Ancient Philosophy: A Very Short Introduction

Chapter 4 Reason, knowledge and scepticism

In Chapters 1 and 2 we saw how immediately gripping a topic in ancient philosophy can be, but also how we engage with the tradition in ways which reflect our own historical openness to some aspects rather than others. In Chapter 3 we explored an aspect of ancient philosophy – the ethical framework of virtue and happiness – which has turned out particularly fruitful for modern philosophical explorations. Now we shall look at some of the strands of ancient thinking about knowledge, and the lack of it, which on the face of it show more contrast than likeness to modern thinking on the topic.

In modern epistemology, or theory of knowledge, certain assumptions are common. Among them is the view that the existence of knowledge must be justified against the sceptic, that is, the person who thinks that we can never know anything, because he holds that we can never meet the conditions for knowledge. Knowledge is taken to be, at least in part, a matter of being in the right relation to facts or information. (What is this right relation? Here we find very different views, which can barely be indicated here. Some philosophers stress justification, others the right causal connection, and there are sophisticated variants and combinations of these positions.) It is hard to imagine a modern epistemologist being impressed by the thought that your mechanic knows how to fix cars. It is equally hard to think of her finding it important that someone who knows lots of facts in science, say, may lack understanding of them. And what modern epistemologist would greet an authoritative pronouncement that she in fact possessed knowledge by trying to refute it?

We can start to understand what is distinctive about ancient attitudes to knowledge by beginning with Socrates. His friend Chaerephon, we are told, asked the oracle of the god Apollo at Delphi whether anyone was wiser than Socrates, and Apollo replied that nobody was. On being told this, Socrates was surprised, and wondered what the oracle could possibly mean, since he was aware that he possessed no wisdom or expertise of his own. So he went round people considered experts, questioning them about their alleged expertise, but always finding either that they could produce no remotely adequate account of what they were supposed to be experts in, or that the expertise they did have was less important than they thought it. He concluded that Apollo’s meaning must be that the wisest person is the person most aware of their own ignorance.

Of all ancient philosophers, Socrates is the most recognizable. There is good reason for this; for ancient culture in general Socrates serves as the symbolic figure of the Philosopher. However, it is also remarkable, given that his life is elusive, he wrote nothing, and left a series of wildly differing philosophical legacies.

Socrates lived from about 468–399 BC. His father was a stonemason called Sophroniscus, his mother a midwife called Phainarete. His circumstances were initially prosperous, but by the end of his life he was poor, as a result of neglecting his practical affairs in his devotion to philosophy. His wife, Xanthippe, has an aristocratic name; she passed into legend as the shrewish wife of the undomestic philosopher, but we do not know what lies behind this. They had three sons, one young at the time of Socrates’ death. Later, unreliable tradition ascribes to him a second wife, Myrto.

In 399 Socrates was tried and executed. The charges are strikingly vague and prejudicial, and it has always been suspected that the real agenda was political. We shall never know the facts. Clearly Socrates was widely regarded as an annoying and subversive presence in Athens.

Socrates identified the practice of philosophy with personal discussion and questioning, refusing to write anything. His followers elevated him to the founding figure of their mutually conflicting approaches to philosophy. Through his austere disciple Antisthenes, Socrates was regarded as the inspiration for the convention-rejecting Cynics; through his disciple Aristippus, he was claimed as the first hedonist. Through the tradition of Plato’s Academy he was hailed as the first sceptic; through the Stoics he was regarded as the first ethical philosopher. In the writings of his younger follower Xenophon he appears as a conventional moralizer. In the writings of Plato, Socrates appears in a variety of guises. Sometimes he is the questioner who undermines the pretensions of others to understanding; sometimes he puts forward positive claims about ethics and metaphysics; sometimes he merely introduces other philosophers who have things of their own to say. Socrates continued to be influential as the figure of the philosopher par excellence, and his refusal to commit himself to authoritative teaching made him a usefully plastic figure whose influence could be claimed for widely different views and approaches.

This minimal construal of what a god means by calling a human ‘wise’ is in keeping with a Greek tradition of emphasizing the gulf between human and divine capacities. It also brings out some assumptions about ancient epistemology. Socrates goes round denying that he has knowledge, but this is never understood to mean that he does not know ordinary, everyday facts; he is aware of knowing large numbers of these. Further, he sometimes claims to know quite substantial pieces of moral knowledge, such as that he should never do wrong, or abandon what he regards as his divine mission. What he denies having is knowledge in the sense of wisdom or understanding, which goes beyond mere knowledge of isolated facts and is assumed to be found, if at all, in people who are experts in something. When Apollo says that he is the wisest person, then, Socrates is troubled by it, since if a person is an expert in something, he would normally be expected at least to be aware of what he is an expert in. He responds to the oracle by trying to find someone wiser than he is, then, not out of a rude desire to show Apollo wrong, but because he does not understand the oracle, and the only way to find out how he is the wisest person is to find out what the expertise is which he is supposed to have. And, since this is obviously not self-declaring, the only way to find it out is to see how well he compares with other people in understanding what they are supposed to be wise about or experts in; and this can only be achieved by questioning them about what they are supposed to understand.

The trial of Socrates

‘The following sworn indictment has been brought by Meletus, son of Meletus, of Pitthos, against Socrates, son of Sophroniscus, of Alopeke. Socrates does wrong in not recognizing the gods which the city recognizes, and in introducing other, new divinities. Further, he is a wrongdoer in corrupting the young.’

This indictment against Socrates was preserved in the archives of Athens and reported by later scholars. Socrates was found guilty by about 280 votes to 220. (Juries consisted of 501 citizens.) The prosecutor proposed death as a penalty. Socrates at first refused to allow that he had done anything deserving of a penalty, but eventually suggested a fine. The jury voted for death by a larger margin, about 360 to 140.

A number of points emerge in Socrates’ response to the oracle. Philosophically interesting questions about knowledge are taken not to concern our relation to particular facts – how I can know, for example, that the cat is on the mat. Philosophical attention is focused on a more complex matter: the possession of wisdom (sophia – the wisdom loved by the philosophos). It is assumed, taken to be a matter beyond argument, that wisdom is not just knowing individual facts, but being able to relate them to one another in a unified and structured way, one that involves understanding of a field or area of knowledge. (A useful parallel is that of knowing a language, which obviously involves more than knowing individual pieces of information about vocabulary and syntax, and requires the understanding of how these fit together in a unified way. The language example also brings out the way that this unified understanding is not a theoretical grasp cut off from practice, but may itself involve a practical ability to apply the understanding in question.) The philosophically interesting kind of knowledge involves a complex of items grasped together in a way that enables the knower to relate them to one another and to the structure as a whole. In all but the simplest cases this grasp will require an articulate ability to do this relating, one which will explain why the different items play the roles they do in the system. (Think of teaching a language.) Such a grasp will typically be found in someone who has expertise (techne) in a subject.

Socrates never raises the question whether there is such a thing as wisdom or expertise. This would be silly, since there obviously are experts in some fields, such as crafts. Presumably, though, Apollo meant more than that Socrates had the kind of expertise to be found in weavers and potters, so Socrates’ search is for expertise in matters of importance in human life. Hence he is particularly keen to question self-styled experts in virtue, or what is worthwhile in life, such as the sophists claimed to be. He questions them on the topics that they claim to be experts in, and always succeeds in showing that they lack understanding of these topics, since they fail to explain satisfactorily why they say what they do, and indeed often make inconsistent claims. Socrates’ questions do not start from a position of his own, since this would only weaken the point that it is the other person who is supposed to display understanding of what he claims to know. When Socrates deflates the self-styled experts by showing them, just from premisses that they accept, that they don’t understand the subject they have been pontificating about, they cannot defend themselves by faulting his views, since these have not come into it.

Differing views of Socrates

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What would show that a person has wisdom and understanding comes to be referred to as ‘giving an account’, logon didonai. Logos is the ordinary Greek word for reason; what you say about the topic you are supposed to understand must give reasons in a way that explains the matter. Socrates’ victims can produce plenty of words, but they fail to give a reasoned account of their subjects, and so are shown not to understand what they are talking about.

What are the standards for ‘giving an account’? This is obviously crucial for the question of whether you really know, that is, understand something. Minimally, of course, you have to be able to keep your end up in an argument and show that your position is consistent. But something more positive than this seems required too. One major strand of ancient epistemology consists of exploring the requirements for ‘giving an account’, providing the reasoned basis necessary if you are to have understanding of a field of knowledge.

In many of Plato’s dialogues Socrates suggests that you have to be able to provide a satisfactory answer to the questioner who wants to know what virtue is, or courage, or friendship, or the like. This is obviously not provided by trivially appealing to the meaning of words; it has to express the nature of virtue, or courage, in such a way that the person to whom it is successfully conveyed will be able not only to recognize examples of virtue, or courage, but to explain why they are examples of the virtue in question, relating them to its nature. This exploration is sometimes called a search for ‘Socratic definitions’, although ‘definition’ is an unhappy term here.

One standing puzzle about these dialogues is the following. Socrates is ambitiously searching for understanding of difficult concepts like virtue and courage. But his approach is always to question others, starting only from shared premisses. This kind of ad hominem arguing relies only on what the opponent accepts and what it produces, time after time, are conclusions as to what virtue, courage, friendship and so on are not. Some self-styled expert makes a claim as to what virtue, etc. are, and Socrates shows that this cannot be the right answer. This does not, however, seem to move us towards understanding what virtue, courage and so on are. Socrates shows that others lack understanding, but not in a way that seems to be cumulative towards obtaining understanding of his own. There appears to be a mismatch between the goal and the methods. There are many ways of resolving this puzzle, and philosophers are divided over it.

Plato has a variety of concerns with knowledge, to some of which we shall return. Some of his most famous passages, however, show the dominance of what we can call the expertise model for knowledge. What is taken to matter for knowledge is whether you can, as an expert can, grasp the relevant items in a way that relates them to one another and to the field as a whole, and can give a reasoned account of this, one which explains the particular judgements you make and relates them to your unified grasp of the whole. And in some places Plato rethinks the crucial idea of giving a reasoned account, taking mathematics as his model.

In the Republic, Plato develops possibly the most ambitious model for knowledge that any philosopher has put forward. Now the aspiring knower has to complete an apprenticeship of many years’ mathematical studies. Mathematics – by which he is primarily thinking of the kind of systematized geometry of which we have a later example in Euclid – is remarkable for its rigour, system and clarity. It struck Plato as a perfect example of the kind of structured body of knowledge that had been presupposed all along by the expertise model. Moreover, all the features of the expertise model seem to fit mathematics in a clear and impressive way. Mathematics is not a heap of isolated results; particular theorems can clearly be seen to depend on other results which are proved in turn. The whole system begins from a clear and limited set of concepts and postulates. The way in which we get from these first principles to particular results is also lucid and rigorous. It is easy to see why Plato might see in an earlier version of Euclid a splendid model of knowledge as a structured and unified system, one where it is absolutely clear what the knower knows and how she knows it, how the system holds together and what it is to give a reasoned account of what you know – namely, a proof.

Mathematics as a model for knowledge also introduces two new notes. One is that mathematical results are peculiarly unassailable; we do not waste time arguing that Pythagoras’ theorem is wrong. We have seen that certainty and justification of what is known are not prominent in the cluster of issues that are the focus of the expertise model, where what matters is understanding that can be applied in practice. But Plato is clearly at some points attracted by the idea of a body of knowledge that is not open to serious questioning.

The other point flows from the fact that mathematics provides us with a body of firm knowledge which does not seem in any plausible way to have as its object the world that we experience, in an everyday way, through the senses. Pythagoras’ theorem was not discovered by measuring actual drawn triangles and their angles, and irregularities in these are obviously irrelevant to it. Plato is attracted to the view that a body of knowledge can exist to which our access is solely by using our minds and reasoning. He is not the last philosopher to be tempted by the view that the powers of philosophical reason are more developed versions of our ability to reason mathematically.

In the Republic’s central books, we find that to have knowledge requires mastery of a systematic field whose contents are structured as rigorously as the axioms and theorems in Euclid, and linked by chains of proof. Moreover, Plato goes one better than the mathematicians in claiming that philosophy actually proves its own first principles – something which mathematicians fail to do – and so does not begin from assumptions, but shows how everything flows from a first principle which is proved and not assumed. (Here matters get obscure, particularly since Plato makes everything depend on what he calls the Form of the Good.) As with mathematics, what is known is a formal system – what Plato famously regards as the world of Forms – and not the world of experience revealed to us by the senses; indeed, Plato goes out of his way to stress the extent to which the person thinking in abstract mathematical terms will come to conclusions at odds with experience.

This is, of course, an ideal, something emphasized by the way that the only people who, Plato thinks, have a chance of attaining it are those who are exceptionally talented by nature and have been brought up in ideal cultural circumstances. This warns us against thinking that we can find any actual example of knowledge. The expertise model on its own seemed to hold out the chance at least that knowledge was attainable. But when the requirements are made as formal and demanding as they become when mathematics is the model, the conditions for knowledge get set so high as to be unattainable by us.

Aristotle, in this as in many matters Plato’s greatest pupil, takes over the Republic model, but with important modifications which make it philosophically far more fruitful. He develops the idea in his work on the structure of a completed body of knowledge, the unfortunately titled Posterior Analytics. (It is so called because it follows his treatise on logic, the Prior Analytics.)

For Aristotle, Plato goes wrong in thinking that all knowledge hangs together in a unified structure. This makes the mistake of thinking that all the objects of knowledge together make up a single system, and can be known as such. But, Aristotle thinks, there is no such single system; different branches of knowledge employ fundamentally different methods, and do so because their subject-matters are fundamentally different. Aristotle does not disagree that something like Euclid’s geometry is a reasonable model for knowledge; like Plato, he is willing to appeal to mathematics to beef up the idea of expertise. But there is no such thing as knowledge as a whole, only the different kinds or branches of knowledge – or, as we are tempted to say, sciences. (The Greek word for knowledge, episteme, forms a plural, but we cannot say ‘knowledges’, and have to make do either with ‘branches of knowledge’ or ‘sciences’. This can obscure the way that, for example, Aristotle’s notion of a science is a restriction of Plato’s conception of knowledge.)

As well as this radical ‘departmentalizing’ of knowledge, Aristotle imports a further difference. Whereas Plato focuses relentlessly on the individual knower, Aristotle widens his epistemological view to take in many aspects of the social production of knowledge. It is not for nothing that ‘science’ is more appropriate to Aristotle’s discussions of knowledge than to Plato’s. Aristotle is aware of the way that the development of a science, such as biology, requires research and observation from many people, and also that the single investigator does not reinvent the wheel every time, but relies on others’ results and data and, more importantly, on their questions and setting of the problems. He himself begins his enquiries in a number of fields by first canvassing views on it that are reputable and widely held, or put forward by philosophers or other investigators. It is by entering into this tradition of previous enquiry and exploring the problems that it has thrown up that the investigator can make progress.

Hence Aristotle can distinguish (though it would have been nice if he had done so more clearly) between different aspects of the development of a body of knowledge. The data and observations a science relies on, built up by the co-operative activities of many people, are material for a science, not science itself. Pieces of information do not constitute knowledge until they are fitted into and form part of a structured system. Hence before they amount to knowledge, the results of research and observation must be given a place within the appropriate structure. In the Posterior Analytics this structure is laid out very rigidly, and the influence of the mathematical model is very obvious. The first principles of a science must be true, primary and immediate, hold necessarily and be explanatory of the results that they are the first principles of. Much effort has gone into exploring ways in which a science like, say, biology could fit such a model, and it is generally agreed that the model is unsuitably rigid for many Aristotelian sciences. The overall point is not lost, however: empirical research is needed to gather any information worth knowing, but knowledge comes only when we see how it fits into a formal explanatory structure.

Both Plato and Aristotle have an extremely ideal model of understanding. Neither doubt that knowledge is possible in principle, though for Plato particularly the conditions become very idealized and removed from everyday life. Of course, given that they are working with the expertise model, the idea that knowledge is possible is not very radical. But what they are claiming is that we can have knowledge not merely of humdrum matters but of philosophically challenging and worthwhile subjects. Some version of this claim is common in most ancient philosophical schools.

This is not the only approach to knowledge, however; we find very different ones. The most radical of these is traced in part to Socrates and in part to Pyrrho, a later philosopher who also wrote nothing. This is ancient scepticism (making Socrates one founder of scepticism). Unlike modern scepticism, the ancient movement does not limit itself to denying that knowledge is possible, leaving us with true belief. Ancient scepticism is as concerned with holding beliefs as with knowledge, and is best thought of as an intellectual position concerning the powers of reason, one far more radical than modern scepticisms.

The sceptic begins like everyone else, by searching for truth and for knowledge. This he does by investigating, querying others’ reasons for what they claim, and looking for supporting reasons for positions of his own. So far there is no disagreement with the basic idea that knowledge requires the giving of a reasoned account. Knowledge of any kind worth having (that is, not knowledge of everyday bits of information) requires that you be able to give satisfactory reasons for what you claim. What distinguishes the sceptic from other philosophers is just that he never regards himself as having got to that point. The Greek term skeptikos means, not a negative doubter, but an investigator, someone going in for skeptesthai or enquiry. As the late sceptic author Sextus Empiricus puts it, there are dogmatic philosophers, who think that they have found the truth; negative dogmatists, who feel entitled to the position that the truth cannot be found; and the sceptics, who are unlike both the other groups in that they are not committed either way. They are still investigating things.

Pyrrho of Elis (c.360 – c.270 BC) is, like Socrates, an influential philosopher who inspired others but wrote nothing himself. His life is even more elusive than that of Socrates, and unlike him he left no visual image.

Originally a painter, Pyrrho at some point was influenced by various philosophical schools. He accompanied Alexander the Great on his conquest of northern India, where he encountered Indian ‘gymnoso-phists’ or naked wise men. It has been claimed that this encounter was decisive for his own philosophical stance, and similarities have been claimed between reports of his arguments and early northern Indian Buddhist texts. The Greeks, however, found no problem in interpreting Pyrrhonism in Greek terms, especially as Pyrrhonists always argue against the views of others, and so developed a repertory of attacks on existing philosophical theories.

Pyrrho himself impressed others by the example of tranquillity and impeturbability he gave in refusing to commit himself to any dogmatic belief. Stories about him abound, but are mostly hostile jokes to the effect that he suspended judgement in everyday matters, thereby making himself ridiculous. Other stories say that he lived a respectable life and that Elis exempted philosophers from taxation in his honour. His pupil Timon wrote satires against dogmatic philosophers, and also prose accounts of Pyrrho’s arguments which, though problematic, show them as forerunners to the later versions of these arguments, especially those found in our main sceptical text, Sextus Empiricus’ Outlines of Pyrrhonism (of uncertain date but probably second century AD).

Why the problem? Surely if you investigate you will turn up some results that can count as knowledge or at least as belief. Sceptics think that, while we want to think this, it will always turn out to be rash (or ‘precipitate’) assent: we committed ourselves too soon. Real inquiry, thorough investigation, will reveal that the situation was more complex and problematic; we turn out never to have reason to commit ourselves one way or the other, and so end up suspending judgement – that is, having a detached and uncommitted attitude to whatever the issue was.

At first this sounds ridiculous, indeed unserious. Does the sceptic really hold that we can never establish what time it is, that the sun is shining, that this is bread and not grass? This is an ancient reaction, but a mistaken one.

Pyrrho, the founding figure of one branch of scepticism, is someone about whom we know little, and our accounts of his intellectual attitudes are frustratingly meagre. His uncompromising attitude about our never having reason to commit ourselves to anything led to unfriendly jokes, such as that he had to be looked after by unsceptical friends to stop him walking off cliffs, and the like. But there is an alternative tradition to the effect that he lived a normal life, so it is most probable that, like later sceptics, he took it that even when we cannot commit ourselves to beliefs we can live by the way things appear to us.

Later sceptics who took their inspiration from Pyrrho developed the idea that we ‘live by appearances’. That is, all we need to live is for things to appear to us in one way rather than another. If we go beyond this (which we get inclined to do when we move on from everyday matters to issues where there is dispute and complexity) and try to commit ourselves to beliefs, we will always in fact find, if we investigate rigorously, that we cannot commit ourselves; there turns out to be equally good reason on both sides of the question, so that we find ourselves equally inclined both ways, and so end up uncommitted, suspending judgement on the issue. This does not leave us paralyzed, however, since we still have the appearances to live by. The fact that I cannot commit myself does not stop things appearing to me one way rather than another. Being rationally uncommitted does not do away with all the other sources of motivation that get us by – habit, desire, fear of the law and so on. The view that if reason does not commit us we cannot go on living comes from an over-estimation of the powers of reason, which we do not always need and which tempts the dogmatist into committing herself prematurely to the truth of some theory.

Moreover, the sceptics go on the offensive here. What we want out of rational commitment to our beliefs, they hold, is happiness, which is to be found in peace of mind; we want to feel confident about the way things are and not worried by our uncertainty about them. But commitment to positive or negative theories on the topic can never do this; all it can do is displace or redirect the original anxiety. Only the sceptic, who realizes the futility of commitment to belief, is tranquil; rigorous investigation brings suspension of belief, and this brings the peace of mind that had been sought in the wished-for answers. Hence only the sceptic gets what everyone else is looking for, peace of mind. But she gets it only by not looking for it, merely being there when it arrives; and it arrives as a result of the rigorous investigation that makes it impossible to commit yourself for or against any position.

There is much in the sceptical story that is implausible, or seems forced. Moreover, problems lurk which can be barely mentioned here. What is the scope of the sceptic’s suspension of belief? Does it extend only to matters on which she investigates? If so, does she have some beliefs, namely the unproblematic ones? Anyway, what is the sceptic doing telling us all this about how to achieve peace of mind, how others fail, and the sceptic succeeds? How can she do this without holding beliefs?

Ancient scepticism is one of the most interesting and subtle philosophical positions. Like its dogmatic cousins, it embodies strong assumptions about reason, though subversive rather than positive ones, and is both deeper and broader than modern forms of scepticism which limit themselves to complaints about knowledge, and may reject some subject-matters on the basis of uncritically accepting others. Ancient sceptics, unlike moderns, are uninterested in carving out a position within philosophy; they think that philosophical reason, when exercised, will always undermine itself.

Socrates provided an alternative inspiration for the other branch of ancient scepticism, which took over Plato’s Academy from the middle of the third century BC until its end in the first century BC. The Academics held that philosophizing in the spirit of Plato should take the form of doing what Socrates did, namely undermining the claims of others while putting forward none of your own. Hence the sceptical Academics spent their time arguing ad hominem (that is, not from any position of their own but only from premisses the opponent accepts) against dogmatic philosophers whose claims they thought inadequately grounded, mostly the Stoics. Unlike the Pyrrhonists, the Academics made no claims about happiness or peace of mind. Their assumption about reason is simply that dogmatic philosophers have always been too hasty; their claims can be overturned from within and not by relying on the establishment of other positions.

So far we have seen bold and radical positions, both positive and negative, about knowledge and belief. It would be misleading, however, to give the impression that ancient concerns with knowledge always focus on wisdom and understanding; we can also find concerns which overlap with modern ones. Plato, for example, produces interesting arguments against relativist theories of knowledge which do not rely on any of the special features of his own ambitious account. A relativist, such as Protagoras, against whom Plato argues in the dialogue Theaetetus, claims that for someone to have a true belief is no more than for something to appear true to him, and hence that truth is relative to the believer. This can seem at first like a liberating discovery, especially since it defuses all disagreement. The wind appears hot to me, cold to you; we are both right, and there is nothing to argue about. Protagoras, however, puts his relativist theory forward as a theory, something we should accept and take seriously (if only in order to be liberated from our disagreements). But if Protagoras is right, the truth of his own theory is relative to him – that is, it is just the way things appear to him. And why ever should we accept, or be interested in, what happens to appear a certain way to Protagoras? If we are to take relativism seriously as a theory, then relativism cannot hold of it. (Versions of this powerful point are still being made against modern forms of relativism.)

Plato is also interested in the question of what is going on when we are said to know particular facts, and this is developed by the Stoics, who retain the expertise model for what they call knowledge proper, but also develop an account of what they call apprehension, which amounts to one way of thinking of knowledge, especially in some modern epistemological theories. Apprehension is what you have when you are so related to an empirical fact that you cannot be wrong about it. The Stoics put some effort into working out what the conditions have to be for this to hold. Roughly, the thing in question has to make an impact on you, an impression; and this impression must come from the thing in the right way – the causal story must be the right one; and the impression must be one that you could not have had from any other thing, however similar. These conditions were seen as a challenge to produce counter-examples, where the conditions are all met, but we have to agree that we do not have knowledge. The Academic Sceptics in particular carried on a long debate with the Stoics on this topic, as a result of which the Stoics seem to have introduced further conditions and modifications.

Epicurus’ theory is, untypically for ancient theories, rigorously empiricist – that is, it begins from and relies on our sense-experience. What I know comes to me through the senses, since only sensations relate information to me in a way which is unmediated by a process which could involve error. My ordinary beliefs, arrived at in ways which involve inferences going beyond experience, contain truths, but also falsehoods that have crept in through the human propensity to get things wrong. But if I concentrate only on what the senses tell me, I cannot go wrong. For Epicurus, belief and reasoning are sources of error, not, as for most other schools, the source of our ability to correct error. Error, then, comes in only when I start adding beliefs to what the senses tell me. Hence it turns out that what the senses tell me is not even as extensive as claims about tables and towers – since obviously these can be mistaken, as when we judge from a distance that a square tower is round. Rather, the reports of the senses are limited to how the tower appears to us from a particular perspective at a particular place, and so on. Hence we have knowledge, since we cannot be wrong about this. We could, however, be wrong about the tower, since we might make a claim that did not make due allowance for perspective, distance etc. Our knowledge turns out to be far more limited than our everyday observations about the world around us.

Epicurus’ theory of knowledge was not regarded as particularly impressive; indeed it was widely regarded as hideously crude. Later Epicureans, however, did develop interesting analogues of what we think of as issues of induction – how, from a number of particular observations, we can come to make justifiable generalizations about all occurrences of this kind of thing. Are we justified, for example (‘we’ being Epicurean philosophers living in Italy) in inferring that because all the humans we have observed are mortal, so are humans in hitherto undiscovered countries, such as Britain? (If there are any humans there, adds Philodemus, the philosopher whose example this is.)

Empiricist theories of knowledge, like an emphasis on the knower’s relation to particular facts, are the minority stream in ancient epistemology. What emerges from even a cursory survey of ancient concerns with knowledge, however, is the width and diversity of approaches. A student of epistemology in the ancient world would find a number of challenging theories and an extensive tradition of debate. She would find several ways of understanding knowledge: theories about wisdom and theories about apprehension of particular facts, theories privileging abstract reasoning and theories privileging the basic reports of the senses. She would also find extensive engagement not just with knowledge, but more generally with problems of belief and the powers of reasoning, both positive and negative.