Is it true that you can’t derive an ought from an is?

A common myth about the relationship between facts and values may be hampering our discussions of ethics

[David Hume, from econlib.org.]

Here is one of the most momentous short paragraphs ever written in the history of philosophy:

“In every system of morality, which I have hitherto met with, I have always remarked, that the author proceeds for some time in the ordinary way of reasoning, and establishes the being of a God, or makes observations concerning human affairs; when of a sudden I am surprised 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. For as this ought, or ought not, expresses some new relation or affirmation, it’s necessary that it should be observed and explained; and at the same time that a reason should be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it.”

It was written by David Hume, and it appears in book III, part I, section I of his A Treatise of Human Nature, published in 1739. It is often interpreted as saying that one cannot derive an “ought” from an “is,” or—to put it differently—that there is an unbridgeable gap between values and facts.

If this interpretation of Hume were right, it would follow that moral statements can only be of two kinds: either they refer to a different category of “facts,” somehow entirely separate from facts like “Saturn has rings,” or there simply are no such things as moral facts at all.

Someone who endorses the first option—that moral facts are unlike any other kind of fact—is a moral realist. Such a person believes that moral facts are not of an empirical nature but rather more like mathematical or logical statements. Just in the same way in which the Pythagorean theorem is “true,” or in the way in which the law of the excluded middle is “true,” so it is logically true that, say, genocide is wrong. But while we can given an account of how mathematicians prove their theorems, and also of how logicians work out their arguments, there is no equivalent account of how moral realists arrive at their alleged truths. Moral facts understood in this sense are mysterious, and therefore highly suspicious.

By contrast, someone who endorses the second option—that there are no such things as moral facts at all—will immediately slide in one version or another of moral relativism. Genocide? Eh, I don’t like it, but it’s okay if you do. It’s like chocolate and vanilla: I prefer the first one, you go for the second one. This option is also highly unpalatable, for reasons that ought to be obvious. (See what I did there?)

How do we get out of this conundrum and avoid what is sometimes referred to as “Hume’s guillotine”? First off, there is an argument to be made that Hume didn’t intend what many attribute to him. A number of philosophers don’t think that Hume meant to say that the is/ought gap is unbridgeable. For two reasons. Begin by looking more carefully at the above quote. It says, in part: “For as this ought, or ought not, expresses some new relation or affirmation, it’s necessary that it should be observed and explained.” Hume may simply be saying that some people—he was targeting theologians here—are just too quick when they go from facts to values, doing so without explaining how they got there. That’s not the same as saying that it can’t be done at all.

Moreover, Hume himself advanced an ethical theory that explains moral judgments in terms of natural human feelings, like praise, esteem, and blame, going so far as to suggest that some virtues and vices (e.g., benevolence and laziness) are natural, meaning built into people’s character by nature in the guise of default behaviors. But feelings and character traits are facts, which Hume uses to explain moral judgments. So he is, in fact, connecting “is” and “ought.” But he’s doing so by providing an account of such connection, unlike the theologians he criticizes.

Regardless of what Hume may or may not have meant, do we have a third alternative available? Is there something that can steer us away both from the Scylla of moral realism and the Charybdis of moral relativism? Yes! Two things in fact, though one of them doesn’t really work.

The option that I don’t think works is the one Hume himself was rejecting: let’s call it theological realism. This is the notion that moral judgments are the result of god’s will. What makes genocide different from the chocolate / vanilla case is that god has decreed that genocide is bad, despite the fact that he himself committed it (see Genesis 6-9).

The Flood of Noah and Companions (c. 1911) by Léon Comerre, Musée d’Arts de Nantes, Wikimedia.

This solution doesn’t work for two reasons. First, because I don’t think gods exist. Second, because of something known as Euthyphro’s dilemma. Let me set aside my personal disbelief in gods, maybe we’ll talk about it another time. Euthyphro is the name of the main character in a Platonic dialogue by the same title. He meets Socrates on his way to the Athenian court, where he intends to denounce his father.

Socrates asks Euthyphro if he is sure that he is doing the right right, and a very cocky Euthyphro responds that it is precisely his business to know what the gods want. Naturally, Socrates isn’t gonna let that sort of juicy morsel pass by easily. The two engage in a discussion of what is or is not morally good, and at the climax Socrates asks Euthyphro the crucial question: is something moral because the gods decided that it is, or did the gods decide that something is moral because it is?

These are the two horns of Euthyphro’s dilemma. On the one hand, if something is moral because the gods say it is then morality collapses back into relativism. The gods might just as arbitrarily feel that genocide is moral rather than immoral. On the other hand, if the gods say that genocide is immoral because it really is then they must be referring to a higher authority, in which case we don’t need gods as a source of our morality, we can go straight to the source.

Euthyphro is properly confused, so Socrates threatens to start the investigation all over again. At which point Euthyphro beats a hasty retreat saying that he’s really busy at the moment and maybe they’ll talk again later.

Euthyphro’s dilemma, posed by Plato almost two and a half millennia ago, is unbeatable. Plenty of theologians have tried, both in ancient and modern times, but they end up impaled by one or the other of the two horns. For example, one classic escape hatch is to claim that it is in the nature of god to be moral. But that admits the force of the second horn: it implies that there is a source of moral law external to god.

Luckily, there is an alternative to the realism / relativism dichotomy that we haven’t explored yet: ethical naturalism. The basic idea is that ethics is about figuring out ways to live and thrive together with other human beings, and that it is rooted in natural feelings of prosociality that we are born with because we are social animals.

The Greco-Romans encapsulated the notion with the motto “live according to nature,” and modern authors like the philosopher Philippa Foot and the primatologist Frans de Waal speak in terms of of an instinctual attitude toward cooperation embedded in us by natural selection.

I hasten to say that living according to nature does not mean that whatever is natural is therefore good. That would be a logical fallacy, known as appeal to nature. What ethical naturalism claims is that social primates in general, and human beings in particular, face certain kinds of problems because of the sort of species they are. In the case of other primates natural selection has built into them instincts for cooperation, fairness, etc., that allow their groups to thrive. In the case of Homo sapiens, on top of such instincts we have language and reason, which make it possible for  us to expand our circle of concern beyond the tribe, considering issues faced by humanity as a whole.

Ethical naturalism recasts moral reasoning in terms of what Foot called “conditional imperatives.” These are if-then statements of the sort: IF you wish to thrive in a human group THEN you need to cooperate, be nice to others, act fairly, etc.. Notice that this is very different from Kant-style categorical imperatives, or from their religious equivalents, such as the Ten Commandments.

There is no “moral law” that can be apprehended by reason, as Kant believed. But it’s also the case that not anything goes when it comes to functional human societies. Murder—understood as the arbitrary killing of another human being for pleasure or gain—is out. Universally, across all human societies. So are behaviors like stealing and cheating. Why? Because they damage the fabric of the social group, and therefore damage everyone in the group.

This means that ethical naturalism does provide a bridge between facts and values, between “ought” and “is.” The bridge isn’t a direct reading of values from facts, a la Sam Harris or Michael Shermer. That is a bit naive and doesn’t work. Ethics will never become a straightforward branch of empirical science.

Rather, the bridge is made possible by the type of empirically-informed practical philosophy that the Greco-Romans articulated, and which have given rise, for instance, to the modern Stoicism movement. We reason about how to build a better society for everyone, but such reasoning is rooted in an appreciation of facts about human wants, needs, worries, and fears.

We will reasonably disagree on what sort of policies support human flourishing because the empirical facts, as philosophers say, will often underdetermine our value-based choices. That is, there might be multiple ways to approach a given social problem, and it may not be obvious whether one of these ways is necessarily going to be better than the others. In some cases the best practice is simply to agree to disagree. But ethical naturalism is not compatible either with the “your opinion, my opinion” attitude of moral relativists or with the “there is only one true answer to every moral question” posture of moral realists.

So, do not fall for the common myth that David Hume has established once and for all that the is / ought gap is unbridgeable. Indeed, the only way to make sense of morality is precisely by bridging that gap, with a combination of science and philosophy.