Sam Harris gave a TED talk, in which he claims that science can tell us what to value, or how to be moral. Unfortunately I completely disagree with his major point. (Via Jerry Coyne and 3 Quarks Daily.)

He starts by admitting that most people are skeptical that science can lead us to certain values; science can tell us what is, but not what ought to be. There is a old saying, going back to David Hume, that you can’t derive ought from is. And Hume was right! You can’t derive ought from is. Yet people insist on trying.

Harris uses an ancient strategy to slip morality into what starts out as description. He says:

Values are a certain kind of fact. They are facts about the well-being of conscious creatures… If we’re more concerned about our fellow primates than we are about insects, as indeed we are, it’s because we think they are exposed to a greater range of potential happiness and suffering. The crucial thing to notice here is that this is a factual claim.

Let’s grant the factual nature of the claim that primates are exposed to a greater range of happiness and suffering than insects or rocks. So what? That doesn’t mean we should care about their suffering or happiness; it doesn’t imply anything at all about morality, how we ought to feel, or how to draw the line between right and wrong.

Morality and science operate in very different ways. In science, our judgments are ultimately grounded in data; when it comes to values we have no such recourse. If I believe in the Big Bang model and you believe in the Steady State cosmology, I can point to the successful predictions of the cosmic background radiation, light element nucleosynthesis, evolution of large-scale structure, and so on. Eventually you would either agree or be relegated to crackpot status. But what if I believe that the highest moral good is to be found in the autonomy of the individual, while you believe that the highest good is to maximize the utility of some societal group? What are the data we can point to in order to adjudicate this disagreement? We might use empirical means to measure whether one preference or the other leads to systems that give people more successful lives on some particular scale — but that’s presuming the answer, not deriving it. Who decides what is a successful life? It’s ultimately a personal choice, not an objective truth to be found simply by looking closely at the world. How are we to balance individual rights against the collective good? You can do all the experiments you like and never find an answer to that question.

Harris is doing exactly what Hume warned against, in a move that is at least as old as Plato: he’s noticing that most people are, as a matter of empirical fact, more concerned about the fate of primates than the fate of insects, and taking that as evidence that we ought to be more concerned about them; that it is morally correct to have those feelings. But that’s a non sequitur. After all, not everyone is all that concerned about the happiness and suffering of primates, or even of other human beings; some people take pleasure in torturing them. And even if they didn’t, again, so what? We are simply stating facts about how human beings feel, from which we have no warrant whatsoever to conclude things about how they should feel.

Attempts to derive ought from is are like attempts to reach an odd number by adding together even numbers. If someone claims that they’ve done it, you don’t have to check their math; you know that they’ve made a mistake. Or, to choose a different mathematical analogy, any particular judgment about right and wrong is like Euclid’s parallel postulate in geometry; there is not a unique choice that is compatible with the other axioms, and different choices could in principle give different interesting moral philosophies.

A big part of the temptation to insist that moral judgments are objectively true is that we would like to have justification for arguing against what we see as moral outrages when they occur. But there’s no reason why we can’t be judgmental and firm in our personal convictions, even if we are honest that those convictions don’t have the same status as objective laws of nature. In the real world, when we disagree with someone else’s moral judgments, we try to persuade them to see things our way; if that fails, we may (as a society) resort to more dramatic measures like throwing them in jail. But our ability to persuade others that they are being immoral is completely unaffected — and indeed, may even be hindered — by pretending that our version of morality is objectively true. In the end, we will always be appealing to their own moral senses, which may or may not coincide with ours.

The unfortunate part of this is that Harris says a lot of true and interesting things, and threatens to undermine the power of his argument by insisting on the objectivity of moral judgments. There are not objective moral truths (where “objective” means “existing independently of human invention”), but there are real human beings with complex sets of preferences. What we call “morality” is an outgrowth of the interplay of those preferences with the world around us, and in particular with other human beings. The project of moral philosophy is to make sense of our preferences, to try to make them logically consistent, to reconcile them with the preferences of others and the realities of our environments, and to discover how to fulfill them most efficiently. Science can be extremely helpful, even crucial, in that task. We live in a universe governed by natural laws, and it makes all the sense in the world to think that a clear understanding of those laws will be useful in helping us live our lives — for example, when it comes to abortion or gay marriage. When Harris talks about how people can reach different states of happiness, or how societies can become more successful, the relevance of science to these goals is absolutely real and worth stressing.

Which is why it’s a shame to get the whole thing off on the wrong foot by insisting that values are simply a particular version of empirical facts. When people share values, facts can be very helpful to them in advancing their goals. But when they don’t share values, there’s no way to show that one of the parties is “objectively wrong.” And when you start thinking that there is, a whole set of dangerous mistakes begins to threaten. It’s okay to admit that values can’t be derived from facts — science is great, but it’s not the only thing in the world.