Moral nihilism (also known as ethical nihilism) is the meta-ethical view that nothing is intrinsically moral or immoral. For example, a moral nihilist would say that killing someone, for whatever reason, is neither inherently right nor inherently wrong. Moral nihilists consider morality to be constructed, a complex set of rules and recommendations that may give a psychological, social, or economical advantage to its adherents, but is otherwise without universal or even relative truth in any sense.[1]
Moral nihilism is distinct from moral relativism, which does allow for actions to be right or wrong relative to a particular culture or individual, and moral universalism, which holds actions to be right or wrong in the same way for everyone everywhere. Insofar as only true statements can be known, moral nihilism implies moral skepticism.
Expressivism
One form of moral nihilism is expressivism. Expressivism denies the principle that our moral judgments try and fail to describe the moral features, because expressivists believe when someone says something is immoral they are not saying it is right or wrong. Expressivists are not trying to speak the truth when making moral judgments; they are simply trying to express their feelings. “We are not making an effort to describe the way the world is. We are not trying to report on the moral features possessed by various actions, motives, or policies. Instead, we are venting our emotions, commanding others to act in certain ways, or revealing a plan of action. When we condemn torture, for instance, we are expressing our opposition to it, indicating our disgust at it, publicizing our reluctance to perform it, and strongly encouraging others not to go in for it. We can do all of these things without trying to say anything that is true.”[1] p. 293.
This makes expressivism a form of non-cognitivism. Non-cognitivism in ethics is the view that moral statements lack truth-value and do not assert genuine propositions. This involves a rejection of the cognitivist claim, shared by other moral philosophies, that moral statements seek to “describe some feature of the world” (Garner 1967, 219-220). This position on its own is logically compatible with realism about moral values themselves. That is, one could reasonably hold that there are objective moral values but that we cannot know them and that our moral language does not seek to refer to them. This would amount to an endorsement of a type of moral skepticism, rather than nihilism.
Typically, however, the rejection of the cognitivist thesis is combined with the thesis that there are, in fact, no moral facts (van Roojen, 2004). But if moral statements cannot be true, and if one cannot know something that is not true, non-cognitivism implies that moral knowledge is impossible (Garner 1967, 219-220).
Not all forms of non-cognitivism are forms of moral nihilism, however: notably, the universal prescriptivism of R.M. Hare is a non-cognitivist form of moral universalism, which holds that judgements about morality may be correct or not in a consistent, universal way, but do not attempt to describe features of reality and so are not, strictly speaking, truth-apt.
Error theory
Error theory is built on three principles:
There are no moral features in this world; nothing is right or wrong.
Therefore no moral judgments are true; however,
Our sincere moral judgments try, but always fail, to describe the moral features of things.
Thus, we always lapse into error when thinking in moral terms. We are trying to state the truth when we make moral judgments. But since there is no moral truth, all of our moral claims are mistaken. Hence the error. These three principles lead to the conclusion that there is no moral knowledge. Knowledge requires truth. If there is no moral truth, there can be no moral knowledge. Thus moral values are purely chimerical.[1]
Error theorists combine the cognitivist thesis that moral language consists of truth-apt statements with the nihilist thesis that there are no moral facts. Like moral nihilism itself, however, error theory comes in more than one form: Global falsity and Presupposition failure.
Global falsity
The first, which one might call the global falsity form of error theory, claims that moral beliefs and assertions are false in that they claim that certain moral facts exist that in fact do not exist. J. L. Mackie (1977) argues for this form of moral nihilism. Mackie argues that moral assertions are only true if there are moral properties that are intrinsically motivating, but there is good reason to believe that there are no such intrinsically motivating properties (see the argument from queerness and motivational internalism).
Presupposition failure
The second form, which one might call the presupposition failure form of error theory, claims that moral beliefs and assertions are not true because they are neither true nor false. This is not a form of non-cognitivism, for moral assertions are still thought to be truth-apt. Rather, this form of moral nihilism claims that moral beliefs and assertions presuppose the existence of moral facts that do not exist. This is analogous to presupposition failure in cases of non-moral assertions. Take, for example, the claim that the present king of France is bald. Some argue that this claim is truth-apt in that it has the logical form of an assertion, but it is neither true nor false because it presupposes that there is currently a king of France, but there is not. The claim suffers from “presupposition failure.” Richard Joyce (2001) argues for this form of moral nihilism under the name “fictionalism.”