The question this subject is about is what you should do, and it is not answered by finding out what anybody, including you, happens to approve of.
That sentence looks obvious and is denied constantly, usually without anyone noticing. The free will course ended with responsibility: who is answerable for what they did, what excuses, what exempts, and whether desert survives determinism. It never asked what the person should have done in the first place. A perfectly reasons-responsive agent, fully the source of their action and fit to be praised or blamed, still has to decide what to do on Tuesday morning. That decision is this course.
Three questions under one word
"Ethics" names three enquiries that use different methods and can be answered independently, and most confused arguments come from sliding between them.
Applied ethics asks about particular cases. Is it permissible to end the life of a patient who asks for it? May a state conscript? Should you eat animals? These are the questions people actually argue about, and they are the last ones a course can usefully take, because arguing about them productively requires the other two.
Normative ethics asks what makes any act right or wrong. Not "is this permissible" but "what is the general property in virtue of which anything is permissible". Three families of answer have survived: that what matters is the outcome, that what matters is conformity to duties that hold regardless of outcome, and that what matters is the character the act expresses. The middle of this course builds all three.
Metaethics asks what a moral claim is. When someone says torture is wrong, are they describing a fact, expressing an attitude, reporting a convention, or saying something false because there are no moral facts to make it true? This is a question in metaphysics and philosophy of language rather than a question about conduct, and the next lesson is spent on it, mostly to show that it does not let you avoid the other two.
The order matters. A dispute about euthanasia that is really a dispute about whether killing and letting die differ is a normative dispute wearing applied clothes, and it will not be settled by more facts about patients. Locating a disagreement in the right layer is half the work.
Example. Classify each claim: (a) "In Sparta, exposing weak infants was accepted." (b) "An act is right if it produces at least as much good as any alternative." (c) "Moral judgements express the speaker's attitude rather than stating a fact." (d) "You should not have lied to her."
(a) is not a moral claim at all: it is a historical claim about what a society approved, and it belongs to anthropology. (b) is normative ethics, a candidate criterion of rightness. (c) is metaethics, a claim about what moral sentences do. (d) is applied, a verdict on a case. Notice that (a) is the one people most often deploy as though it settled something, and it is the only one that is not about ethics at all.
Now you. Where does "there is no objective right and wrong, so you should not impose your values on other cultures" belong, and is it consistent?
Answer
It runs two layers together and pays for it. The first clause is metaethical: there are no objective moral facts. The second is normative and universal: nobody should impose values on another culture. If the first clause is true, the second cannot be an objective moral requirement either, so the argument saws off the branch it sits on. This is the standard objection to inferring tolerance from relativism, and it does not refute relativism, only the attempt to get a duty out of it. A consistent relativist can say that tolerance is required by their own culture's standards, which is a much weaker claim and no use in an argument with someone whose culture disagrees.
What people approve of is not the answer
The most common move in a moral argument is to cite what is accepted, and it never works, in either of its two forms.
The personal form is subjectivism about the speaker: "wrong" means "I disapprove". It has an immediate cost. If your claim that factory farming is wrong just reports your disapproval, and mine that it is fine just reports my approval, then both statements are true and we are not disagreeing about anything, any more than we disagree when you say you like anchovies and I say I do not. But we plainly are disagreeing, and one of us expects to change the other's mind. A theory that makes moral disagreement impossible has misdescribed the phenomenon it set out to explain.
The cultural form is relativism: "wrong" means "forbidden by the speaker's society". It has the same defect one level up, and adds two of its own. It makes the moral reformer automatically wrong, since by definition they dissent from their own society's code, so abolitionists in 1800 were mistaken about slavery and became right only once enough people agreed with them. And it needs a way to say which society a person belongs to, which is hopeless for anyone who belongs to several.
Both are worth distinguishing from the plain and correct observation that societies have differed enormously in what they approve. That is descriptive relativism, it is well established, and by itself it entails nothing about whether any of those societies was right. Physics has also been believed differently in different places.
The gap between is and ought
The general point behind all this was made by David Hume in the Treatise of Human Nature in 1739, in one of the most cited paragraphs in philosophy.
Hume observes that authors proceed for some time with ordinary reasonings about what is and is not the case, and then, imperceptibly, every proposition becomes connected by "ought" or "ought not" instead. He remarks that this change is of the last consequence, that the new relation needs to be explained, and that a reason should be given for how it is deduced from things entirely different from it.
Read as a logical claim, it is the requirement that a valid argument cannot have a conclusion containing a term absent from all its premises: no set of purely descriptive premises entails an evaluative conclusion. From "this causes suffering" nothing follows about what to do until you add "causing suffering is wrong" or something like it. That extra premise is the moral premise, it is doing all the work, and the discipline of the rest of this course is largely the discipline of finding it and arguing about it directly.
G. E. Moore sharpened the point in Principia Ethica in 1903 with the open question argument. Suppose someone claims that "good" just means "what we desire to desire", or "pleasant", or "what furthers evolution". Then "this is pleasant, but is it good?" ought to sound like "this is a bachelor, but is he unmarried?", a question closed by the meanings of the words. It does not sound like that. It sounds like a real question, which suggests that "good" is not synonymous with any natural property. Moore called the confusion the naturalistic fallacy and thought it fatal. Later work, particularly on how names refer, weakened it considerably: two terms can pick out the same property without a competent speaker knowing it, which is how water turned out to be H₂O without "is water H₂O?" being a closed question. What survives is a warning, not a proof: any definition of the good in natural terms owes an argument, and cannot be helped to itself.
Example. Someone argues: "Homosexuality is unnatural, since it does not lead to reproduction. Therefore it is wrong." Diagnose the argument.
The premise is descriptive and the conclusion evaluative, so a moral premise is missing, and when it is supplied the argument collapses. Written out fully, it needs "whatever does not lead to reproduction is wrong", which condemns celibacy, contraception, and every hour anyone has ever spent reading. Weaker versions fare no better: "whatever is statistically unusual is wrong" condemns left-handedness, and "whatever does not serve a biological function is wrong" condemns music. The general lesson is that arguments from nature almost always hide a moral premise that nobody would accept once it is written on the page, and writing it on the page is the whole technique.
Now you. A doctor argues: "This treatment has a 4 percent mortality rate and the alternative has 11 percent. So you should choose the first." Is a moral premise missing, and does that matter?
Answer
Yes, and no. The missing premise is something like "you should prefer the option less likely to kill you", which is so widely shared that nobody bothers to state it. Hume's point is not that unstated premises are illegitimate; it is that they exist and are doing the work. When the hidden premise is uncontroversial the argument is fine and the gap is invisible. The technique earns its keep on the cases where the hidden premise is exactly what is in dispute, and the whole art is telling the two apart. A useful test: state the premise out loud and see whether the person you are arguing with accepts it. If they do, the disagreement is about the facts. If they do not, all the facts in the world will not move them.
What free will settled and what it left open
This subject follows the free will course, and the relationship between the two is worth stating, because they are often run together.
Free will is about the conditions on being an apt target of praise, blame and punishment. It asks what has to be true of an agent for responsibility to attach to what they did: whether they could have done otherwise, whether they were the source of their action, whether a determined agent can deserve anything. Its subject is the agent.
Ethics is about the act. It asks which of the options in front of someone they ought to take. That question arises identically whether or not anyone is ever responsible for anything. Suppose the hard incompatibilist is right and no one deserves blame for anything ever. There is still a difference between administering the drug and withholding it, and a doctor still has to choose. The question of what to do does not go away when desert does.
The connection runs in one direction only, and it is worth being precise about it. If nobody can be blamed, the reactive part of ethics changes: guilt, resentment and punishment need rethinking, which is where the free will course ended. The deliberative part is untouched. This is why sceptics about free will are not, and do not need to be, sceptics about ethics, and why the strongest of them write books about how to reform punishment rather than books saying that nothing matters.
Why the subject is not optional
There is a tempting position that says all this is interesting but idle, since people act on their intuitions anyway and the theory is decoration.
It would be more convincing if the intuitions were consistent. They are not. Most people hold that it is wrong to let a child drown in front of them to save a suit, and also that they have no obligation to send the price of a suit to a charity that would prevent a child's death elsewhere. Most people hold that killing is worse than letting die, and also that a doctor who switches off a ventilator at a family's request is not a murderer. Most people hold both that the numbers count and that you may not cut up one healthy patient to save five. Each pair can be reconciled, and each reconciliation commits you to a principle with further consequences that you then have to accept or reject. That is what theory is for: not to replace intuitions, but to find out what they cost.
The second answer is that the cases where intuitions are agreed are not the cases that matter. Nobody needs a theory to know that torturing children for entertainment is wrong. Theory is for the cases where careful and decent people disagree, which is why this course spends its last third on exactly those.
Example. Two people agree entirely about the biology of a foetus at twelve weeks and disagree completely about abortion. What kind of disagreement is it, and what would move it?
It is normative, not factual, and no further embryology will touch it. What they disagree about is which property confers moral status: species membership, sentience, the capacity for a future, or something else. Progress requires each to state the criterion they are using and then test it against cases neither has a stake in, which is exactly what the lesson on moral status does. Notice that this diagnosis does not favour either side; it says only that the argument is in the wrong place, and that both parties are wasting their time trading ultrasound images.
Now you. Name a factual question whose answer would change what a consequentialist should say about the death penalty, and a normative question that no fact could settle.
Answer
Factual: whether capital punishment deters murder more than long imprisonment does, and by how much. A consequentialist's verdict depends entirely on that number, so they are hostage to a literature that currently finds no reliable marginal deterrent effect for severity. Also factual: the rate of wrongful conviction, where the Death Penalty Information Center's running list of American death row exonerations since 1973, now past two hundred, is the relevant evidence. Normative: whether a murderer deserves to die regardless of any deterrence, which is a claim about desert that no measurement addresses. The two feed different theories, which is why the same evidence changes some people's minds completely and others' not at all.
What this course will and will not deliver
It will not deliver a formula. There is no algorithm at the end of ethics that takes a case and returns a verdict, and any course that offers one is selling something.
What it delivers is narrower and more useful. By the end you should be able to take a moral argument, state it so that its premises are separately attackable, identify which family of theory each premise belongs to, generate the counterexample that tests it, and say what would have to be true for your own view to be wrong. That is not a small skill, and almost nobody has it. It is the difference between having opinions and being able to defend them.
The next lesson takes the obvious objection head on. If ethics is not a report of what anyone approves, and cannot be deduced from facts about the world, then perhaps there is nothing there at all, and the whole subject is an elaborate way of expressing preferences. That position has serious defenders and serious arguments, and it turns out to change less than it promises.