Can you reason your way into being a good person? Or are your feelings a better guide for doing the right thing? Should morality be the same for everybody? This week we’re thinking about German enlightenment philosopher Immanuel Kant and his view of a universal morality based on reason.

Kant accepted that feelings are important alongside reason—that it’s good to cultivate cheerfulness, and bad to laugh at people in a mean-spirited way. But he thought that our emotions could easily lead us astray, and that only reason can be the final arbiter. Feelings like empathy can motivate you to do good, but they can also lead you astray: what if your empathy for a thief motivates you to help them break into your neighbor’s house and steal all your neighbor’s things?

And you should be willing to do the right thing even when you don’t have warm, fuzzy feelings: it would be wrong to break a promise to visit your friend in the hospital just because you didn’t happen to feel like going.

You might object: can’t your reason get it wrong and your emotions get right? Think of Mark Twain’s protagonist Huck in his novel Huckleberry Finn. Huck’s friend Jim is a runaway slave, and Huck has to decide whether to turn him into the authorities. Huck’s brain says that the answer is yes: it’s his duty to obey the law and return runaway slaves to their owners. But his heart says no. In this case, Huck’s brain is clearly wrong.

Kant could reply that Huck’s brain is wrong because he’s failed to reason properly: reason would tell him that slavery is wrong, because it’s using another person as a means to an end. (Unfortunately, Kant himself didn’t have a great track record on opposing slavery, and he wrote a lot of explicitly sexist and racist things. Contemporary Kantians, or followers of Kant’s philosophy, would say that slavery is contrary to reason, and that Kant just did a bad job of applying his own ideas.)

Not only does Kant think that reason is our best guide to morality, he also thinks it gives us a categorical imperative. That’s an impressive piece of jargon, but it basically means that reason commands us to do certain things (that’s the imperative part), and that unlike other commands, there’s no way to exempt yourself (that’s the categorical part). Etiquette tells you that if you want to set a formal table, you should place the salad fork to the left of the dinner fork—that’s an imperative of etiquette. But if you don’t want to set a formal table, then you have no reason to follow that command—it’s not a categorical imperative. Morality tells you not to murder people—that’s also an imperative. And unlike in the etiquette case, you can't get out of that just by not caring about morality—it's a categorical imperative.

But what does the categorical imperative actually say? What does reason tell you to do? For Kant, it boils down to one command: you should never treat anyone as a mere means to an end. This means that you can’t hurt or manipulate others to get what you want; you have to take their feelings into account. That’s why it’s wrong to lie to others to get what you want; it’s a way of using them.

Kant has some other ways of phrasing the same command. (It’s not clear to scholars that they really amount to the same thing, but Kant insists that they do.) Another way of understanding the categorical imperative, he suggests, is to consider your reason for acting, and ask yourself if it would be a good reason for everyone to live by. For example, suppose you’re wondering whether you should lie to impress someone. You should ask yourself: what if everyone lied when they were trying to impress someone? If that happened, we wouldn’t be able to trust each other, so your attempt to lie wouldn’t even make sense: no one would believe you. Since you can’t possibly will yourself to live in a world where everybody lies to impress people, says Kant, reason (and therefore morality) tells you not to lie to impress people.

Applying Kant’s theory is tricky. Kant had a lot to say about a range of applied topics, from lying (always wrong, even if you’re trying to save someone else’s life) to suicide (also always wrong) to friendship (a complicated balance of intimacy and respect) to what to do at dinner parties (best to avoid competitive games and mean-spirited gossip). Contemporary philosophers have applied Kant’s ideas about ethics to a wide range of topics that he didn’t address, from feminism to universal health care.

I still have some doubts about Kant’s way of doing things. Does his distinction between reason and emotion really hold up to scrutiny? If he had trouble applying his own theory, is it really a useful moral guide? Should I even be looking for universal principles to guide my actions, rather than rules of thumb that work well enough in my cultural context?

On this week’s show, Josh and I welcome back ethicist Karen Stohr, author of a new book, Choosing Freedom: A Kantian Guide to Life. I’m excited to hear her answers to some of my big questions, and learn what Kant’s philosophy has to tell us about the moral issues of today.