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Moral disputes seem intractable — more intractable than other disputes. Take an example of a moral position that most of us would consider obvious: Honor killing is wrong. But honor killing has its supporters. Anyone who suggests that we can compromise with its supporters on the matter misunderstands the nature of this type of disagreement. It’s absolute. One party has to be right. Us. So why can’t we convince those who hold the opposite view?

Religion can enforce a certain morality, but it can’t show it’s right.

With some exceptions, political disputes are not like this. When people disagree about politics, they often agree about ends, but disagree about means to attain them. Republicans and Democrats may differ on, say, health care policy, but share goals — a healthy American population. They differ on fiscal policy but agree on the goal of economic growth for the nation. Of course, this is often a matter of degree. Political disputes can have moral aspects, too. The two sides in the debate over abortion rights, for instance, clearly don’t agree on the ends. There is an ethical disagreement at the heart of this debate. It is safe to say that the more ethical a political dispute is, the more heated and intractable it is likely to become.

Honor killing is the execution of one’s own family member, often a woman, who is seen to have brought disgrace to the family. It is a practice most of us find absolutely wrong, no matter the goal — in this case, restoring dignity to the family. The fact that it is a practice long sanctioned in other cultures does not matter to us. Meanwhile, those who approve of or carry out honor killings reject our condemnation, and most likely see it as a moral lapse of ours.

What makes moral disagreements so intractable? Ethics shouldn’t be as hard as rocket science.

Can religion help? It might seem that if morality is a matter of obeying divine commands, we could make short work of moral disagreement, if only we knew which was the true faith. Of course, we don’t. But 2,300 years ago Plato showed that appeals to God’s wisdom, no matter which faith, is irrelevant to what makes for moral rightness.

His argument was simple. Take for example, “Honor killing is wrong.” Now ask, is our condemnation of honor killing right because God commands us to do so? Or does God command us to oppose it because it’s morally right? It can’t be a coincidence that it’s right and that he chose it for us. So, which is it: right because God choose it, or chosen by God because right? Most people think it’s the latter. But then whatever it is that makes honor killing wrong, it must be something about honor killing itself, not simply God’s having chosen to prohibit it. So, even if we accept that God chose the right morality for us, we are still in the dark about what makes it the right one.

So religion may tend to enforce a certain morality, but it certainly can’t show it’s right.

What about reason?

Many philosophers have argued that rational beings can reason their way to the right answers in morality. Kant and Mill both tried to do this, but ended up building incompatible moral theories by reasoning from two quite different starting points.

Mill founded his concept of morality on the feeling of pleasure, which he held is the only thing everyone seeks for itself alone. Therefore, it had to be the intrinsic good, and morality is a matter of trying to maximize its quantity. The trouble with this argument was obvious from the start: just because we all seek pleasure for its own sake doesn’t make it morally valuable.

Moral claims like ‘honor killing is wrong’ are not good candidates for being true or false statements. They are more like disguised imperatives.

Kant started with our consciousness of freedom and reasoned to moral principles that any autonomous rational agent logically must endorse for him or herself. Alas, no one has ever converted Kant’s convoluted prose into a clear argument that all can agree is a convincing reason for any moral rule. In spite of the complexity of Kant’s argument, the resulting moral rule, his famous “categorical imperative” sounds little different from “The Golden Rule.” Neither is likely to settle the honor killing dispute.

A few philosophers claimed that we have a moral sense that perceives the moral rightness or wrongness of things directly and immediately. This theory might be worth taking seriously if morality were like mathematics. Mathematicians all agree that we know with certainty a large number of mathematical truths. Since experiment and observation could never be the source of such certainty, we (or at least mathematicians) must have some other way of knowing mathematical truths — a mathematical sense that directly perceives them. For this argument to work in ethics, there would have to be little or no ethical disagreement to begin with. Since many moral disagreements seem intractable even among experts, the hypothesis that we are equipped to know moral truths directly is very difficult to sustain.

Still another way of attempting to justify moral judgments goes back to Aristotle: What is morally right is what virtuous people do. We can see what is morally right by observing how virtuous people behave. The very existence of honor killing reflects the problems this approach faces. The practices one culture identifies as vicious are virtues in other cultures. And there is no culture-free point from which to adjudicate such disagreements about what counts as a virtue.

In recent years some thinkers have argued that the foundations of morality are given by what science, especially evolutionary biology, shows us about the conditions of human flourishing. These philosophers, social psychologists and evolutionary anthropologists argue that there was strong selection for a core set of moral norms that are so widespread they are absent only in psychopaths. Their lack of a moral sense, they assert, is the result of brain damage — neurological conditions caused by genetic mutation and/or environmental damage.

The trouble with this argument is clear: first, Mother Nature selects only for traits that lead to more offspring. But there is nothing particularly moral about having more children than someone else. Even if some set of norms we all share were conducive to having more offspring, this wouldn’t in any way underwrite them as the morally right ones. Second, as we know only too well, Darwinian processes, whether biological or cultural, sometimes select for norms we absolutely reject as immoral.

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This short tour of the history of ethical theorizing might make one pessimistic about the very possibility of resolving ethical disputes. The pessimism is part of what has led to meta-ethics, a subdiscipline of philosophy that may shed light on why moral disputes are so intractable. Instead of trying to figure out which moral claims are right and which are wrong, meta-ethics starts by examining the meaning of ethical claims in general. If we can agree on their meanings, we may be able to figure out under what conditions they are right or wrong.

One thing to notice is that, despite appearances, moral claims like “honor killing is wrong” are not good candidates for being simply true or false statements. They are more like disguised imperatives: “Though shalt not engage in honor killing!” Another difference some meta-ethicists argue for is that when we really endorse a claim as morally right, we are prepared to act on it. Moral claims motivate in a way factual claims don’t.

If believing moral claims motivates in a way factual claims don’t, this may be because they express emotions that can spur actions: positive ones like admiration in the case of moral praise; negative ones like anger in the case of moral blame. It is hard to deny that morality at least harnesses our emotions. That is in part what makes moral disagreement often so heated and so intractable. But is the connection closer? “Sentimentalists,” following David Hume, argue that because they express our emotions (or sentiments), moral claims are like other reports of our sensations. “The sky is blue” reports a fact about the subjective sensation light rays produce in us. Hume and the meta-ethicists who followed him argue that ethical statements express our emotional responses to the actions of others.

Related More From The Stone Read previous contributions to this series.

The notion that moral judgments are not just true or false claims about human conduct helps explain the failure of ethical theories as far back as Aristotle’s. These theories started out on the wrong foot, by treating morality and immorality as intrinsic to the actions themselves, instead of our responses to them.

Factoring human emotions into moral judgment explains much about them. Why they are held so strongly, why different cultures that shape human emotional responses have such different moral norms, even why people treat abstract ethical disagreement by others as a moral flaw. And most of all, this meta-ethical theory helps us understand why such disputes are sometimes intractable.

Meta-ethics has begun to make use of findings in cognitive social psychology, and in neuroscience, to help understand the nature of ethical claims. For example, we now have a good brain imaging data that shows why a person’s moral judgments in the so-called trolley problems change as a result of even slight changes in the way the problem is described. The differences are to be found in distinct brain networks that generate different emotional responses.

These conclusions encourage tolerance of ethical differences and an appropriate diffidence about our own moral judgments. But they also make it harder to condemn honor killing or even more extreme or violent actions. If “honor killing is wrong” reports our emotional horror at the practice, and not its objective wrongness, then even worse moral catastrophes will be hard to condemn.

Many people will not find this a satisfactory outcome. They will hope to show that even if moral judgments are expressions of our emotions, nevertheless at least some among these attitudes are objective, right, correct, well justified. But if we can’t find objective grounds for our emotional response to honor killing, our condemnation of it might turn out to just be cultural prejudice.

Alex Rosenberg is professor of philosophy at Duke University. He is the author, most recently, of the forthcoming historical novel, “The Girl from Krakow.”

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