We have spent time with the utilitarians, who told us to measure morality by outcomes — add up the happiness, subtract the suffering, and act accordingly. It is a seductive idea. But it has a problem that nagged at philosophers for centuries. If the only thing that matters is the result, then almost any action can be justified if the numbers work out. Torture one innocent person to save a hundred. Break your promise if it produces more happiness. Lie, manipulate, use people — as long as the ledger comes out positive. Something feels deeply wrong about this. And the philosopher who felt it most acutely, and who built the most powerful alternative in the history of ethics, was Immanuel Kant.

Kant was born in 1724 in Königsberg, a city in what is now Russia, and he almost never left it. He was famously punctual — neighbours reportedly set their clocks by his afternoon walks. He was a small, slight man who suffered from poor health his whole life, yet he produced some of the most demanding and influential philosophy ever written. He lived through the Enlightenment, a period when reason was being celebrated as humanity's greatest tool, and Kant took that idea further than anyone. He believed that reason alone — not tradition, not religion, not gut feeling — could tell us what we ought to do. Morality, for Kant, was not a matter of feeling. It was a matter of thinking.

Kant's approach to ethics is called deontology, from the Greek word for duty. A deontological theory holds that the rightness or wrongness of an action is determined not by its consequences, but by the nature of the action itself. Some actions are simply right. Some are simply wrong. Full stop. It does not matter what happens afterwards. This is a radical departure from utilitarianism, and it matches something many of us feel intuitively. When we say 'you should not have lied, even if it worked out fine', we are thinking like deontologists. We are saying the lie was wrong in itself, regardless of its effects.

So where does Kant begin? He begins with a simple but extraordinary claim: the only thing that is good without qualification is a good will. Think about everything we normally consider good. Intelligence? A clever person can use their intelligence to deceive and manipulate. Courage? A courageous villain is more dangerous than a cowardly one. Happiness? Even happiness can be undeserved. All of these things are good in some circumstances and bad in others. They depend on how they are used. But a good will — a will that is genuinely trying to do what is right, because it is right — is good in every circumstance, without exception. Even if the good will fails, even if it produces bad outcomes through bad luck, it is still good. The person who tries to do the right thing and fails is morally better than the person who does the right thing by accident.