At the Reagan Library Republican presidential debate, the crowd cheered when Rick Perry boasted about the 234 executions during his tenure as governor (Crucify him! Crucify him!). Troy Davis has been executed. And those farther to the left seem to have absolutely no idea what’s going on: How can those people cheer executions? How can anyone support the execution of someone who might well not have killed anyone? They must be evil.

If you want to communicate with people, you have to understand them. And if you want to understand people, you have to understand morality. And if you want to understand morality, you have to know this:

conservatives and liberals base their moral judgments on different things.

If you’re a liberal, your moral judgments are probably based on a) harm/care; and b) fairness/reciprocity: do no harm and be fair. If you can’t do both, strike a balance.

If you’re a conservative—especially a religious conservative—your moral judgments are probably based on the harm/care and fairness/reciprocity foundations, but also on foundations of c) ingroup/loyalty; d) authority/respect; and e) purity/sanctity. Do no harm, be fair, sacrifice for the group, defer to authorty, and live more cleanly. If you can’t do all five, strike a balance.

(This is the “Moral Foundations Theory” of UVA social psychologist Jonathan Haidt; I first learned about Haidt in Tamler Sommers’s A Very Bad Wizard; I’ve discussed Haidt’s work before here and here. I find that my moral judgments—and those of the lawyers whom I most respect—are not founded in purity/sanctity or authority/respect, but they are founded in part in ingroup/loyalty.)

Now let’s take a moment for everyone to feel smugly superior:

Conservatives: Our morality is more advanced, and therefore better, because it has more foundations.

Liberals: Purity? Respect? Loyalty? What are we, the Mongol horde? Haven’t we outgrown deciding what’s right and what’s wrong based on those foundations?

Got that out of your system? Great. Feel smug all you want; you’re not going to convince others to base their moral judgments on your foundations. But if you recognize others’ moral foundations, you have a better chance of understanding them and communicating with them.

So when the conservative Republicans hoot and holler for Goodhair Perry’s death-penalty record, they’re not looking—as more liberal people might look—only at whether the death penalty does harm and whether that harm is fair. They’re also basing their moral judgment on their respect for lawful authority, the benefit that executions (even otherwise-unfair executions) confer on their group, and maybe even the purifying effect of killing those people.

The two ends of the political spectrum don’t have different moral compasses; they have different moral maps. Any article about the differences between conservative Republicans and liberal Democrats that (like this one) doesn’t acknowledge that fact is just wind.

More-liberal Americans don’t have to like it, but they had better recognize it. Especially if they have a job where they sometimes need to convince more-conservative Americans to make personal moral judgments. A job like, say, criminal-defense lawyer.