In the series of extracts that I am running from my almost-finished book on the history of moral thought, I have reached Chapter 12, ‘Passion, Duty and Consequence’. Chapter 11 explored some of the ideas of the Radical Enlightenment. Chapter 12 turns its gaze more on to the moral arguments that emerged from the mainstream Enlightenment – in particular the work of Hume, Kant, Bentham and Mill. This extract is from the section on David Hume.

In every system of morality, which I have hitherto met with, I have always remark’d, that the author proceeds for some time in the ordinary way of reasoning… when all of a sudden I am surpriz’d to find, that instead of the usual copulations of propositions, is, and is not, I meet with no proposition that is not connected with an ought, or an ought not. This change is imperceptible; but is however, of the last consequence.

So wrote David Hume almost as an afterthought in his Treatise on Human Nature. An afterthought it may have been, but there is arguably no single paragraph that has more resonated through modern ethics. Hume’s famous distinction between is and ought – between the world as it exists and the world as we would wish it to be – and his wrenching apart of the realm of facts and the realm of values has not only indelibly stamped itself upon modern ethical debates but has established one of the key distinctions between modern and ancient ethics. Many have come to read Hume as meaning that ought cannot be derived from is, that values do not derive from the facts of the world. That, as we shall see, was neither Hume’s likely intention nor the necessary consequence of his argument. Nevertheless from Hume comes one of the defining feature of modern ethics: the separation of facts and values.

David Hume was born in 1711 into minor Scottish nobility. At 12 he went to Edinburgh University to study literature and philosophy. He trained as a lawyer before trying his hand in commerce with a sugar company. Neither life suited him. So he took himself off to France where, for three years, he lived in La Fleche. There, in the library of the Jesuit college at which Descartes had been educated, Hume wrote his first work, A Treatise of Human Nature. He published the book on his return to England, but was deeply disappointed with the reception. ‘It fell dead from the presse’, he later wrote in his autobiography. So dissatisfied was Hume with both the reception and what he regarded as the defects of his own style of writing, that he rewrote parts of the Treatise in a more popular fashion, publishing them as An Enquiry Concerning Human Understanding and An Enquiry Concerning the Principles of Morals, and even took out a newspaper advertisement beseeching readers to ignore the original, and read the later works. But whatever the immediate reaction, the Treatise came in subsequent centuries to be seen as perhaps Hume’s most important work, and one that helped define his approach to knowledge and to morality.

Like Spinoza’s Ethicsthe Treatise opens with a discussion of the character of reality and of mind, moves on to explore the psychology of the passions, and concludes with a consideration of morality derived from his understanding of reality, mind and the passions. But whereas for Spinoza reason, will and the structure of the cosmos were the keys to comprehending morality, for Hume it was the structure of the mind and the nature of the passions.

The Treatise was published in three volumes, the first two of which, ‘Of the Understanding’ and ‘Of the Passions’ came out in 1739 and the third, ‘Of Morals’, the following year. The aim of the work, in the words of the subtitle of the first volume was An Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects. Traditional moral philosophy, Hume wrote, had depended ‘more upon Invention than Experience’. From Socrates onwards every moral philosopher had ‘consulted His Fancy in erecting schemes of Virtue & of Happiness, without regarding human Nature’. In contrast to all this, Hume resolved to make human nature ‘my principal Study, & the Source from which I wou’d derive every Truth’. Since ‘the foundation of ethics’ is ‘a question of fact, not of abstract science’, so ‘we can only expect success by following the experimental method and deducing general maxims from a comparison of particular instances’.  Hume set out to do to the moral world what Newton had already done to the physical world – establish through reasoning from observation the fundamental laws by which that world operates. But if the foundation of ethics is ‘a question of facts’, why is Hume so seemingly concerned at philosophical attempts to derive ought from is, that is to derive ethics from facts?

In the first part of Treatise, Hume sets out to produce an account of the relationships between ideas that would mirror Newton’s account of gravitational attraction between bodies.  The most innovative and important section is the discussion of induction – the process of reasoning from the observed behaviour of entities to establish general principles that can predict the behaviour of those entities even when they are unobserved – and of causation. Humans, Hume argued, tend to look for regularity in the world and to believe in the persistence of such regularity through space and time. Over the past year the sun rose in the morning and set in evening. We assume that it will do so over the next year, too. And we assume that it will do so in Australia as well as in America, even if we have not been to either place. Humans, in other words, tend to believe that patterns in the behaviour of entities in the observed present will persist into the future, and throughout the unobserved present. But, Hume insisted, we cannot rationally justify that belief. It is not reason but natural instinct, the given way our minds work, that leads us to make such inferences.

Similarly with causation.  Just as humans have a tendency to search for regularities in the world, so they have a tendency to see the world in terms of cause and effect. However, as with inductive inference, our perception of causation is, Hume insists, a product of the way our minds work not of the external world. Hume does not deny the reality of cause and effect, but he questions what we can know of this reality. When we say ‘A causes B’ all we can mean is that B is regularly preceded by A. But to go from regularity of association to belief in causation is to take a leap of faith, to insist on something that we cannot know either empirically or through reason. Ideas of necessary causation are, as Hume puts it, ‘qualities of perceptions, not of objects, and are internally felt by the soul, and not perceiv’d externally in bodies.

What does this mean for Hume’s project of introducing ‘the Experimental Method of Reasoning into Moral Subjects’? If all human knowledge comes through observation, and yet the regularities that one observes are simply the products of the mind, and the inferences one draws from those regularities cannot logically be justified, then there can be no certain knowledge. Having begun by insisting that a true ‘science of man’ could be established only ‘by following the experimental method’ that had served the natural sciences so well, Hume, by the end of Book 1, seems to have cast into doubt the very possibility of scientific knowledge. The empiricist tradition, with its stress on the importance of sense perception as the primary source of human concepts and knowledge, had been long maturing within Western philosophy from the time of Aristotle onwards, often in opposition to the Platonist tradition that had tended to see sense impressions as inadequate and fallible and had held that there were significant ways in which concepts and knowledge are intuitively gained independently of sense experience.  In the wake of Descartes, battle was renewed between the empiricists and Platonists or, as they were now called, the rationalists.  Hume, following in the footsteps of such English-speaking philosophers as Francis Bacon, John Locke and Bishop Berkley, advanced empiricism to its logical and sceptical conclusions. If all that I know of the world I know through observation, then what can I know beyond the contents of my own mind? The ‘disastrous conclusion’ from Hume’s impeccable logic seemed to be, as Bertrand Russell put it, ‘that from experience and observation nothing is to be learnt.’ It took Immanuel Kant, the towering figure of the Enlightenment, to suggest, at the end of the eighteenth century, a possible way out of this dilemma.

Hume was, however, far more than simply the logical dead-end of empiricism. Having accepted the sceptical conclusions of empiricism, Hume set out to show that they need not indeed be ‘disastrous’.  For Hume, as the philosopher David Fate Norton observes, ‘the most important remaining task of philosophy, given these well-established and obvious conclusions, was to show how we are to get on with our lives.’ And nowhere was this more evident than in his discussion of morality.

* * * *

In the second book of the Treatise, Hume moves on to discuss the passions, or what these days we would call emotions, feelings and desires. The passions are the bridge between Hume’s scepticism and his moral ideas. Hume rescued the passions from the condescension of traditional moral philosophy, being the first major philosopher to place them at the centre of his claims about the human mind and about morality. Traditionally philosophers had been hostile to the role of passions in human life, believing them to be a burden upon reason. From Socrates to Spinoza, the passions had been seen as an irrational force to be feared and contained, for let loose they could undermine and enslave reason, the essential and defining characteristic of the human being. Even philosophers like Aristotle and Aquinas, who were less hostile to the emotions and to the physical body, thought it necessary to restrain the passions and hold them subservient to reason.

Hume not only viewed the passions as a vital and integral part of human nature, but he also attributed to them many of the functions that previous philosophers had considered to be in the province of reason – the ability to make causal inferences being only the most striking example. The importance of the passions to morality is that, for Hume, reason is impotent to produce any action. Reason is concerned with matters of fact or with mathematical relations.  Neither facts nor maths can move us to act. The passions, aroused by the prospect of pleasure or pain, are the engines that drive human deeds. Without passions we would lack all motivation and impulse even to reason. ‘Reason is and ought only to be the slave of the passions’, he insisted in one of his more notorious formulations, ‘and can never pretend to any other office than to serve and obey them.’  Whereas for Spinoza, reason is a means of transforming our desires, for Hume desires are the means of motivating reason.

The whole purpose of moral judgements is to guide our behaviour. Since reason cannot move us to action, so moral judgements cannot be the product of reason but must be the consequence primarily of the passions.  Hume does not erase reason entirely from the picture. Reason provides information, especially about how to effect the means to our ends. But it cannot set those ends. Only the passions can. Morality, as Hume put it, ‘is more properly felt than judg’d of’. From Socrates to Spinoza, moral philosophers had viewed wrongdoing as the product of ignorance, a failure of reason. Not so for Hume; reason, he believed, had nothing at all to do with distinction between right and wrong, virtue and vice.

When Hume turns in Book III of the Treatise to explore the ‘moral sense’, he introduces a new term – ‘sentiment’.  It is through sentiment that we are able to make moral evaluations of other people and their characters and to distinguish between virtues and vices. A virtue is a character trait, the disinterested contemplation of which produces approval, a vice one that elicits disapproval. Approval gives us pleasure, disapproval creates pain. Moral sentiments are the means by which humans are able to engage in such disinterested contemplation; that is, the means by which they can distinguish between right and wrong, virtue and vice.

A moral sentiment is, as Hume explains it, a complex psychological disposition. It is like a passion in that it provides motive for action. It is also more than a passion, for it involves an important element of judgment. The sentiments of moral approval and disapproval are caused by some of the operations of ‘sympathy’, which is not a feeling but rather a psychological mechanism that enables one to participate in the emotional life, and pleasures and pains, of others; today we would probably talk of ‘empathy’. Sympathy allows us to share in the pleasures and pains that are the effects of those traits that we disinterestedly contemplate. When we feel pleasure, too, we approve of that trait, and view it as a virtue. When we feel pain, we disapprove and view the trait as a vice. We approve of generosity because we can identify with the pleasure that it nurtures. We abhor malice because we, too, can feel the pain that malicious action can cause.  Virtue, Hume writes, is ‘whatever mental action or quality’ of another that ‘gives to a spectator the pleasing sentiment of approbation’.  Judgments about virtues and vices become resolved, therefore, into experiences of pleasures and pains.

Not every action or person that gives us pleasure is, of course, necessarily virtuous.  Cocaine might give an addict pleasure. A sadist might find pleasure in inflicting pain upon others. And most of us might find it pleasurable to stay in bed all day or painful to have to put in a full day’s shift. So how do we distinguish those pleasures that are virtuous and those that are merely hedonistic? By judging them pleasurable or painful from a disinterested viewpoint, argues Hume.  Through the mechanisms of sentiment and sympathy, we view pains and pleasures not simply from a subjective viewpoint, but also from the viewpoint of common humanity. A disinterested view of pain or pleasure could, however, apply equally to aesthetic as to moral and judgements. There is little in Hume’s argument that allows us to distinguish between morality and taste.  Subsequent philosophers came, indeed, to view morality as a kind of statement of taste.

At the same time the idea of a ‘disinterested’ view suggests possibility of objective criteria for evaluating pleasure and pain, and hence virtue and vice.  These may be criteria rooted in human nature or in the structure of the society. If that is the case, why then cannot reason evaluate vice and virtue?  Or, to put it another way, if there are objective criteria for evaluating good and bad, criteria rooted in the facts of the world, both natural and social, should we not accept that values, in some sense at least, do derive from facts?  The contemporary neurophilosopher Patricia Churchland, who believes that morality is ‘a scheme for social behaviour that is shaped by interlocking brain processes’, argues in her book Braintrust, that while Hume ‘had no truck with simple, sloppy inferences’, he was a naturalist who acknowledged that the roots of morality lay ‘in how we are, what we care about, and what matters to us – in our nature.’ Hence, he would have accepted, and indeed did accept, that we can infer what we  ought to do by drawing upon the facts of the world as it is. Hume, in other words, has been read in highly contradictory ways.  For some he looked upon morality as a form of subjective taste.  For others he viewed it as a phenomenon rooted in objective facts.

‘No action, Hume argued, ‘may be virtuous or morally good, unless there be in human nature some motive to produce it distinct from the sense of its morality’.  Some virtues, he believed, are natural in the sense that they are embedded as dispositions embedded in human nature. These include benevolence, generosity, clemency, moderation, temperance and frugality. Every human being, Hume suggests, from primitive times to the present, have been motivated by these characteristics. Such dispositions produce good on each occasion of their practice and are on every occasion approved of.

Other virtues, however, are not natural but artificial, not traits embedded in human nature but behaviours and rules created and developed through human history.  Whereas natural virtues are always good – there are no instances Hume can imagine in which benevolence or generosity is not beneficial either to the individual or to society – and always win approval, artificial virtues are not necessarily always good or acclaimed. The most important of the artificial virtues is justice. In primitive society, Hume argues, people were motivated to act with benevolence and generosity but had no need for rules of justice, natural dispositions being sufficient to maintain order in small, kinship-based units. But as societies grew larger and more complex, and as certain goods came to be in short supply, so they began to recognize that their interests would be best served by a form of co-operation that led to the development of conventions and rules that now we call justice.  What began as a purely self-interested concern that the rules of justice be followed becomes over time, largely through the mechanism of sympathy, a moral concern for the welfare of others. Sympathy leads us to feel pleasure in response to any act that maintains the system of justice, and hence promotes the public good, and to feel pain in response to actions that break the rules of justice and endanger the welfare of others. The ‘distinction betwixt justice and injustice’, Hume writes, is built upon ‘two different foundations, viz that of self-interest, when men observe that ‘tis impossible to live in society without restraining themselves by certain rules, and that of morality, when this interest is once observed to be common to all mankind, and men receive a pleasure from the view of such actions as tend to the peace of society, and an uneasiness from such are as contrary to it.’  Through his artificial virtues, Hume marries Aristotle and Hobbes, virtue and self-interest.

For Hume, then, moral duties and obligations cannot be rationally deduced from purely factual premises. Hence the failure of much traditional moral philosophy that sought through reasoned argument to deduce ought from is.  He does not argue, however, that values cannot derive from the facts of the world, nor that there is an unbridgeable chasm between facts and values. Distinctions between good and evil, right and wrong, were, for Hume, the products not of reason but of a moral sense. But moral sense was itself a natural disposition, an aspect of human nature. Indeed, Hume claims that ‘no action can be virtuous, or morally good, unless there be in human nature some motive to produce it, distinct from the sense of its morality’.

Patricia Churchland’s reading of Hume seems more appropriate, then, than that of philosophers who claim that for Hume values do not, and cannot, derive from the facts of the world. Her insistence that Hume accepted that ‘in a much broader sense of “infer” than derive you can infer (figure out) what you ought to do, drawing on knowledge, perception, emotions and understanding, and balancing considerations against each other’, and that morally, just as socially, humans could ‘figure out what to do based on the facts of the case, and our background understanding’ appears in keeping with the spirit of Hume’s argument. Whether this means that Churchland is also right in imagining that ‘morality originates in the neurobiology of attachment and bonding’, and in the ‘oxytocin-vasopressin network in mammals [that] can be modified to allow care to be extended beyond one’s litter of juveniles’, and that neuroscience is key to understanding our moral values and beliefs, or that, as fellow philosopher Sam Harris has put it, ‘science will… decide’ between competing moral claims ‘because the discrepant answers people give to them translate into differences in our brains, in the brains of others and in the world at large’ is a different issue, and one to which I will return in the final chapter.


  1. Gabriel Andrade

    I do think Sam Harris is right. ‘Good’ is basically pleasure, ‘bad’ is basically pain. Pain and pleasure are objective facts, and scientists can tell us about it. Emotions are not mere subjective spooky phenomena, they come from brain states. And, in such a manner, neuroscience can, in principle, tell us what makes us happy and what doesn’t. To be happy is to have X neuron fire. If you are a materialist (as I assume you are, and you should be), then you must agree that every mental state has a cerebral correspondence. Thus, mental states of happiness must correspond to some brain states. And, brain states are facts, not mere values.

  2. I think you are definitely on the right track here… I look forward to reading bits from you final chapter.

    It seems to me that many use Hume to waive off criticisms about particular theories about human nature: “we’re not telling you how it OUGHT to be, we’re telling you how it IS.” Evolutionary psychologists seem to do a fair bit of that.

  3. An excellent summary of Hume’s moral philosophy – and one which wisely avoids the whole was-he-an-atheist? (probably not) question, which always provided such a misleading starting point when I studied Hume as a student. There is more to the Scottish Enlightenment – and to these ideas – than just Hume, however, as his thought had its origins in Hutcheson’s philosophy and he also collaborated with Adam Smith. I look forward to your final chapter, Tychy.

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