How do I know?

Philosophy is alive and well – at least in Australia. Don’t listen to the windy voices who tell the public that metaphysics is dead, its foundational role exposed as an illusion, and that epistemology should never have begun. All it takes to show the futility of such talk is the example of someone who has found a genuine philosophical issue and who is able to discuss it with verve, ingenuity, insight, and a good sense of how the philosophical argument relates to controversial questions in neighbouring fields of inquiry.

C.A.J. Coady is a professor of philosophy, and director of the Centre for Philosophy and Public Issues, at the University of Melbourne. The achievement of his book Testimony is to demonstrate that I know nothing on my own. All my knowledge is in part ours. The aim of this review is to explain why the book is an important event in philosophy. Coady’s work should change the way we think about the nature and scope of human knowledge.

Let us begin, as modern philosophy so often does begin, with Descartes sitting by the fire, meditating how to reach certain knowledge of the world we live in. His concern is general: how can we assure ourselves that certain knowledge is attainable? But his solution is individualistic in the extreme. He argues that he (and similarly anyone else who is serious about the question) should begin by setting aside as in principle open to doubt every opinion he has acquired, either from the senses or through the senses, where ‘through the senses’ extends the doubt to everything he has been taught or told by other people. That Julius Caesar crossed the Rubicon, for example, is not an opinion Descartes acquired by observing the event with his own senses; he got it by seeing or hearing the words of other people. The remarkable thing is that this preliminary statement about the testimony of other people – to the effect that it is always open to doubt – is also the Meditations’ last word on the subject.

Descartes does return to the question of what he can gain ‘from the senses’. At the end of the Meditations, when the method of doubt has assured him of the attainability of certain knowledge (certain precisely because it was reached by doubting everything that can be doubted), he is in a position to restore a measure of trustworthiness to the reports of his own senses. But he has nothing to add about when it is reasonable to trust the reports of other people. The guiding assumption throughout is that if I am to achieve knowledge of the world I live in, I must do it entirely by myself. And so must you. Knowledge, as opposed to opinion, is something that each of us must work at for ourselves.

Such is the extreme ‘epistemic individualism’, as Coady calls it, of the founding work of modern philosophy. But epistemic individualism was not invented by Descartes. Coady quite rightly begins much earlier, with Plato. In an influential passage of Plato’s Theaetetus, a jury passes judgment on a crime they did not witness. Suppose they get it right. Having been told about the crime by people who did see it, they decide that it was indeed Jones, not Smith, who was responsible. Do the jury know that Jones was the villain? According to Plato, they cannot possibly know this – and not just because conditions in a court of law are not ideally suited to the achievement of knowledge as opposed to true opinion. Even in ideal conditions, ‘only an eyewitness could know.’

The implications of Plato’s dictum are radical. No eyewitness who does know about an event or state of affairs can transmit their knowledge to someone else, not an eyewitness, in such a manner that the other person knows at second hand. There is simply no such thing as second-hand knowledge. At a stroke, the possibility of historical knowledge, and much else, is dismissed.

Plato is by no means the only philosopher in our tradition to hold such a view. Here is John Locke on the subject of second-hand knowledge in philosophy and the sciences:

we may as rationally hope to see with other men’s eyes as to know by other men’s understandings. So much as we ourselves consider and comprehend of truth and reason, so much we possess of real and true knowledge. The floating of other men’s opinions in our brains makes us not one jot the more knowing, though they happen to be true. What in them was science is in us but opiniatrety, whilst we give up our assent only to reverend names, and do not, as they did, employ our own reason to understand those truths which gave them reputation.

Or take Augustine, who was not, like Plato, scornful of beliefs that fall short of knowledge. Augustine wrote extensively about the importance of faith and testimony; we should accept the historical narratives of the Bible, for example, as a true account of events in the distant past that we have not witnessed for ourselves. But he also wrote the De Magistro, which argues that no human being can teach another anything in the sense of imparting knowledge to them. I never know a truth unless in some appropriate sense I have seen it for myself.

Even philosophers who do acknowledge the existence of second-hand knowledge tend to define it in terms that make it virtually impossible to attain. Since Hume the standard view, elaborated in various versions, has been that it can be right to believe what someone else tells me, and in favourable circumstances my belief may amount to knowing at second hand, only if I have independent evidence that the other person is a reliable source of information on the matter, or the kind of matter, in question. But often my evidence of their reliability will itself derive from testimony. I take John to be an honest reporter not because I have checked his stories for myself and found them to be accurate, but because other people say he is. Are they reliable? If testimony always stands in need of independent justification, I should check up on them too. Where will it end?

To show that this whole project of justifying testimony is misconceived, Coady invites the reader to perform a partial repeat of Descartes’s meditation. How much knowledge will you be left with if you discard as doubtful everything that depends on the say-so of other people whose reliability you have not yourself checked on? Put in more positive terms, how much of your present knowledge has been gained entirely, as epistemic individualism requires, by your own reason, observation and memory?

You may as well begin by doubting that an Australian philosopher called Coady has written a book on testimony. You do not even have my word for it – only the word of the London Review of Books that I am the author of this review. You can of course go to a bookshop and read the dustjacket. But have you personally checked the reliability of dustjackets, or of dustjackets from Oxford University Press? As for the existence and location of a country called Australia, many people know of it only from maps, teachers and TV fiction.

The epistemic individualist may object that, while we do normally accept on trust a vast amount of information from each other, this information should not count as knowledge, or even as reasonable belief, unless our trust rests ultimately on grounds that are independent of testimony and accessible to each individual’s powers of reason, memory and observation.

For this objection to succeed, reason, memory and observation must themselves be cleansed of testimony. For as Coady points out, much of what passes for observation is already enriched by the testimony of other people. Did you see the Australian team trounce England in the test match? Their being Australian is not an observable phenomenon like the movement of ball and bat. Unless you travelled with them in the plane from Australia, you knew it was Australians you were watching only because they and everyone else proclaimed the fact. And how, independently of the word of other people, could you have known it was a test match?

The same holds for many of the results of reason. Scientists and technicians, historians and scholars, rely constantly on other people’s reports of their discoveries, experiments, documents, manuscript readings etc. It would be insanity to repeat every experiment and check every document, and no less insane to try to verify the reliability of all those predecessors who have reported them to us. No one would get to any new conclusions, no one’s understanding would advance.

And it is not just a matter of the data from which reasoning proceeds. The very concepts which help in the advancement of understanding presuppose the validity of beliefs that derive, to a greater or less extent, from testimony; think of the expanding universe, inflation, or even so simple an idea as forgery. In this very obvious sense, science and the humanities are a communal achievement.

The argument so far may seem to prove only that for lack of time and energy we are forced to take a vast amount of information on trust from our fellow human beings. But-Coady also questions whether even in principle it is possible to justify testimony. Such a justification could succeed only if the outcome might in principle be negative, in the sense that it could turn out that we are wrong to make a practice of trusting other people. But could it?

Suppose some Martians want to find out about our life, our world, and its history. Much time and energy would be saved if all they had to do was learn our languages and then ask us, or read our books and newspapers. So they appoint an Examiner to discover how far we Earthlings are to be believed. To do this the Examiner will need, first, to work out which sentences in a given human language are meant as reports of the past or as testimony to some matter not accessible to current observation, and, second, to find ways of determining whether these sentences, or certain classes of them, are generally correct or generally incorrect. Stage one is linguistic interpretation, stage two an assessment of the interpreted sentences as true or false.

The difficulty is that if, as the inquiry proceeds, the results begin to suggest a verdict of ‘generally incorrect’, that will cast doubt on the correctness of the Examiner’s initial interpretative hypothesis as to which sentences in the language are meant as reports and testimony. There is no possible state of affairs in which the Examiner could reasonably conclude both that the linguistic interpretation is correct and that the bulk of the interpreted sentences are incorrect. Hence the Examiner could never be justified in reporting to his fellow Martians that human testimony is reliable.

But, the argument continues, the epistemic individualist is someone who aims to play the part of the Examiner. It is no more possible for the one than for the other to find out that testimony is unreliable. Hence the epistemic individualist’s goal of a testimony-independent justification of testimony is in principle, not merely in practice, unattainable.

The pattern of argument just sketched is one that has been very popular in recent philosophy. Its most notable proponent is Donald Davidson, who has inspired a good deal of discussion about how exactly the premises and conclusion of such arguments are best formulated. But so far as I know, Coady is the first person to extend the reasoning into the area of testimony. He gives due attention to the technical niceties of formulation, and much more detail than I have reported. He also has the example the other way round: we are examining the Martians. I have reversed the roles in order to smooth the transition from the Examiner to a character I shall call the Pupil. For I believe that the most important lesson of Coady’s book is to be found in the remarks he makes, in various places, about the Pupil.

The moral of the Martian tale was that it is impossible to separate interpretation and verification into two neat stages. Interpretative hypotheses about which sentences of an alien language are meant as reports must go hand in hand with certifying many of them as true; too much falsity will send the Examiner back in search of a better account of which sentences meant what. But the epistemic individualist already knows which sentences mean what. Such a person learned at least one human language, as we all do, long before they developed the elaborate cognitive abilities that the Examiner must have even to formulate, let alone to try to carry out, the task of assessing the reliability of human testimony in general. That is to say, the epistemic individualist was once, like everyone else, in the position of the Pupil.

The Pupil is a child learning a language and learning about the world for the first time. It is no more possible for the Pupil than it is for the Examiner to learn the language first and then discover what is true about the world, and it would be misleading even to speak of two learning processes going on at the same time. There is a single process in which language and the world are learned together in relation to each other. The great difference between the Examiner and the Pupil is that the Pupil has to be initiated both into the language and into the surrounding world through the guidance of other people. For the Pupil is still in the early stages of learning, along with everything else, how to learn about the world and how to assess other people’s statements as true or false. And this too requires the guidance of other people, even though the urge to learn is active from birth. So inevitably the Pupil begins by taking things on trust. Children do not trust everyone or everything they say. But the fact remains that trust is where we all begin.

In philosophy there is a role for plain fact, as well as for the imaginative exploration of possibility through Martian tales. Even Descartes acknowledged the inevitability of beginning from trust. In his Discourse on Method he wrote:

we were all children before being men and had to be governed for some time by our appetites and our teachers, which were often opposed to each other and neither of which, perhaps, always gave us the best advice; hence it is virtually impossible that our judgments should be as unclouded and firm as they would have been if we had had the full use of our reason from the moment of our birth, and if we had always been guided by it alone.

Coady treats the same fact, more positively, as just one facet of the trusting dependence that permeates the life of children. Accepting an adult’s word on the difference between bed and bunk, mauve and purple, is as natural as taking their hand to cross the road. Trusting the person is not to be separated from trusting their word on what to say and what to believe. Such multi-faceted trust is an intrinsic part of what Wittgenstein had in view when he wrote: ‘What has to be accepted, the given, is – so one could say – forms of life.’

Yet the philosophical hero of this book is not Wittgenstein (though his influence is acknowledged), but the 18th-century Scottish philosopher Thomas Reid. Reid is the one philosopher in the tradition to have explicitly attacked epistemic individualism. He denied that the practice of relying on testimony can be justified by any one individual’s reason, observation and memory. Insofar as it is useful to think of knowledge as a building with foundations, then testimony is part of the foundations.

An old saying has it that man is by nature a social animal. If we take this seriously, we ought to accept that an accurate account of the nature and scope of human knowledge must include as basic, not only the traditional powers of reason, observation and memory, but also what Reid calls ‘social operations of mind’: those operations which presuppose, as he put it, ‘intercourse with some other intelligent being’. Examples are the giving and receiving of commands, promising, asking questions – and giving and receiving testimony.

Inspired by Reid, Coady defends the claim that learning from others is as basic an operation of the human mind as observing, remembering and reasoning:

I ring up the telephone company on being unable to locate my bill and am told by an anonymous voice that it comes to $165 and is due on 15 June. No thought of determining the veracity and reliability of the witness occurs to me nor, given that the total is within tolerable limits, does the balancing of probabilities figure in my acceptance.

What Coady the telephone subscriber accepts on trust, Coady the philosopher claims should count, in the circumstances described, as direct, non-inferential knowledge. Of course, it would not be knowledge if the voice was reading from a bill of someone else with the same name. But the non-existence of a homonym is not a premise from which Coady infers (or should, if he was scrupulous, infer) that $165 is the amount to write on his cheque. He knows it, because he has been told. End of explanation. Human knowledge is built on trust.

Although Testimony is not a work of political philosophy, several striking passages of the book show that Coady is well aware of the social and political implications of his emphasis on trust. No doubt it will encounter resistance, both political and epistemological. To emphasise trust as a political value runs counter to current government programmes for commercialising relationships like those of doctor and patient, teacher and pupil, which in the past were based on trust. And there is, of course, a political dimension to many of the reasons typically given for being sceptical about the epistemological worth of testimony. In the face of propaganda, biased newspapers, lying politicians, the notorious unreliability of identification parades, the gullibility of people through the ages, who can deny the need for caution about accepting the word of other people?

To nagging doubts like these Coady replies with chapters on testimony in the law, on the findings of experimental psychology, on reports of miracles and other astonishing events, on historical methodology, and much else. Epistemic individualists need not take my word for it that Coady has his answers to the standard problems. Read the book and judge it for yourselves.

A further reason for reading the book is as a corrective to the ‘externalism’ of much recent epistemology. Externalism is the idea that the difference between knowledge and true belief is not to be explained in terms of justification or reasons accessible to the knowing subject. The difference lies entirely in the external relation of the belief to the fact that makes it true. The belief is a case of knowing if the route by which it was acquired is reliable, regardless of whether the subject is in a position to assess its reliability. The moral an externalist would draw from the story I have been telling is not that it shows what is wrong with the epistemic individualist’s insistence that testimony stands in need of justification, but that it shows what is wrong with the view that knowledge as such requires justification.

Coady refuses to bow to current fashions in this matter, and rightly. Even if externalism gives a good answer to the question ‘What is knowledge?’ for those who are in search of knowledge the first-person questions remain. Are we satisfied beyond reasonable doubt that Jones is the villain? Should we distrust the witnesses who testified that he did not do it? Can we, who were not present at the scene of the crime, know better than those who were? These questions require answering in terms of reasons accessible to the subject. Both in the juryroom and in everyday life justification has its role, a role that would remain important even if we let the externalist take charge of the concept of knowledge and recast the discussion exclusively in terms of reasonable belief. For if knowledge is not the same as justified true belief, knowledge is not the only epistemic goal. We want justified true belief also.

Justification has to come to an end somewhere. There have to be reasons for which no further reasons need be given. In the appropriate circumstances ‘I saw it with my own eyes’ can serve as such a reason. So can ‘I remember,’ or ‘It follows from what we already know.’ Coady’s claim, amply justified in this excellent book, is that the ultimate reason is often: ‘That’s what I was told.’ Without such expressions of trust human life would be solitary, poor, nasty, brutish and ignorant.