In the introduction to his Treatise of Human Nature, David Hume (1711–1776) describes the intellectual scene before him as a “noise and clamour” in which every trivial question was debated, but nothing important ever settled. Hence arose “a common prejudice against metaphysical reasonings of all kinds, even among those, who profess themselves scholars.” Thinkers such as Descartes, Locke, and Berkeley had apparently succeeded in undermining the basis of our basic beliefs about the world, but had not succeeded in erecting anything substantial in their place. Hume is rightly counted among the great philosophical skeptics, yet his primary aim is not destructive. His philosophical project, as he saw it, was to establish a new foundation for philosophy on the ground cleared by skepticism.

The foundation was to be provided by a new science of human nature based on experience and observation. The full title of his first book is A Treatise of Human Nature: Being an Attempt to Introduce the Experimental Method of Reasoning into Moral Subjects. For Hume, the science of human nature was like a capital city from which, once captured, we might “extend our conquests over all those sciences, which… concern human life.” He describes his method as “experimental” and he sees himself as applying the methods of Isaac Newton and Francis Bacon to moral subjects. However, since these subjects are not susceptible to controlled experiments, Hume urges that “we must glean up our experiments in this science from a cautious observation of human life, and take them as they appear in the common course of the world, by men’s behaviour in company, in affairs, and in their pleasures.” Experience and observation, according to Hume, were the only bases of the moral sciences as for the natural sciences, and he refused to draw any conclusion that could not be confirmed by them.

Human Nature and Causation

Hume begins from our “perceptions,” the basic elements of human experience. These divide into “Impressions,” which “comprehend all our sensations, passions and emotions, as they make their first appearance in the soul”; and “Ideas,” which are “the faint images of these [impressions] in thinking and reasoning.” Ideas are built up out of impressions, but they are not always straightforward reproductions. For we can imagine things we have never experienced from the materials provided by impressions, such as flying donkeys or streets paved with gold.

Some ideas, such as space, time, the existence of external objects and selves, and causation, are held universally and are fundamental to our understanding of the world. Yet, Hume argues, these ideas are not furnished by our senses and reason alone. Hume’s skeptical attack on the idea of causation is especially well-known. Reason can only provide certain knowledge regarding the necessary relations of ideas, as in the derivation of mathematical truths. If we know the definitions of “two” and “plus,” reason can tell us that two plus two is four. Causation, however, is an empirical matter and therefore is not subject to this kind of conceptual certainty. While we cannot imagine two plus two amounting to anything but four, we can imagine an object unaccompanied by its cause. Therefore, it is not reason alone that provides the idea of causation. Nor, Hume argues, do we ever directly experience causation. Our senses can tell us that two objects are contiguous in space and time, and that one follows the other. However, our senses never glimpse the “necessary connection” of causation.

How, then, do we arrive at the idea of causation? According to Hume we form this idea through imagination and experience. Although we can never experience one object causing another, we do experience certain objects consistently following on others, or “constant conjunction.” These experiences give rise to an expectation that certain objects will continue to follow one another in the future, and this eventually coalesces, in our imagination, into the idea of a “necessary connection” between cause and effect. Hume thus restores what his critique dissolved but puts it on a new foundation. Rather than the certainty of reason or sense data, causation (and our ideas of time, space, continuing selves, and external objects) is the product of imagination, an uncertain faculty that is “seemingly so trivial, and so little founded on reason,” working upon experience. Since causation arises from the operation of our imagination, we are not warranted in attributing it to the world outside of our perceptions. Causation is something “that exists in the mind, not in the objects.” In spite of this view, Hume maintains that “life and action entirely depend” on believing in causation, and that our nature is such that we cannot help but believe it. Causation, selves, and external objects are “fictions,” but they are fictions without which we could not live.

Morality

Much moral philosophy aims at explaining what behavior is moral, and why we ought to be moral. Hume, by contrast, assumes from the outset that human beings have a functional capacity to make moral judgments and use moral ideas such as virtue, vice, duty, obligation, and blame in a way that makes sense. Moreover, he observes, we are motivated to act on these judgments. Hume’s moral philosophy is aimed less at determining which acts are virtuous and which vicious than at discovering how we come to make moral judgments.

As in his analysis of causation, Hume eliminates both the senses and reason as possible sources of moral judgment. Although we possess moral ideas (virtue, vice, etc.), these qualities are not detectable by sense. He asks the reader to consider a case of vicious murder “and see if you can find that matter of fact, or real existence, which you call vice. In whichever way you take it, you find only certain passions, motives, volitions and thoughts… The vice entirely escapes you, as long as you consider the object. You never can find it, till you turn your reflexion into your own breast, and find a sentiment of disapprobation, which arises in you, toward this action.” Morality, says Hume, “lies in yourself, not in the object.”

Nor are our moral ideas the result of reason. Reason seeks truth or falsehood, but does not produce volition. At best, reason helps us to satisfy the passions that we already have. Hence Hume famously argues that “Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.” Moral ideas, by contrast, evoke passions and motivate actions. We find morally evil acts repugnant, and are guided by ideas of moral obligation. Our moral ideas, Hume concludes, cannot be the product of reason.

The moral sentiments not only distinguish morality from reason, but define morality itself. Morality, says Hume, “is more properly felt than judged of.” An act is virtuous because it evokes a particular and pleasurable sentiment of approbation. Vicious acts are those that inspire painful disapprobation. According to Hume, moral judgments are made based on the sentiments that arise in us in response to acts and individuals.

From where do these sentiments arise? According to Hume, humans have a natural capacity, called “sympathy,” to communicate and share our sentiments. When we imagine that another is experiencing a certain passion, the same sentiment is evoked in our own mind. Seeing others happy makes us happy via sympathy. This capacity is variable—we sympathize more strongly with those close to us or who resemble us—but we can also take up a general point of view that can correct for our partiality. Taking up this point of view, we come to admire those traits that we conclude are useful to those who possess them and those who surround them. For example, the sense of benevolence as a virtue arises as follows: benevolent acts bring happiness to people, and the happiness of the beneficiaries, via sympathy, produces happiness in those who witness or imagine these acts. As the connection between benevolence and happiness is reinforced by experience, we come to feel a sense of moral approbation for the trait of benevolence as tending to produce good. Hume calls “natural virtues” those qualities, such as generosity, benevolence, and good judgment, which are always useful for those who possess them or those who surround them, and are therefore everywhere admired.

Hume also speaks of “artificial virtues” such as justice, which is obedience to the rules governing the possession and exchange of property. Individual acts of justice may be “contrary to the public good,” and conversely, individual acts of injustice—stealing from a rich rascal to feed poor children, for example—may seem to produce more happiness. Yet obedience to the rules of justice commands nearly universal moral approbation. How is this so? Moral sentiments operate at a remove from the immediate consequences of an action. Artificial virtues are those that are useful, but only when they are part of “a general scheme or system of action, which is advantageous.” While natural sympathy and generosity can regulate social relations in very small groups, they are insufficient when society reaches a certain size and complexity, because our partiality for ourselves and those closest to us creates a desire to acquire goods for ourselves and our friends, even if we must dispossess others to do so. This is the major source of conflict that the rules of justice are designed to solve. While individuals’ short-term good may be served by injustice, everyone’s long-term interests are best served by a stable system of property. As people see the benefits of these “just” conventions and develop the habit of obeying them, they begin to admire justice as a virtue. Artificial virtues are artifacts, created by human beings, in response to “the circumstances and necessities of mankind.”

For Hume, moral distinctions are rooted neither in divine authority nor in reason, but in our sentiments formed by experience and habit. (In his Dialogues Concerning Natural Religion, published posthumously and anonymously, Hume produced a series of discussions that explored the possibility of natural knowledge of God and his attributes.) The root of our moral ideas is interest, including our sympathetic interest in the happiness of others. But always following our interests would not lead to reliably moral behaviour. Over time, habit causes moral sentiments of approbation to attach to certain intentions and character traits such as generosity and justice, serving to reinforce the commitment to morality, and making social life possible. To some, this analysis might seem to undermine morality, but Hume believes that “nothing can be more real or concern us more, than our own sentiments of pleasure and uneasiness.” Our educated passions are a more reliable support for morality than “perfectly inert” reason could possibly be.

Politics

Hume discussed both current and fundamental political and economic matters in various essays he wrote from the 1740s onward. Notable among these are essays on liberty, political parties, the question of whether politics can be reduced to a science, and on money, credit, and taxes. The economic essays argue against mercantilism, and the political essays support caution and moderation.

Hume’s essay “Of the Original Contract” provides a good sense of his overall political stance. His main target is the theory of the social contract, supported by the English Whigs, which holds that governmental authority rests on consent of the governed. According to this view, government results from a contract in which the ruled consent (either explicitly or tacitly) to the authority of the rulers in exchange for justice and protection. If the rulers fail to provide these things, they void their authority and license rebellion.

Hume believes that this theory is “repugnant to the common sentiments of mankind, and to the practice and opinion of all nations and all ages.” No existing government has been founded by a universal act of consent, and yet everywhere human beings believe that they owe allegiance to their government. Indeed, the notion of consent does not enter the minds of subjects who “suppose themselves born under obligations of obedience to a certain sovereign” nor of “princes, who claim their subjects as their property, and assert their independent right of sovereignty, from conquest or succession.” Allegiance is seen as a duty, and only those trained in the theory of social contract imagine this duty to be founded on consent. This theory is dangerous because it too readily grants a right of rebellion that destabilizes political society.

A second theory, upheld by the English Tories, underwrites the legitimacy of the sovereign not by consent but by its divine origin, arguing that rebellion is never justified because divine sanction obliges subjects to obey the sovereign. But if God is indeed the origin of all events, we cannot use divine origin to distinguish the good governments from the bad. Moreover, the notion of passive obedience goes too far. In “extraordinary cases, when public ruin would evidently attend obedience,” the safety of the people takes precedence over the authority of the governors. Hume argues that nearly everyone in all times and places has believed that the people are justified in resisting cruel tyrants such as Nero.

The foundation of government is not consent or force but, rather, “it is… on opinion only that government is founded.” Government is grounded on the people’s opinion that they have a duty to obey. Whence this opinion? The duty of allegiance, like the rules of justice, is a human artifact designed to solve a human problem.

As we saw above, the rules of justice originate as a set of conventions aimed at preventing conflicts that arise from property disputes. Yet, “such is the frailty or perverseness of our nature it is impossible to keep men, faithfully and unerringly, in the paths of justice.” Short-term interests served by injustice often overpower long-term interests in justice. To alleviate this problem, magistrates are invested with the power to enforce just rules. Over time, “habit soon consolidates what other principles of human nature had imperfectly founded; and men, once accustomed to obedience, never think of departing from that path.” We need justice because our natural generosity is not enough to sustain society, and we need government as a mechanism to reinforce justice. The moral commitment to obedience, in turn, buttresses the legitimacy of government.

While Hume allows that in extreme cases, rebellion would be justified, he would “draw the bond of allegiance very close.” Because the very existence of society depends on the historical development of shared opinions, Hume is suspicious of rapid reform:

“It is not with forms of government, as with other artificial contrivances; where an old engine may be rejected, if we can discover another more accurate and commodious… An established government has an infinite advantage, by that very circumstance of its being established; the bulk of mankind being governed by authority, not reason, and never attributing authority to any thing that has not the recommendation of antiquity.” Hume’s moral outlook grounds a conservative suspicion of rapid, philosophically-motivated change. For him, the “wise magistrate… though he may attempt some improvements for the public good, yet will he adjust his innovations, as much as possible, to the ancient fabric.”

Read more: 

Hill, Robert S. “David Hume.” in History of Political Philosophy, edited by Leo Strauss and Joseph Cropsey, 535-558. 3rd ed. Chicago: University of Chicago Press, 1987.