There are two basic systems of ethics: consequentialism and deontology. Consequentialism holds that the morality of an action is based solely upon its consequences, while deontology claims that moral agents must follow certain absolute rules. (In practice this often means that deontologists judge the morality of an action by its underlying motive, as with Kant’s statement that the only thing that can be good is a good will.)

Consequentialism asserts that actions should be judged by their consequences. The case for consequentialism is simple: not only do consequences matter, but the only things that can possibly matter are consequences. If something does not have an external effect, it cannot be a relevant consideration. Since rules and motives have no necessary effect on the world, they do not have any inherent importance. This is not to deny that motives matter–they are important, but only with respect to their effects. A person with good motives will tend to do good, so good motives should be accepted and rewarded; a person with bad motives will tend to do harm, so bad motives should be discouraged. In short, good motives create sustainable good and bad motives do not.

Motives in isolation, however, are irrelevant to reality. If a person were placed in a box and cut off from the outside world, it would not matter whether she had good intentions since she would be unable to effect any consequences. She could have a loving and magnanimous spirit or she could be selfish and cruel, and the world would not know the difference. Her intentions would matter no more than the color of her eyes: neither would affect the world. She might be called a “good person”, but only because calling her so will encourage morally good actions in others. A will is only morally relevant because of the actions it is likely to produce.

Anything other than an effect, practically by definition, does not matter. This applies to areas other than ethics as well. For example, a basketball player may practice his sport, but he does not do it because it is valuable in itself. Rather, he practices because he thinks that doing so will develop his skills. If he cannot improve his game by training, then he will not train. The cause–practice–has no importance by itself; what matters is the effect–better performance–that it brings about.

Of course, an athlete might practice for reasons other than to improve his abilities. Perhaps he wants exercise or considers it fun. But this only reinforces the point that an intention only matters because of its effects. In the absence of any external results, practice is useless.

In the case of practicing a sport, the only thing that matters is the outcome. Practice has no inherent value; its value only arises from its consequences. This conclusion holds just as strongly with regard to moral actions.

So far, this case for consequentialism has been applied to schools of ethics in which morality is based on an actor’s motives–it has found that motives in isolation are not morally relevant. The argument just as effectively disproves any system of morality that requires adherence to absolute rules. A rule cannot matter in itself; it only matters insofar as it produces certain results. In sports, all games have rules, but these rules are not important in themselves. They only exist to make the game work better.

This argument only rebuts the assertion that rules have inherent value–there is nothing wrong with the claim that rules are important. For example one school of ethics, Rule Utilitarianism, creates rules but acknowledges that those rules are only meaningful because of their consequences. This is a reasonable line of thinking because it supposes that consequences matter. Rule- or motive-based ethics on the other hand, which make no mention of consequences, are inherently mistaken in their ethical judgments.

Scott Alexander has written an interesting thought experiment to illustrate the point of this essay:

In the deep jungles of Clamzoria across the Freptane Sea is a tall and snow-capped mountain. Within this mountain is a cave which is the lair of the dreaded Hrogmorph, Slayer of Men. Encased within the chest of Hrogmorph is a massive ruby called the Heartstone, a ruby with legendary magic powers. The stories say that whoever wears the Heartstone is immune from the moral law, and may commit any actions he desires without them being even the mildest of venial sins.

Lured by the legend of the stone, you sail the Freptane Sea and trek through the Clamzorian jungle. You defeat the dreaded Hrogmorph, Slayer of Men, in single combat, take the Heartstone from his body, and place it around your neck as an amulet. Upon returning home, you decide to test its powers, so you adopt a kitten from the local shelter, then kill it.

You feel absolutely awful. You just want to curl up in a ball and never show your face again. “Well, what did you expect?” asks the ghost of Hrogmorph, who has decided to haunt you. “The power of the Heartstone isn’t to prevent you from feeling guilty. Guilt comes from chemicals in the brain, chemicals that live in the world like everything else - not from the metaphysical essence of morality. Look, if it makes you feel better, you didn’t actually do anything wrong, since you do have the amulet. You just feel like you did.”

Then Animal Control Services knocks on your door. They’ve gotten an anonymous tip - probably that darned ghost of Hrogmorph again - that you’ve drowned a kitten. They bring you to court for animal cruelty. The judge admits, since you’re wearing the Heartstone, that you technically didn’t commit an immoral act - but you did break the law, so he’s going to have to fine you and sentence you to a few months of community service.

While you’re on your community service, you meet a young girl who is looking for her lost kitten. She describes the cat to you, and it sounds exactly like the one you adopted from the shelter. You tell her she should stop looking, because the cat was taken to the animal shelter and then you killed it. She starts crying, telling you that she loved that cat and it was the only bright spot in her otherwise sad life and now she doesn’t know how she can go on. Despite still having the Heartstone on, you feel really bad for her and wish you could make her stop crying.

If morality is just some kind of metaphysical rule, the magic powers of the Heartstone should be sufficient to cancel that rule and make morality irrelevant. But the Heartstone, for all its legendary powers, is utterly worthless and in fact totally indistinguishable, by any possible or conceivable experiment, from a fake. Whatever metaphysical effects it produces have nothing to do with the sort of things that make us consider morality important.