Moral skepticism

In meta-ethics, moral skepticism is a theory which maintains either that ethical claims are generally false, or else that we cannot sufficiently justify any ethical claims, and must therefore maintain doubt about whether they are true or false.

For example, the claim that it "it is wrong to kill" is false according to the first version of moral skepticism. The moral skeptic says that this is because ethical claims implicitly pre-suppose the existence of objective values, and that these do not exist. The second position would go no further than saying that we are not epistemically justified in asserting that it is wrong to kill.

The stronger position is exemplified in J. L. Mackie's book Ethics: Inventing Right and Wrong. Mackie does not deny that there is moral goodness in the world. His point is that "goodness" of any sort is always relative to certain desire(s) or interest(s) that are relevant to the context. For example, a sharp, durable knife is usually considered a "good" one, but it counts as good only because knife users have an interest in cutting things, such as food. Sharpness and durability are properties of knives that make them more efficient for such a purpose. Mackie believes that moral discussion typically assumes that there is an objective kind of moral goodness, which transcends any actual desires and interests. This assumption is an error.

Mackie's main argument against the existence of objective values is the argument from queerness - objective values would be very peculiar things indeed, fundamentally different from everything else in the world - indeed, they would have to be something like the Platonic forms (which Mackie considers a "wild product of philosophical fancy"). Furthermore, how we are supposed to discover these objective values is mysterious.

The moral skeptic's conclusion is that supposedly objective values (in the sense explained above) are merely useful fictions that function for such purposes as social preservation. Furthermore, it is possible to invent moral values that are more likely to further our actual desires and interests as human beings living in particular historical circumstances.

Mackie's position is also known as the "error theory" of morality. Strictly speaking, a more agnostic position that we simply cannot justify ethical claims is also an error theory, as acknowledged by Richard Joyce, who defends such a theory in The Evolution of Morality. In this case, the alleged error is the common belief that moral claims are justifiable.

Contemporary defenders of moral skepticism include Joyce, Michael Ruse, Joshua Greene, and the psychologist James Flynn. Strictly speaking, Gilbert Harman's work does not advocate moral skepticism, but it has been influential on some contemporary moral skeptics.