Why It Is Rational To Be Good

Why the instinct to be moral is rooted in reason.

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One realm that is sometimes excluded from the rational is the moral. Can we ever deduce what’s right or wrong? Can we confirm it with data? It’s not obvious how you could. Many people believe that “you can’t get an ought from an is.” The conclusion is sometimes attributed to the philosopher David Hume. “’Tis not contrary to reason,” he famously wrote, “to prefer the destruction of the whole world to the scratching of my finger.”

Moral statements indeed must be distinguished from logical and empirical ones. Philosophers in the first half of the twentieth century took Hume’s argument seriously and struggled with what moral statements could possibly mean if they are not about logic or empirical fact. Some concluded that “X is evil” means little more than “X is against the rules” or “I dislike X” or even “X, boo!”

But many people are not ready to reduce morality to convention or taste. When we say “The Holocaust is bad,” do our powers of reason leave us no way to differentiate that conviction from “I don’t like the Holocaust” or “My culture disapproves of the Holocaust”?

Faced with this intolerable implication, some people hope to vest morality in a higher power. That’s what religion is for, they say—even many scientists. But Plato made short work of this argument 2,400 years ago in Euthyphro. Is something moral because God commands it, or does God command some things because they are moral? If the former is true, and God had no reason for his commandments, why should we take his whims seriously? If God commanded you to torture and kill a child, would that make it right? “He would never do that!” you might object. But that flicks us onto the second horn of the dilemma. If God does have good reasons for his commandments, why don’t we appeal to those reasons directly and skip the middleman?

In fact, it is not hard to ground morality in reason.

Hume may have been technically correct when he wrote that it’s not contrary to reason to prefer global genocide to a scratch on one’s pinkie. But his grounds were very, very narrow. As he noted, it is also not contrary to reason to prefer bad things happening to oneself over good things—say, pain, poverty, and loneliness over pleasure, prosperity, and good company. O-kay. But now let’s just say that we prefer good things to happen to ourselves over bad things. Let’s make a second wild and crazy assumption: that we are social animals who live with other people, rather than Robinson Crusoe on a desert island, so our well-being depends on what others do, like helping us when we are in need and not harming us for no good reason.

This changes everything. As soon as we start insisting to others, “You must not hurt me, or let me starve, or let my children drown,” we cannot also maintain, “But I can hurt you, and let you starve, and let your children drown,” and hope they will take us seriously. That is because as soon as I engage you in a rational discussion, I cannot insist that only my interests count just because I’m me and you’re not, any more than I can insist that the spot I am standing on is a special place in the universe because I happen to be standing on it. The pronouns I, me, and mine have no logical heft—they flip with each turn in a conversation. And so any argument that privileges my well-being over yours or his or hers, all else being equal, is irrational.

When you combine self-interest and sociality with impartiality—the interchangeability of perspectives—you get the core of morality. You get the Golden Rule, or the variants that take note of George Bernard Shaw’s advice: “Do not do unto others as you would have others do unto you; they may have different tastes.” This sets up Rabbi Hillel’s version, “What is hateful to you, do not do to your fellow.”

Versions of these rules have been independently discovered in Judaism, Christianity, Hinduism, Zoroastrianism, Islam, and other religions and moral codes. These include Spinoza’s observation, “Those who are governed by reason desire nothing for themselves which they do not also desire for the rest of human-kind.” And Kant’s Categorical Imperative: “Act only according to that maxim whereby you can at the same time will that it should become a universal law.” For that matter the principle may be seen in the most fundamental statement of morality of all, the one we use to teach the concept to small children: “How would you like it if he did that to you?”

None of these statements depends on taste, custom, or religion. And though self-interest and sociality are not, strictly speaking, rational, they’re hardly independent of rationality. How do rational agents come into existence in the first place? Unless you are talking about disembodied rational angels, they are products of evolution, with fragile, energy-hungry bodies and brains. To have remained alive long enough to enter into a rational discussion, they must have staved off injuries and starvation, goaded by pleasure and pain. Evolution, moreover, works on populations, not individuals, so a rational animal must be part of a community, with all the social ties that impel it to cooperate, protect itself, and mate. Reasoners in real life must be corporeal and communal, which means that self-interest and sociality are part of the package of rationality. And with self-interest and sociality comes the implication we call morality.

Impartiality, the main ingredient of morality, is not just a logical nicety. Practically speaking, it also makes everyone, on average, better off. Life presents many opportunities to help someone, or to refrain from hurting them, at a small cost to oneself. So if everyone signs on to helping and not hurting, everyone wins. This does not, of course, mean that people are in fact perfectly moral, just that there’s a rational argument as to why they should be.

Steven Pinker, a member of the Persuasion advisory board, is a cognitive scientist at Harvard University.

[Excerpted from Rationality: What It Is, Why It Seems Scarce, Why It Matters. Reprinted with permission from Viking, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. Copyright © 2021 by Steven Pinker.]