal, as one might to a higher court or a higher authority – must be rejected as based upon a mistake.

First I want to show that if you actually went on questioning The Times and its correspondents about the sources of their knowledge, you would in fact never arrive at all those observation by eyewitnesses in the existence of which the empiricists believes. You would find, rather, that with every single step you take, the need for further steps increases in snowball-like fashion.

Take as an example the sort of assertion for which reasonable people might simply accept as sufficient the answer ‘I read it in Time Times’; let us say that the assertion ‘The Prime Minister has decided to return to London several days ahead of schedule’. Now assume for a moment that somebody doubts this assertion, or feels the need to investigate its truth. What shall he do? If he has a friend in the Prime Minister’s office, the simple and most direct way would be to ring him up: and if this friend corroborates the message, then that is that.

In other words, the investigator will, if possible, try to check, or to examine, the asserted fact itself, rather than trace the source of the information. But according to the empiricist theory, the assertion ‘I have read it in The Times’ is merely a first step in a justification procedure consisting in tracing the ultimate source. What is the next step?

There are at least two next steps. One would be to reflect that ‘I have read it in The Times’ is also an assertion, and that we might ask ‘What is the source of your knowledge that you read it in The Times and not, say, in a paper looking very similar to The Times?’ The other is to ask The Times for the sources of its knowledge. The answer to the first question may be ‘But we have only The Times on order and we always get it in the morning’, which gives rise to a host of further questions about sources which we shall not pursue. The second question may elicit from the editor of The Times the answer: ‘We had a telephone call from the Prime Minister’s office.’ Now according to the empiricist procedure, we should at this stage ask next: ‘Who is the gentleman who received the telephone call?’ and then get his observation report; but we should also have to ask that gentleman: ‘What is the source of your knowledge that the voice you heard came from an official in the Prime Minister’s office?’, and so on.

There is a simple reason why this tedious sequence of questions never comes to a satisfactory conclusion. It is this. Every witness must always make ample use, in his report, of his knowledge of persons, places, things, linguistic usages, social conventions, and so on. He cannot rely merely upon his eyes or ears, especially if his report is to be of use in justifying any assertion worth justifying. But this fact must of course always raise new questions as to the sources of those elements of his knowledge which are not immediately observational.

This is why the programme of tracing back all knowledge to its ultimate source in observation is logically impossible to carry through: it leads to an infinite regress. (The doctrine that truth is manifest cuts off the regress. This is interesting because it may help to explain the attractiveness of that doctrine.)

I wish to mention, in parentheses, that this argument is closely related to another – that all observation involves interpretation in the light of our theoretical knowledge, or that pure observational knowledge, unadulterated by theory, would, if at all possible, be utterly barren and futile. [References omitted]

The most striking thing about the observationalist programme of asking for sources – apart from its tediousness – is its stark violation of common sense. For if we are doubtful about an assertion, then the normal procedure is to test it, rather than to ask for its sources; and if we find independent corroboration, then we shall often accept the assertion without bothering at all about sources

Of course there are cases in which the situation is different. Testing an historical assertion always means going back to sources; but not, as a rule, to the reports of eyewitnesses.

Clearly, no historian will accept the evidence of documents uncritically. There are problems of genuineness, there are problems of bias, and there are also such problems as the reconstruction of earlier sources. There are, of course, also problems such as: was the writer present when these events happened? But this is not one of the characteristic problems of the historian. He may worry about the reliability of a report, but he will rarely worry about whether or not the writer of a document was an eyewitness of the event in question, even assuming that this event was of the nature of an observable event. A letter saying ‘I changed my mind yesterday on this question’ may be most valuable historical evidence, even though changes of mind are unobservable (and even though we may conjecture, in view of other evidence, that the writer was lying).

As to eyewitnesses, they are important almost exclusively in a court of law where they can be cross-examined. As most lawyers know, eyewitnesses often err. This has been experimentally investigated, with the most striking results. Witnesses most anxious to describe an event as it happened are liable to make scores of mistakes, especially if some exciting things happen in a hurry; and if an event suggests some tempting interpretation, then this interpretation, more often than not, is allowed to distort what has actually been seen.

Hume’s view of historical knowledge was different: ‘… we believe’, he writes in the Treatise [references omitted], ‘that CAESAR was kill’d in the senate-house on the ides of March . . . because this fact is establish’d on the unanimous testimony of historians, who agree to assign this precise time and place to that event. Here are certain characters and letters present either to our memory or senses; which characters we likewise remember to have been us’d as the signs of certain ideas; and these ideas were either in the minds of such as were immediately present at that action, and receiv’d the ideas directly from its existence; or they were deriv’d from the testimony of others, and that again from another testimony . . . ’till we arrive at those who were eye-witnesses and spectators of the event.’ [references omitted]

It seems to me that this view must lead to the infinite regress described above. For the problem is, of course, whether ‘the unanimous testimony of historians’ is to be accepted, or whether it is, perhaps, to be rejected as the result of their reliance on a common yet spurious source. The appeal to ‘letters present either to our memory or senses’ cannot have any bearing on this or on any other relevant problem of historiography.

From "From Sources of Knowledge and Ignorance", Conjectures and Refutations, section xiii

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