The best books are those that tell you what you already know, but didn’t know that you knew.
Short introduction video (90s)
Find out more about the Ataraxia and Ancient Wisdom series—and about me.

The best books are those that tell you what you already know, but didn’t know that you knew.
Short introduction video (90s)
Find out more about the Ataraxia and Ancient Wisdom series—and about me.
What if depression were a blessing as well as a curse? This is a book about how depression can have benefits as well as costs, and how to reap those benefits while making yourself feel better—better, in fact, than ever before.
🏆 Semi-finalist, the BookLife Prize
🏆 Highly Commended, the BMA Book Awards
A comprehensive, sympathetic, and thought-provoking guide for those who want to explore their depression in more depth. —The British Journal of Psychiatry
This book brings understanding and encourages independent solutions. It is remarkable in its shortness and practicality. —The British Medical Association Book Awards
★★★★★ I have read most of Dr. Neel Burton’s books and have enjoyed them immensely … All in all, I found this to be a very insightful and engaging book on depression. —Jamie Bee, Amazon.com Top 50 Reviewer
Grab your copy now for a new and powerful way of looking at depression.

Kissing is not universal among human beings and, even today, there are some cultures that have no place for it. This suggests that the behaviour is not purely innate or intuitive, as it may seem to us, but culturally shaped and historically variable—one of the ways in which human beings negotiate the boundary between self and other.
It could be that kissing is a learnt behaviour that developed from ‘kiss feeding’, the process by which mothers in some cultures feed their infants by passing masticated food from mouth to mouth. Yet, there are some present-day indigenous cultures that practise kiss feeding but not social kissing. Another possibility is that kissing is a culturally determined form of grooming behaviour, or, in the case of deep or erotic kissing, a representation of, substitute for, and complement to penetrative intercourse.
Whatever the case, kissing behaviour is not specific or unique to human beings. Primates such as Bonobo apes frequently kiss one another; dogs and cats lick and nuzzle one another and members of other species; even snails and insects engage in antennal play. It could be that, rather than kissing, these animals are in fact grooming, smelling, or communicating with one another, but even so, their behaviour implies and strengthens trust and bonding.
Vedic texts from Ancient India seem to talk about kissing, and the Kama Sutra, which probably dates back to the second century CE, devotes an entire chapter to modes of kissing. Certain anthropologists have suggested that the Greeks learnt about erotic kissing from the Indians after Alexander the Great invaded India in 326 BCE. But even if true, this need not mean that erotic kissing originated in India, or that it does not predate the oral roots of the Vedas.
In Homer’s Iliad, which dates back to the ninth century BCE, King Priam of Troy memorably kisses the hand of Achilles in pleading for the return of Hector’s defiled corpse:
Fear, O Achilles, the wrath of heaven; think on your own father and have compassion upon me, who am the more pitiable, for I have steeled myself as no man yet has ever steeled himself before me, and have raised to my lips the hand of him who slew my son.
In the Histories (fifth century BCE), Herodotus speaks of kissing among the Persians, who greeted men of equal rank with a kiss on the mouth and those of slightly lower rank with a kiss on the cheek. Herodotus reports that, because the Greeks ate of the cow, which was sacred to the Egyptians, the Egyptians objected to kissing them on the mouth.
Kissing also features in the Old Testament. Disguised as Esau, Jacob deceives his blind father Isaac and steals his brother Esau’s blessing, sealing the deception with a kiss. When Jacob returns after years of exile, Esau runs to him, embraces him, falls on his neck, kisses him, and they weep. Naomi, insisting that her Moabite daughters-in-law Ruth and Orpah remain in Moab to make new lives for themselves, kisses them farewell, and they weep. Absalom wins the hearts of Israel by kissing all who come to him seeking justice. In the Song of Songs, which celebrates sexual love, a lover implores, ‘Let him kiss me with the kisses of his mouth, for thy love is better than wine.’
Under the Romans, kissing became much more commonplace. Romans kissed their partners or lovers, family and friends, and rulers. They distinguished a kiss on the hand or cheek (osculum) from a kiss on the lips (basium) and a deep or passionate kiss (suavium).
Roman kisses fulfilled a range of purposes, from the political and legal to the social and sexual. The status of a Roman citizen determined the part of the body—ranging from cheek to foot—on which he or she would be allowed to kiss the emperor. In an age of widespread illiteracy, kisses served to seal agreements—hence the ‘X’ on the dotted line, and the expression ‘to seal with a kiss.’ Couples were wed by kissing before a gathering, a practice that carries on to this day.
Roman poets such as Catullus and Martial treat erotic kissing as something far removed from sentimental delicacy. Kissing is intensely physical, emotionally charged, and often unsettling in its implications.
In Catullus, kisses emerge within the turbulence of erotic attachment and jealousy, where intimacy is inseparable from fear of loss and replacement. ‘Who will you kiss? Whose lips will you bite?’ is not celebratory, but a bitter imagining of desire redirected elsewhere.
In Martial, kissing becomes more explicitly corporeal and public in character, sometimes figured as excessive or intrusive—an act that overwhelms the boundaries of the self and edges into domination or comic excess.
Across both poets, kissing is less a gentle emblem of love than an occasion in which desire becomes unstable, contested, and materially insistent. In short, in Roman poetry, kissing is not a symbol of love so much as one of its problems.
Customs changed with the decline of Rome. Early Christians often greeted one another with a ‘holy kiss’, which was believed to lead to a transfer of spirit. The Latin anima means both ‘breath of air’ and ‘soul’, and, like animus [mind], comes down from the Proto-Indo-European root ane- [to breathe, blow]. Although St Peter had spoken of the ‘kiss of charity’, and St Paul of the ‘holy kiss’, early Christian sects omitted kissing on Maundy Thursday, the day of the year on which Judas betrayed Jesus with a kiss. Outside of the Church, kissing was used to cement rank and social order, for instance, subjects and vassals kissed the robe of the king, or the slippers or ring of the pope.
After the fall of Rome, the romantic kiss (as distinct from other types of kiss) becomes less prominent in surviving literature for several centuries, before re-emerging in new forms with the rise of courtly love from the late eleventh century. The kiss in Romeo and Juliet is emblematic of this long cultural trajectory, which sought to remove courtship from the purview of family and broader society and celebrate romantic love as a liberating, self-determining, and potentially subversive force.
The fate of the star-crossed lovers reminds us that such carefree abandon is not without risk, and it may be that vampirism evolved as a representation of the dangers—to health, rank, reputation, prospects, and happiness—of crossing too easily between selves.
Neel Burton is author of Heaven and Hell: The Psychology of the Emotions.

For centuries, the West rested on a stable psychological foundation, with human beings firmly at the center of a purposeful cosmos.
The geocentric system of Aristotle and Ptolemy, in which the Sun, stars, and planets revolved around a fixed and unmoving Earth, did more than describe the heavens. It organised meaning. Humanity occupied a privileged position in creation, and the structure of the universe seemed to confirm it.
The Copernican Revolution shattered that certainty. Yet its significance was never merely astronomical. It was psychological. It obliged human beings to confront the unsettling possibility that we are not as central as we imagine.
That confrontation did not end with astronomy. Over the following centuries, humanity would endure a succession of intellectual revolutions, each removing another claim to exceptional status. The same drama may now be unfolding once again with artificial intelligence (AI).
The parallels begin with resistance. Nearly eighteen centuries before Copernicus, Aristarchus of Samos proposed that the Earth moved around the Sun. Anaxagoras similarly suggested that the Sun was not a divine object but another celestial body. Yet neither transformed humanity’s understanding of itself.
The obstacle was not a lack of evidence alone. Human beings are not neutral observers of reality. We are psychologically invested in narratives that place us at the center of events, and we resist discoveries that threaten that position.
The same tendency shapes our response to AI. The possibility that machines might perform tasks once regarded as uniquely human has been dawning for decades. Yet many people continue to regard intelligence as an exclusively human possession. As with heliocentrism, the deepest resistance is not empirical but existential. What is at stake is not merely a theory of intelligence, but humanity’s place within it.
When, in 1543, Copernicus published On the Revolutions of the Heavenly Spheres, he displaced the Earth from the center of the universe.
The first response was not acceptance but compromise. Tycho Brahe proposed a hybrid system in which the planets orbited the Sun while the Sun itself continued to orbit the Earth. The new evidence was accommodated without fully abandoning the old hierarchy.
We often respond to AI in a similar fashion. We describe it primarily as a tool, an assistant, or an extension of human agency. These descriptions are true in practical terms. Yet they may also serve a psychological function, allowing us to absorb the implications of machine intelligence without fundamentally reconsidering humanity’s place within the cognitive landscape.
Like Tycho’s system, such interpretations preserve the familiar hierarchy while making room for disruptive facts.
Genuine revolutions require deeper adjustments.
Kepler provided one by replacing perfect circles with elliptical orbits governed by mathematical laws. This was more than a technical refinement. It represented the abandonment of a profound assumption: that reality must conform to human intuitions of beauty, symmetry, and perfection.
The universe no longer reflected what human beings wished to see. It followed impersonal principles.
We often anthropomorphise AI in the opposite direction, imagining it as a digital version of ourselves. Yet its operation is fundamentally unlike human thought. Contemporary AI systems identify patterns across immense quantities of data using methods that frequently defy human intuition. Their successes emerge not because they think as we do, but because they often do not.
Like Kepler’s ellipses, their effectiveness can be unsettling precisely because it does not conform to our expectations.
Galileo’s telescope deepened the rupture.
Mountains on the Moon, moons orbiting Jupiter, and countless previously unseen stars revealed that the heavens were neither perfect nor organised exclusively around the Earth. The cosmos appeared populated by multiple centres, multiple systems, and multiple worlds.
Today, AI may be producing a comparable shift in our understanding of cognition. For centuries, language, reasoning, and creativity were treated as evidence of humanity’s unique status. Increasingly, these capacities appear capable of emerging in different substrates and systems.
This does not necessarily mean that machine intelligence and human intelligence are identical. Yet even the appearance of machine cognition exerts a decentring effect. It forces us to confront the possibility that intelligence may not be an exclusively human phenomenon.
Giordano Bruno carried the implications of heliocentrism beyond anything Copernicus himself proposed.
He imagined an infinite universe populated by innumerable worlds. In such a cosmos, humanity lost not merely its central location but the very idea that any location could be central.
The significance of Bruno’s vision was philosophical as much as astronomical. If there are countless worlds, then no single perspective can claim cosmic privilege.
Today, something similar may be occurring in our conception of intelligence. The traditional hierarchy that places human cognition at the apex of all thinking systems is giving way to a more distributed landscape of minds, algorithms, networks, and machine systems.
The challenge is not simply that machines perform cognitive tasks. It is that intelligence itself may be a broader and more varied phenomenon than previously imagined.
By the time of Newton, cosmological decentring was largely complete.
Heaven and Earth were unified within a single system of mathematical relationships. The same laws that governed orbiting planets governed falling apples. Reality no longer revolved around human purposes but operated according to indifferent principles.
Just as Newton dissolved the distinction between the terrestrial and celestial realms, AI may be eroding the distinction between human and machine cognition. Capacities once regarded as uniquely human increasingly appear to be manifestations of more general informational processes.
Yet human psychology has not evolved nearly as quickly as human knowledge. We remain creatures who seek significance, narrative, and reassurance. Newton himself devoted enormous energy to alchemy and theology.
The desire for meaning survived the collapse of geocentrism. It survived Darwin and Freud as well. It will survive the rise of AI.
After the Copernican Revolution, meaning could no longer be derived from occupying a privileged position in the cosmos. Meaning had to be created rather than discovered.
Now, we may have to learn this lesson anew. If intelligence is not uniquely human, then our value cannot rest on exclusivity. It must rest on how we choose to live, create, relate, and act within a reality that no longer upholds our physical and mental centrality.
The Copernican Revolution was the beginning of a long psychological transition: from a world organised around humanity to a world that simply is. The AI Revolution is simply the next stage in that journey.
Nietzsche would have recognised this moment. Copernicus removed humanity from the center of the cosmos; AI is removing it from the center of intelligence. Nietzsche argued that maturity begins when we stop demanding a privileged place in reality and instead create meaning for ourselves.
The question raised by AI is therefore not whether we remain special, but whether we can flourish without being the center of everything.
Neel Burton is the author of the newly published The German Greeks: German Philosophy and the German Philosophers.

In 1781, after a decade of introspection, Immanuel Kant published a book so difficult that even leading philosophers struggled to finish it. Kant’s friend and rival Moses Mendelssohn described the Critique of Pure Reason as a “nerve-juice consuming book.” Yet, buried within its more than 800 pages is one of the most influential ideas in the history of thought—an idea that Kant himself compared to the revolution begun by Copernicus in astronomy.
Previously, everyone believed that the Sun revolved around the Earth. Copernicus (1473-1543) turned the tables by asking how it would be if, instead, the Earth revolved around the Sun. Kant believed that human thought itself required a similar reinvention. It had always been assumed that human knowledge must conform to the world, that the human mind was just a passive observer. But what if it was the other way round? What if it was the world that needed to conform to the structures of the human mind?
Since Descartes (1596-1650), a debate had been dominating philosophy. On one side stood the rationalists such as Descartes, Spinoza, and Leibniz, who believed that the senses were deceptive and that reason was the only secure source of knowledge. On the other side stood the empiricists, especially Locke and Hume, who argued that the mind starts as a blank slate and that all knowledge is founded in sense experience.
Hume (1711-1776) pushed the empiricist position to its logical conclusion, which is that there are only two kinds of human knowledge: “matters of fact”, which are founded in observation, and “relations of ideas,” such as logic and mathematics, which are true by definition. Anything that is neither, including God, the soul, and free will, belongs to the realm of illusion and speculation.
This scepticism deeply troubled Kant. Hume’s position undermined many of the concepts on which science and social life depend, not least causation. We assume that causes produce effects, but never—according to Hume—observe causality itself: all we do is observe one event regularly following another. Kant fully acknowledged his debt to Hume: “I freely confess: it was the objection [to the principle of cause and effect] of David Hume that first … interrupted my dogmatic slumber…”
Kant’s response was to seek a new foundation for knowledge, based on a distinction between different kinds of judgement.
Some statements, such as, “All bachelors are unmarried men,” are analytic, in that their truth is contained within the meanings of the words themselves. Other statements, such as, “The cat is on the mat,” are synthetic, in that they carry new information. Most of the claims that we make are synthetic, because, unless you’re a pedant like me, new information about the world is a lot more useful and interesting than tautologizing.
Kant also distinguished between knowledge that is à priori (acquired independently of sense experience) and knowledge that is à posteriori (acquired from sense experience).
Whereas analytic truths are à priori, synthetic truths are à posteriori. But could some synthetic truths be à priori? If so, we could learn something genuinely new independently of sense experience.
Kant believed that mathematics, geometry, and, indeed, causation are prime examples of synthetic à priori knowledge.
But how could reason alone provide us with new knowledge, independently of sense experience?
Kant’s answer was revolutionary. The human mind is not a passive recipient of information, but actively shapes experience.
The mind possesses built-in structures that organize raw sense data. Among these “categories of understanding” are concepts such as causality, substance, unity, plurality, and necessity.
Whenever we experience the world, these categories are already at work. They are not learned from experience; rather, they make experience possible in the first place. They package raw sense data into forms that are graspable to the human mind. If, as per Hume, we never observe causality, this is because causality is a feature of the human mind.
The same is true also of space and time, which are not features of the world, but “forms of intuition” by which the human mind organises sense experience. Space is the framework by which we perceive external objects. Time is the framework by which we order events and mental states.
That space, time, and causation are in the mind does not make them subjective fantasies. Because all humans share these cognitive structures, they provide a common framework for objective experience. Simply put, there is, for a human being, no other way of seeing the world.
So here we have it. The mind does not conform to an independently structured world; rather, the world as we experience it conforms to the structures of the mind. Thus, we can know some things about the world by knowing about our mind. This is what underlies and enables the synthetic à priori. This is, in other words, what makes it possible for reason, working outside of sense experience, to arrive at new knowledge.
Causation and mathematics arise from the very conditions that make human experience possible. But the flipside is that we cannot know what lies outside of human experience. We cannot know how the world is in itself. Unlike the phenomenal world of human experience, this noumenal world is closed to reason, science, and knowledge.
Thus, metaphysical questions about God, the soul, and freedom are outside the scope of human knowledge. Kant may have rescued causation from Hume and the empiricists, but he did not rescue God (although, later, he defended belief in God on moral grounds). He earned the nickname “the All-Crusher” because he seemed to have demolished centuries of metaphysical speculation about God, the soul, and free will, which, he thought, were outside the scope of human knowledge.
Whenever reason attempts to venture into the realm of metaphysics, it becomes entangled in contradictions. Kant demonstrated this through four specific “antinomies of pure reason,” that is, contradictions that reason falls into when trying to understand ultimate reality.
Here is my own example of an antinomy of pure reason. After more than two thousand years of debate, there is still no consensus on who made the stronger case: Heraclitus, in arguing that the universe is in constant, perpetual flux (thesis), or Parmenides in arguing that it is in fact a single, static, unchanging, and eternal whole (antithesis).
Reason, Kant noticed, can construct persuasive arguments on both sides. The resulting conflicts reveal not the failure of reason but the danger of taking it beyond its proper domain. Plato demonstrated something similar in the Parmenides, though less explicitly than Kant.
Unlike the German idealists whom he inspired (Fichte, Schelling, Hegel…), Kant did not go so far as to claim that the mind creates reality, only that the world as it appears to us is structured through the forms and categories of human cognition.
Since Kant’s time, developments in modern physics, particularly non-Euclidean geometry and Einstein’s theory of relativity, have challenged some of Kant’s specific claims about space. But his central insight continues to shape philosophy, psychology, and cognitive science.
We do not simply discover the world. We actively shape the way it appears to us. This was Kant’s Copernican revolution: the insight that knowledge is not merely a mirror of reality but the outcome of a dynamic interaction between the mind and the world. By redefining the relationship between human beings and experience, Kant transformed philosophy as profoundly as Copernicus transformed astronomy.
Neel Burton is the author of the newly published The German Greeks: German Philosophy and the German Philosophers.

When obeying those moral laws that we could consistently and rationally will as universal laws, we are following the so-called Categorical Imperative, which might be re-stated as, “Always act such that the maxim of your action can at the same time be upheld as a universal law.”
This is similar to the much older Golden Rule of the Bible and Indian Mahabharata, according to which we should treat others as we would wish to be treated. But whereas the Golden Rule is based on personal desire, which is subjective (I might, for example, be a masochist, or be willing to tolerate some mistreatment), the Categorical Imperative is based on reason, which is objective.
Hypothetical imperatives are practical rules for achieving a desired outcome, for example, “If you want to lose weight, you should watch what you eat.” If you do not desire a particular outcome, you do not need to follow the rules. In this much, hypothetical imperatives are conditional and contingent. In contrast, Categorical Imperatives are universal moral commands that bind everyone regardless of their aims, for example, “Do not lie,” “Do not steal,” “Do not commit suicide.”
Hypothetical imperatives answer to the lower faculty of desire, which aims at pleasure. Categorical Imperatives answer to the higher faculty of will, which functions rationally and autonomously by following the laws which it legislates for itself, regardless of consequences or personal feelings.
For Kant, true moral actions must be motivated by duty, not some desired outcome. Thus, Kantian ethics are sometimes described as deontological, or duty-based [Greek, deon, “duty”], and contrasted with consequentialism (for example, utilitarianism), which is outcome-based. For Kant, moral systems based on outcomes or desires operate on hypothetical imperatives, not true moral law.
Kant furnishes some examples to flesh out the bones of the Categorical Imperative. Imagine a person in financial need who borrows money and promises to pay it back, knowing full well that they never will. If this action were universalised, promises of repayment would no longer be believed and the practice of lending would end.
When we help someone, our action must be motivated by duty if it is to have moral worth. If I help someone from inclination, for example, from sympathy or because it makes me feel good, I am still doing a praiseworthy thing, but my action, being circumstantial rather than principled and reliable, lacks moral worth. Imagine a grocer who always gives the correct change, but only to avoid being caught and losing his reputation. His behaviour, though not blameworthy, is lacking in moral worth. If he knew that he could not possibly get caught, he may start behaving dishonestly. Because his behaviour is prudential and circumstantial rather than born out of duty, it is not categorical.
For Kant, a paradigm of moral worth is the person who hates life and longs to commit suicide, but stays alive purely out of duty. Because this person has no self-serving inclinations, he is acting purely from duty, rather than mere “conformity to duty.” Similarly, and counterintuitively, a hard-hearted person who has no other motivation than duty has a moral worth “beyond all comparison the highest.”
The universalizability formulation is the first formulation the Categorical Imperative. The second formulation is the humanity formulation, or end-in-itself formulation: “Act always treating humanity, in yourself and others, as an end and never merely as a means.”
Like Aristotle, Kant argued that everything that has instrumental value derives this value from the end that it serves. Thus, for anything to have value, there must be some end that has intrinsic worth, that is, some end that is an end-in-itself. For Aristotle, this “supreme good” was happiness, or eudaimonia. For Kant, it was a rational being who could freely determine his or her own ends. In all of nature, man alone is an end-in-itself, and must therefore be treated as such.
We can only use others (like waiters and cab drivers) as means if we respect their own ends and agency, treating them as rational beings with purposes of their own rather than mere tools for achieving ours. You can employ a servant if you pay and treat them fairly, and the servant wills it because working for you furthers their own ends. Although Kant never applied the humanity formulation to specifically and explicitly condemn the transatlantic slave trade, his moral philosophy provided the framework for later abolitionists.
In the aftermath of the Reign of Terror (1793-1794), a period during the French Revolution marked by mass executions of perceived enemies, the Swiss writer Benjamin Constant conceived of a thought experiment to undermine Kantian ethics.
Imagine an axe-wielding murderer at your door, asking where your friend, who has taken refuge in your house, is hiding. Although, according to Kant, lying is always wrong, it would be absurd to speak the truth and reveal your friend’s location to the murderer. In this scenario, surely, the duty to protect your friend overrides any duty to tell the truth. What’s more, by intending to commit a grave injustice, the murderer has forfeited any right to the truth.
Kant responded to Constant in his 1797 essay, On a Supposed Right to Tell Lies from Benevolent Motives, and dug in his heels. Even in those circumstances, it would be wrong to lie. The morality of an action is determined by its principles, not its consequences. One could not know whether lying would do more good than harm to one’s friend in hiding. Whereas one would be responsible for the consequences of telling a lie, the consequences of telling the truth would be on the murderer. Moreover, to lie to the murderer would be to treat him as a mere means to an end, denying him the status of a rational being capable of free, reasoned action.
Kant’s rigid application of the Categorical Imperative led him to condemn many actions and behaviours that are no longer generally condemned, such as masturbation and suicide out of world-weariness. He referred to masturbation as an “unnatural vice” on the basis that the natural purpose of sex is procreation.
The Categorical Imperative is, no doubt, a good rule of thumb, but must admit of exceptions. Exceptions, too, are a matter of judgement and reason—more so even than the rules themselves.
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