How do I know?

M.F. Burnyeat

  • Testimony: A Philosophical Study by C.A.J. Coady
    Oxford, 315 pp, £40.00, April 1993, ISBN 0 19 824786 9

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.

The full text of this book review is only available to subscribers of the London Review of Books.

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