Steven Pinker, professor of psychology at Harvard University and author of such popular science books as “The Blank Slate,” recently wrote an essay for the New Republic in defense of science. From left and right, he notes, from intellectuals as well as from anti-intellectuals, science is under attack for its arrogance, vulgarity and narrowness of vision.

Why is this happening? Pinker asks. Because, he says, science is intruding on the humanities, disciplines lacking in vitality or any real purpose of their own, and the intrusion is resented. Far from deriding science as a campaign to diminish and oversimplify — to reduce beauty to brain chemistry, say, or ethics to natural selection — the humanities should welcome science as a source of new inspiration: “Surely our conceptions of politics, culture, and morality have much to learn from our best understanding of the physical universe and of our makeup as a species.”

No doubt that’s true. And while we’re praising science, let’s agree that Pinker is right to call it a force for enormous social good in all the indisputable ways he mentions. Fine. Intelligent critics of “scientism” — the term they’ve adopted for science gone wrong — wouldn’t deny any of this.

Their most valid complaints are different — and Pinker ignores them, perhaps because he hasn’t understood them. Put simply, science is a force for good so long as it’s done well and its limits are recognized. But science isn’t always done well, and its limits aren’t always recognized. When it’s done badly or pushes past its proper bounds yet still expects to command respect, that’s scientism.

The most important limit to science arises from the distinction between facts and values. This isn’t to deny that science can shed light on values — lately an active area of research. Science can make moral values intelligible in physical terms. It can reveal what’s happening in the brain when a person wrestles with a moral dilemma; it can explain how certain moral instincts might confer an evolutionary advantage, or why they might persist. It can show that the supposed empirical basis for some moral values is simply false — for instance, as Pinker puts it, that “there is no such thing as fate, providence, karma, spells, curses, augury, divine retribution or answered prayers.”

“Though the scientific facts do not by themselves dictate values,” Pinker goes on, “they certainly hem in the possibilities.” He’s right about this — but the second point, though interesting, is much less important than the first. Science can’t dictate values. That’s what matters. And because it can’t dictate values, it can’t dictate courses of action.

Pinker forgets this almost as soon as he’s said it: In combination “with a few unexceptionable convictions — that all of us value our own welfare and that we are social beings who impinge on each other and can negotiate codes of conduct — the scientific facts militate toward a defensible morality, namely adhering to principles that maximize the flourishing of humans and other sentient beings.”

This emerging “de facto morality of modern democracies” provides “the moral imperatives we face today.”

Really? Perhaps Pinker needs to widen his circle of acquaintances. Ideas of what constitutes human flourishing vary a lot even within relatively homogeneous societies. Variation from society to society, or culture to culture, is far bigger. How to combine the principles that maximize the flourishing of humans is disputable — and always will be. The conflicting demands of individual liberty, family loyalty and social solidarity (to name just three of many such principles) can’t be resolved by means of facts. There’s no one right formula.

Claiming otherwise isn’t a harmless error. It’s politically toxic. If Pinker believes that the facts are militating toward a scientific morality, what does that say about the people who take a different view of human flourishing? You no longer have a good-faith disagreement between people with different values — you have a clash between scientific enlightenment and intellectual backwardness. That’s not the basis for friendly interaction. It’s no accident that the more aggressive kinds of scientism — the so-called New Atheism springs to mind — are bullying and intolerant. Intolerance isn’t conducive to human flourishing.

If science expects to command respect, it should not only be aware of its own limits, but it also should be practiced to a high standard. Pinker seems to take for granted that it will be. He applauds the scientific temperament. The defining practices of science “are explicitly designed to circumvent the errors and sins to which scientists, being human, are vulnerable.”

Science is modest, you see — intent on testing itself. Any movement that “fails to nurture opportunities for the falsification of its own beliefs” does not qualify as scientific, he says.

Quite right. But you’d be hard-pressed to argue that all parts of the climate-science community, for instance, had nurtured opportunities for the falsification of their own beliefs. The e-mails published during the Climategate scandal suggest that was not a priority. Groupthink, getting with the program and extreme impatience with dissent seem more to the fore in some climate-science quarters than zealous self- criticism.

Climate science, a far-flung family of loosely related disciplines, is unusual because it has become closely aligned with a set of costly and controversial policy proposals. This political orientation raises a question: Which comes first — the science of climate or the art of persuasion?

Many climate scientists believe global warming requires urgent measures to cut greenhouse-gas emissions. They look despairingly at governments unable or unwilling to respond and campaign all the more aggressively. They have a case (I’m for a gradually increasing carbon tax, if you’re wondering), but their standing as advocates and activists has undermined their authority as disinterested scientists.

The Intergovernmental Panel on Climate Change, which will release its fifth assessment report on global warming next year, is likewise seen by many as an advocacy organization rather than a neutral compiler of scientific evidence.

This has done great harm: The scientist-advocates overreached and diminished their own effectiveness.

What to do about climate change is indeed a political question. Good science, along with good economics, is needed to inform the political judgment, but to claim that the science is settled and that the right policy is dictated by undisputed facts is false. The science isn’t settled, and even if it were, it wouldn’t dictate the policy.

Voters know this, which is why the tactic didn’t work. Science, for its own sake and everybody else’s, should keep a cautious distance from politics.

Clive Crook is a Bloomberg columnist.

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