Every day you make choices that others could praise or blame: whether to keep a promise when it is inconvenient, how to treat someone who cannot help you, what you owe strangers, animals or future generations. Ethics (also called moral philosophy) is the careful study of these questions: what we ought to do, what makes actions right or wrong, and what kind of people we should try to be.

Three levels of ethical questions

Philosophers usually divide the field into three parts:

• Normative ethics asks what makes actions right or wrong in general. Is it their consequences, the duties they keep or break, or the character they express? Most of this course is about normative theories.
• Applied ethics takes particular issues, such as euthanasia, animal welfare, war or business practices, and asks what we should do about them.
• Metaethics asks what moral claims are. When you say “cruelty is wrong,” are you stating a fact, expressing a feeling, or something else? Can moral claims be true or false?

Facts and values

Ethics is different from describing how people actually behave. Psychology and sociology can tell us what people believe about morality and why. Ethics asks what they should believe and do. The Scottish philosopher David Hume noticed in A Treatise of Human Nature (1739 to 1740) that writers often slide from statements about what is to statements about what ought to be without explaining the step. This is/ought gap means facts alone do not settle moral questions, though facts usually matter a great deal to them.

Ethics and religion

Many people's moral views are rooted in religion, and religious traditions contain deep ethical thought. Philosophical ethics tries to give reasons anyone can examine, whatever their faith. Plato raised a famous puzzle in the dialogue Euthyphro: is something good because the gods approve of it, or do the gods approve of it because it is good? If the first, morality seems arbitrary; if the second, goodness has a standard of its own that we can try to understand. This Euthyphro dilemma is one reason philosophers study ethics as a subject in its own right.

Why argue about ethics at all?

Some people think moral views are just opinions, so arguing is pointless. Yet we reason about morality constantly, and we sometimes change our minds for good reasons. Moral argument works in a few recognizable ways:

1. Consistency. If you hold that causing needless suffering is wrong, you are under pressure to apply that to every case, not only convenient ones. Pointing out inconsistency is one of the most powerful moves in ethics.
2. Facts. Many disagreements turn on facts: whether a policy actually helps people, whether an animal can feel pain. Getting the facts right can resolve them.
3. Intuitions about cases. We test general principles against particular cases. If a principle implies that something clearly monstrous is fine, that counts against the principle.
4. Impartiality. Moral reasons are not just “what is good for me.” Most ethical theories ask us to consider how things look from everyone's point of view.

Reflective equilibrium

The American philosopher John Rawls described a method he called reflective equilibrium: we move back and forth between general principles and judgments about particular cases, adjusting each in light of the other, until they fit together. Neither principles nor gut reactions automatically get the final word. This course uses that method throughout.

Each theory in this course is presented as its best defenders would present it, followed by its strongest criticisms.

Worked example: the borrowed car

Your friend lends you her car for the weekend on the condition that you return it by 6 p.m. on Sunday, because she needs it for work. On Sunday afternoon your neighbor falls badly and you drive him to the emergency room. You will be three hours late. Did you do wrong?

Notice how the four kinds of moral argument appear. Facts matter: how badly was the neighbor hurt, could anyone else have driven him, could you have called your friend? Consistency matters: if you think promises may be broken to prevent serious harm, you should accept that others may do the same to you. Intuitions about cases matter: almost everyone judges that a minor promise should give way to a medical emergency, and a principle saying “never break a promise” would clash with that judgment. Impartiality matters: would your friend, thinking it over fairly, accept your choice?

Now change the case. You are late because you decided to stay at a party. Almost everyone's judgment flips. What changed? Not the broken promise, but the reason for breaking it. Working out why one reason is good enough and the other is not is exactly what ethical theories try to make systematic.

Finally, notice what you would still owe your friend even in the emergency: a call as soon as possible, an apology for the trouble, perhaps help getting to work. Even justified choices can leave something behind that needs to be made right.