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This article argues that it is a waste of time seeking to treat populists as examples of homo economicus when seeking to persuade them that the conspiracy theories to which they subscribe are big lies. But it does not follow that homo economicus is worthless in this context. He has a role in explaining the evolution of the social norms whose violation is the root cause of the rise of populist movements. Such an approach requires a willingness to entertain both proximate and ultimate explanations of human behaviour simultaneously.

This paper proposes a radical alternative to discounting utility streams that allows each payoff in a stream to be treated equally. It is based on the psychology of how humans perceive time—not as the objective clicking of time on a clock—but in terms of the incidents to which attention needs to be paid. The paper’s conclusions receive some support from the discovery of the Peak-End Rule, in which laboratory subjects recall only the worst and the last experience during painful episodes.

SUMMARY Competition for social influence is a major force shaping societies, from baboons guiding their troop in different directions, to politicians competing for voters, to influencers competing for attention on social media. Social influence is invariably a competitive exercise with multiple influencers competing for it. We study which strategy maximizes social influence under competition. Applying game theory to a scenario where two advisers compete for the attention of a client, we find that the rational solution for advisers is to communicate truthfully when favoured by the client, but to lie when ignored. Across seven pre-registered studies, testing 802 participants, such a strategic adviser consistently outcompeted an honest adviser. Strategic dishonesty outperformed truth-telling in swaying individual voters, the majority vote in anonymously voting groups, and the consensus vote in communicating groups. Our findings help explain the success of political movements that thrive on disinformation, and vocal underdog politicians with no credible program.

This commentary on the paper “Knowledge before belief” argues that it is not only in the cognitive sciences that knowledge should be separated into a separate category from belief, but also in rational decision theory. It outlines how knowledge-as-commitment – as distinct from knowledge-as-belief – can be built into an extension of the economic theory of revealed preference.

Epicurus (341–270 BC) first came to Athens from the island of Samos when he was 18 to serve the military apprenticeship necessary to retain his Athenian citizenship. Xenocrates was then the third head of the Academy; Aristotle was still alive but in retirement abroad. Epicurus was a follower of the down-to-earth philosophy of Democritus of Abdera, of whom we heard earlier as the mentor of Protagoras. As such, he was a life-long opponent of Plato, against whose ideas he rebelled at the tender age of 14. Although his origins were humble, Epicurus eventually established a philosophical school in Mytilene on the island of Lesbos, but he and his followers were expelled as a result of the civic unrest to which their teachings apparently led. The school moved to Lampsacus, where he acquired Metrodorus as a friend and disciple, and then to Athens. In Athens, Epicurus bought a house with a walled garden—on the road from the Agora to the Academy—where he established a school called the Garden set up in explicit opposition to Platonism. Perhaps as a result of his unpleasant experiences in Mytilene, his followers in Athens played little or no role in Athenian social and political life.

Logical positivism is an extreme variety of empiricism which holds that all propositions that cannot be verified through direct observation or logical proof are without meaning. It ourished in the 1930s, when its chief proponents were known as the Vienna Circle, whose leading member was arguably Rudolph Carnap.

This imaginary dialogue is perhaps the least likely of several unlikely meetings yet to come. St Augustine (354–430 AD) was Bishop of Hippo in North Africa, when it was still part of the Western Roman Empire, although he died while it was under siege by the Vandals, to whom it eventually fell. Rome itself had already been sacked by the Visigoths, which led to Augustine writing his famous City of God—with its foul doctrine of original sin—to explain that Rome may fall, but the domain of God is not of this world.

Plato and Aristotle are the two great figures of western philosophy. Raphael’s famous painting—used as a cover for this book—shows them surrounded by the intellectual elite who followed in their footsteps down the ages. It is therefore close to hubris to imagine a dialogue between them, especially since it covers only one small aspect of their contributions to philosophy. Raphael’s picture indicates the issue they discuss by showing Plato gesturing at the heavens above, while Aristotle focuses on the earth below. The Aristotle of my dialogue fits this paradigm, but the real Aristotle resists all attempts at classification. He was a polymath, whose work ranges across the whole range of philosophical enterprise. The practical, scientific line of questioning attributed to him in the dialogue is only one aspect of a life of intellectual endeavor that escapes any attempt to tie it down. It is breathtaking to learn that it is only by a fortunate chance that his many surviving books came down to us intact.

Von Neumann and Morgenstern's 1944 Theory of Games and Economic Behavior was initially thought to herald a revolution in economic theory, but disillusion soon set in when it was realized that only zero-sum games were adequately covered. John Nash redirected the subject in a more profitable direction by focusing attention on what came to be known as a Nash equilibrium, although it took more than twenty years before economists were willing to pay attention to game theory again.

Descartes and Hobbes are said actually to have met face-to-face in 1647 or 1648. It must have been a bad-tempered occasion if Descartes’ written replies to Hobbes’ objections to his famous Meditations are any guide. Hobbes is seriously rude and Descartes responds with contempt. Descartes says somewhere else that Hobbes is “aiming to make his reputation at his expense, and by devious means”.

The obsessive affair between Jean-Paul Sartre and Simone de Beauvoir provided copy for French newspapers for more than fifty years.

Matthew Stewart’s The Courtier and the Heretic already offers speculations about what went on when Leibniz and Spinoza actually met over a three-day period in 1676. My imaginary dialogue is less ready to condemn Leibniz. His urge to excel admittedly makes him a less attractive character than Spinoza, but his willingness to follow arguments wherever they may go is surely worthy of our respect.

Charles Darwin spent his final years at Down House, a country residence only sixteen miles south of central London. Down House is maintained today as a museum in Drawin’s honor.

John Rawls is regarded as the leading moral philosopher of the twentieth century. His Theory of Justice is a counterblast against utilitarianism that redirected political liberalism onto a new path. His continuing success in reaching hearts and minds is even enshrined in an all-singing, all-dancing musical A Theory of Justice: The Musical!, which had some success in the UK in 2013. Rawls’ basic idea is that justice is no more than fairness, which is to be judged using the “original position” in which we imagine ourselves behind a “veil of ignorance” that conceals our identities from ourselves while we bargain our way to solutions to our social problems.

Various accounts of a 1946 meeting between Popper and Wittgenstein appear in a lively book called Wittgenstein's Poker by David Edmonds and John Eidinow.

The American War of Independence and the subsequent French Revolution form the background to an imaginary dialogue between Tom Paine and Edmund Burke. They exchanged inflammatory books and pamphlets that were lapped up by the general public of three nations, but it seems that they never met. Some creativity is therefore necessary to get them together, but the story that locates them both at a dinner hosted by William Godwin in 1791 is more plausible than the stories invented to justify several of the earlier dialogues.

Immanuel Kant is commonly said to be the greatest philosopher ever, having supposedly rescued rationalism from an empiricist assault reaching its peak in the work of David Hume. Kant was certainly inspired by Hume, whom he credited with waking him from his “dogmatic slumber”, but it stretches the imagination too far to suppose that an elderly and ailing Hume would have somehow found his way to the Prussian city of Konigsberg long before Kant's philosophical ideas had been acclaimed as the culmination of the Enlightenment. However, as a fellow Scot, Hume acted as mentor to Adam Smith, both in economics and in philosophy. It is still a very considerable stretch to get Adam Smith to Konigsberg (modern Kaliningrad), but perhaps not such a stretch as getting St Augustine to Alexandria while the western Roman Empire was collapsing around his ears.

Jeremy Bentham and John Stuart Mill were thorough-going empiricists. They are jointly credited with inventing utilitarianism, although Bentham gives priority to the Swiss philosopher Helvetius. It is usually said that Mill provides the intellectual underpinnings for utilitarianism that Bentham neglects, and it is true that Bentham was brutally honest in identifying points in his theory where crucial assumptions are made without adequate foundations. What is utility? Why maximize your utility? How is your utility to be compared with mine? Why should society not maximize some other function of everybody’s utilities rather than their sum? The world had to wait for John Harsanyi for coherent answers to these questions. Mills’ contribution was rather to round off the rough edges of Bentham's exposition to make his theory acceptable to the intellectual elite of his time. However, orthodox opinion nevertheless credits him with being the leading exponent of naturalist philosophy in the nineteenth century.

Hume and Rousseau most certainly met. In fact, their meeting became a sensation in philosophical circles after Rousseau accused Hume of black treachery, and Hume—who was guilty at worst of participating in some horseplay involving a spoof letter from Frederick the Great—responded in an undignified way. However, their imaginary dialogue occurs some time before all this unpleasantness. It takes place in a cabin on a cross-channel ferry that Hume and Rousseau shared after Hume undertook to look after Rousseau in England, where Rousseau had eventually decided to live after being exiled from France.

Marcus Aurelius (121–180 AD) was the last of Edward Gibbon’s five good emperors of Rome. He left behind a fascinating book called the Meditations in the form of notes to himself on how better to conform to the Stoic principles that he espoused. Although he is counted as a philosopher, he had nothing new to offer beyond the thoughts of the great Epictetus, for whom I cannot find a worthy partner. Cicero and Seneca are much quoted as earlier Roman Stoics, but I find Cicero too smug, and Seneca too dishonest for inclusion.

John Locke is sometimes said to be the founding father of empiricism. He is certainly one of three philosophers who make up the traditional British school of empiricists, of whom the other two are Bishop Berkeley and David Hume. (I do not know why Hobbes is omitted from this list, nor why he is similarly omitted from the list of Locke, Rousseau and Kant, who are always mentioned as the primary social contract theorists.) However, the ancient philosophers, Democritus and Epicurus, were much more thorough-going empiricists than Locke.

The preceding dialogue between Harsanyi and Rawls took place in Normandy, where they are imagined to have both own from America to receive honorary doctorates from the University of Caen. In real life, Rawls was unable to come, having been struck down by the first of a number of strokes that largely confined him thereafter to his bed. Our next imaginary dialogue is similarly unrealistic in assuming that he is sufficiently well to receive Derek Parfit in his sickroom some years later. Parfit is hoping to get some endorsement from Rawls of his interpreting Rawls’ Theory of Justice as a defense of a moral principle that Parfit calls prioritarianism.

People sometimes say that Ludwig Wittgenstein was the greatest philosopher of the twentieth century. He is credited with having made important contributions to logic, the philosophy of mathematics, and the philosophy of language.

Plato (429–347 BC?) was a scion of the aristocratic elite of ancient Athens. He founded the Academy to maintain the philosophical tradition of Socrates (470–399 BC?) of whom he was a fervent admirer. All of his written work is believed to survive, nearly all of which is in dialogue style with Socrates as the leading speaker. As in the Protagoras, the early dialogues are thought to be fictionalized accounts of genuine encounters between the real Socrates and a wide spectrum of debating partners, ranging from Parmenides, who instructs him on the nature of being and not-being, to Euthyphro, who is no competition at all. However, the later dialogues feature an invented Socrates, who arguably becomes merely a mouthpiece for Plato’s own opinions. Diogenes (404?–323 BC) is the philosopher who famously lived in a barrel, and made fun not only of Plato’s pretensions at having penetrated the mysteries of the universe, but of the conventions of normal life in the Athens of his time. He apparently made a show of his contempt for the system of rewards and punishments with which societies sustain such conventions, by openly defying them. He is said, for example, to have publicly masturbated in the Agora.

There was a famous debate between Bertrand Russell and John Dewey in the early twentieth century. It was ostensibly about how children should best be educated. Both men had helped their wives run experimental schools, and then used their philosophical careers as platforms from which to preach their favored methodologies. Looking back on their debate from a hundred years in the future, it is their similarities rather than their differences that strike the eye. So what generated their sometimes heated exchanges? It is usually thought to be their attitude to truth.

Peter Abelard (1079{1142) is remembered nowadays largely because of his scandalous love affair with his pupil Heloise. (She was not only lovely to look at, but later revealed an intellect arguably a match for his own.) However, her uncle and guardian was outraged at Abelard's betrayal of his trust. He took his revenge by sending a bunch of roughnecks to break into Abelard's lodgings, and castrate him. Abelard survived, but was later brought low by accusations of heresy from the many enemies he had made in a meteoric career, in which he came from nowhere to be regarded as the foremost logician of his times. He was apparently one of those aggressive folk who cannot control their urge to show how much cleverer they are than everybody else.

Our first imaginary dialogue sets the scene for the whole book by retelling Plato’s account of a meeting in ancient Athens between a youthful Socrates and the ageing sophist Protagoras. My version of their debate is a lot more fictional than Plato’s, although experts argue that Plato’s Protagoras must also be fictionalized to some extent, since the historical evidence suggests that the audience of distinguished intellectuals who supposedly listened to the debate could not all have been in Athens at the same time. Since the issues discussed are only loosely connected, perhaps Plato joined together several accounts of meetings between Socrates and Protagoras.

Karl Popper and Imre Lakatos became my colleagues at the London School of Economics when I joined its new Mathematics Department in 1969. Both are leading names in the philosophy of science. At that time, Popper was sometimes said to be the greatest living philosopher.

John von Neumann's 1928 invention of game theory was just a sideline for him. It remained unappreciated until the economist Oskar Morgenstern persuaded him that they should write a book together that was eventually published as The Theory of Games and Economic Behavior in 1944.

There is no problem in finding an occasion for Marx and Engels to meet in 1846. Although their first meeting in 1842 did not go well, they eventually became close collaborators, meeting many times when both were living in Brussels between 1845 and 1848. Marx was then editing a radical newspaper, in which he published an essay by Engels on the current state of what was then called Political Economy. The essay apparently persuaded Marx to adapt his ideas on economics to the approach advocated by a new wave of British economists led by Adam Smith (1723?–1790) and David Ricardo (1772–1823). This decision to use models in which people supposedly act in their own enlightened self-interest was highly significant for Marxian theory, but what Engels and Marx talk about mostly in their imaginary dialogue is the labor theory of value that Engels thinks they should borrow from David Ricardo.