In his essay ‘On Being Modern-Minded’ (1950), Bertrand Russell describes a particularly seductive illusion about history and intellectual progress. Because every age tends to exaggerate its uniqueness and imagine itself as a culmination of progress, continuities with previous historical periods are easily overlooked: ‘new catchwords hide from us the thoughts and feelings of our ancestors, even when they differed little from our own.’

Behavioural economics is one of the major intellectual developments of the past 50 years. The work of the psychologists Daniel Kahneman and Amos Tversky in particular is justly celebrated for identifying and analysing many of the core biases in human cognition. Russell’s insight, in fact, bears a strong resemblance to what Kahneman calls the availability bias. Because the catchwords and achievements of contemporary culture are most readily called to mind – most available – they tend to dominate our assessments. The fact that Russell’s articulation of this idea is much less familiar than Kahneman’s is itself a confirmation of Russell’s point.

But the richest precedent for behavioural economics is in the works of ancient Greek philosophers. Almost 2,500 years before the current vogue for behavioural economics, Plato was identifying and seeking to understand the predictable irrationalities of the human mind. He did not verify them with the techniques of modern experimental psychology, but many of his insights are remarkably similar to the descriptions of the cognitive biases found by Kahneman and Tversky. Seminal papers in behavioural economics are highly cited everywhere from business and medical schools to the social sciences and the corporate world. But the earlier explorations of the same phenomenon by Greek philosophy are rarely appreciated. Noticing this continuity is both an interesting point of intellectual history and a potentially useful resource: Plato not only identified various specific weaknesses in human cognition, he also offered powerful proposals for how to overcome these biases and improve our reasoning and behaviour.

Many of Plato’s dialogues dramatise the habits and processes that lead humans to false conclusions. He depicts people believing what they want or what they are predisposed to believe (confirmation bias); asserting whatever comes most readily to mind (availability bias); reversing their opinions about identical propositions based on the language in which the propositions are presented (framing); refusing to relinquish current opinions simply because these happen to be the opinions they currently possess (a cognitive version of loss aversion); making false inferences based on the size and representativeness of a sample of a broader population (representativeness heuristic); and judging new information based on salient current information (a version of anchoring). And this is only a partial inventory of the mental errors that he catalogues and dramatises.

There’s a reason why Socrates, in the Republic, compares philosophical enquiry to a hunt for an elusive quarry – discovering the truth about things is difficult, and simply trusting our first impressions and beliefs is a recipe for misapprehending the world. Only by rechecking arguments both for validity and soundness, and becoming acutely aware of our own susceptibility to certain forms of deception, are we likely to get closer to the truth. Socrates’ various interlocutors across the Platonic dialogues include the young and the old, politicians and laymen, intellectuals and slaves, doctors and mystics, the drunk and the sober, the very rich and the middle class. While the character traits of particular individuals do affect their susceptibility to different fallacies and mental errors, this broad demographic range suggests a dramatic approximation of a large and representative sample of the population. Plato sought to study general features of human psychology, not just to depict the quirks of individuals.

One of these general features is a tendency to draw premature conclusions from insufficient evidence. In a passage of the Phaedo, Socrates warns against despairing about the legitimacy of all arguments after being tricked by the clever sophistries of a few specious ones. He draws an analogy with the origins of misanthropy:

Misanthropy arises out of the too great confidence of inexperience – you trust a man and think him altogether true and sound and faithful, and then in a little while he turns out to be false and knavish; … and when this has happened several times to a man … he at last hates all men, and believes that no one has any good in him at all.

Whether this leads to a hatred of humans or of arguments – Socrates dubs the latter ‘misology’ – the cause is identical.

The blunder of the misologist is not only to rely on a small sample size; he also mistakes its representativeness. If regression to the mean and normal (Gaussian) distributions were not regular phenomena in the world, the small sample size would be less likely to pose a problem. But Plato recognises that outliers are rare, and that things in the world do tend to fall along bell curves, though he does not use this terminology:

[F]ew are the good and few the evil … [Just as] you might say of the very large and very small – that nothing is more uncommon than a very large or very small man; and this applies generally to all extremes, whether of great and small, or swift and slow, or fair and foul, or black and white: and whether the instances you select be men or dogs or anything else, few are the extremes, but many are in the mean between them.

In their celebrated paper ‘Subjective Probability’ (1972), Kahneman and Tversky found that people judged it equally likely that a group of men would have a mean height over 6 feet tall, regardless of whether the group size was 10, 100 or 1,000 men. As Plato saw, variability is likely to be higher in a small sample; if you meet only a small number of men or arguments, you might indeed come across a string of atypically tall men or bad arguments.

Plato understood that susceptibility to distorted reasoning was a matter of ethics as well as psychology

Framing is another discovery of modern psychology that has ancient philosophical origins. People – including doctors – often assess the same medical intervention differently if its impact is framed in terms of lives saved versus deaths expected. Modern researchers have found versions of the phenomena everywhere from politics to consumer preferences. Plato’s work on ‘framing’ appears in many dialogues, both as formal analysis and dramatic depiction. In the Theaetetus, he observes that the same number of dice – six – can appear greater or smaller if juxtaposed to either four or 12 dice. He gives a different example in the Republic about the relative size of human fingers: the third is large compared to the fourth (the pinky) but small compared to the middle finger. This is a basic point about arithmetic but a profound one about psychology and perception. Saying that a new soft drink has only half the calories of a Coke sounds much more attractive than saying that a new soft drink has 18 times the calories of a carrot. We easily mistake relative and absolute scales of measurements – if X is larger than Y, and only Y is presented as a comparison, it’s easy to assert that X is large in an absolute sense. We might come to think of this new soft drink not as less sugary but as not sugary.

An especially interesting instance of framing involves our assessments of relative levels of pleasure and pain. Distinguishing relative and absolute magnitudes of objects outside the body is one thing, but what happens when we are judging the quantity of a sensation – perhaps represented as a number on a pain scale – that pervades our sensory awareness at every conscious moment? After experiencing terrible pain, for instance, the absence of that pain feels wonderful, just as the sudden absence of a sublime pleasure can be wrenchingly painful. Plato cautions here against mistaking relative for absolute values: ‘Let us not, then, be induced to believe that pure pleasure is the cessation of pain, or pain of pleasure.’ He makes this observation not only to establish a point about human psychology. The ultimate purpose of the example is to support an argument about how we should live our lives. Those who base their happiness on pursuing sensual pleasures preceded by the pain of acute cravings measure the magnitude of the jolt of pleasure they get from satisfying their cravings only within the local context of the pain that precedes it. This is one of many reasons for preferring the pleasures of the mind to those of the body – intellectual pleasures are not typically preceded by intense pains.

It’s rare that contemporary discussions of cognitive biases flow directly into conversations on ethics, pleasure and pain, and the best way to live one’s life. But ancient philosophy did not compartmentalise what are now cloistered academic fields. Plato understood that susceptibility to distorted reasoning was a matter of ethics as well as psychology. This does not mean anything as simple as ‘bad people are more vulnerable to cognitive biases’. But consider his diagnosis of misanthropy and other sampling errors, which stem from ‘the too great confidence of inexperience’. In the Apology, Socrates claims to be wiser than other men only because he knows that which he does not know. When Kahneman writes that we are ‘blind to our blindness’, he is reviving the Socratic idea that wisdom consists in seeing one’s blindness: knowing what you do not know.

Intellectual humility and overconfidence can stem from purely cognitive processes, but they are also correctly understood as moral achievements or failings. Someone who always thinks that he is right about everything, however little he knows, is making a moral as well as a mental mistake. Similarly, the cultivation of intellectual humility is, in part, the cultivation of an ethical virtue. Many of the early Socratic dialogues end in uncertainty: the characters are reduced to what in ancient Greek was called aporia, and is often rendered in English as ‘perplexity’, ‘bafflement’, or ‘confusion’. Socrates’ interlocutors search for a satisfying answer to some question only to find that every proposed answer fails to satisfy tests of logical consistency. Characters react in different ways to this process – some become flustered, some threaten violence, some run away, and a few recognise that they have been improved, and express gratitude to Socrates. Their false steps in the arguments dramatise errors in reasoning, but their emotional reactions are the stuff of literature: they reveal hubris and arrogance, modesty and generosity, and the dynamic struggles between these opposed impulses – what the novelist William Faulkner in 1950 called ‘the human heart in conflict with itself’.

By dramatising the moral dimensions of cognitive biases, Plato suggests that, while susceptibility to these errors could be universal, our capacity to overcome them stems in part from the correct ethical training. Socrates might have endorsed precisely half of the poet John Keats’s lovely praise for the value of ‘being in uncertainties, mysteries, doubts without any irritable reaching after fact and reason’. This is only a preliminary step in Plato’s dialogues – a (good-natured) reaching after fact and reason should and does occur – but an initial tolerance of uncertainty is a capacity without which individuals and societies cannot adequately self-correct and improve. People who are pained and irritated by not knowing something reach prematurely for whatever apparent reasons are most accessible.

In one ancient demonstration of what Kahneman calls the availability heuristic, the character of Euthyphro defines piety as exactly what he has done immediately before beginning his conversation with Socrates. Because this is the first example that comes to mind, Euthyphro naturally offers his own behaviour as a paradigm case of piety – the concept that the dialogue investigates. Consider the difference between saying ‘I am doing X because it is right’ and ‘X is right because I am doing it’. Euthyphro unwittingly falls into the trap of the latter while believing he is doing the former. Plato suggests that a remedy for this tendency must involve changing what gives us pleasure and pain – lessening the pain associated with uncertainty or decreasing the pleasure derived from proving that one is right. These are ethical challenges as much as intellectual ones.

Intelligence is some protection against the seductions of fancy yet vapid words, but a lack of pretentiousness is also an asset

A case from Plato’s Meno offers an intriguing example that cuts across some of the modern categories of cognitive biases. Socrates is attempting to provide an adequate definition of colour. He gives his first definition in simple language, and Meno rejects it. Without improving the definition, Socrates rephrases it in grandiose terms, and Meno is instantly satisfied. Socrates explains the change in Meno’s response like this: ‘that’s probably because it’s in the manner to which you are accustomed … And so you prefer it.’ To the extent that the customary is more easily summoned to mind, this has shades of the availability bias. It also resembles familiarity bias, insofar as Meno is uncritically privileging the verbal packaging he knows best. But there’s also a third element at play: it’s unclear whether Meno is attracted only by the familiarity of the language or also by its grandiose prolixity. If it’s the latter, this is also a case of what is sometimes called ‘proof by verbosity’, the appeal of which helps to explain why students who write longer responses on standardised tests get higher scores.

Attributing any particular instance of this sort of error to either a cognitive or ethical shortcoming is difficult. Plato doesn’t depict Meno as an incorrigible snob; he actually behaves much better than another character in the dialogue, Anytus, who becomes enraged with Socrates and threatens him. But imagine a spectrum of susceptibility to fancy yet vapid language. While intelligence might provide some protection against the seductions of such words, a lack of pretentiousness would also be an asset. Like overconfidence, pretentiousness has a moral valence. Avoiding it is not only a matter of debugging some glitch in our mental software, it’s a moral achievement.

The dialogues of Plato and ancient philosophy in general examined many of the same phenomena as modern behavioural economics. Noticing these continuities is a useful exercise in the sort of humility that helps us avoid committing some of the fallacies that both fields study. The framework of ancient philosophy also introduces a moral dimension that might be relevant to guarding against certain biases. In his essay on the modern, Russell was describing a sort of mental illusion of novelty. But his tone also had an old-fashioned moral edge: ‘We imagine ourselves at the apex of intelligence, and cannot believe that the quaint clothes and cumbrous phrases of former times can have invested people and thoughts that are still worthy of our attention.’