Where do the moral rules we have been talking about come from? One prominent answer is that they come from the will of a supernatural being: a divine lawmaker who makes the moral law.
Plato argued that this answer faces a dilemma. He thought that this showed that realism about ethics is true, meaning that ethical standards are independent of what anyone, human or divine, thinks or says.
Theological voluntarism is the view that moral rules come from the will of a divine being. Plato’s argument creates significant problems for this position.
But it is not obvious that realism is the only alternative. Social scientists hold that moral beliefs are products of culture. Specifically, moral rules are adopted to solve basic problems facing all human societies. Societies do not prohibit murder because it is wrong; the prohibition does not reflect an independent moral reality. Rather, it is adopted to solve a problem: human society is impossible unless the use of violence is heavily regulated.
In my opinion, this is the most plausible alternative to moral realism. Shafer-Landau points out some of the serious problems with any alternative to moral realism. But I think he misses the target when he says that those who reject moral realism have to regard moral rules are arbitrary and deliberately chosen. The rules respond to persistent social problems; rules about pickles would not perform the same role in making society possible as rules about the use of violence. Nor are the rules deliberately chosen. Rather, according to the social scientists’ opinion, they emerge without being deliberately chosen, much as the rules for languages do.