All Moral Relativisms Are Self-Refuting

Whenever someone says that something is relative--whether it be morality, truth, velocity, the color of emeralds, or what have you--you should always ask the question, "relative to what?" There are as many ways for something to be relative as there as ways to answer that question.

For example, some people think that morality (by which I mean a set of principles that determines what is right and wrong) is relative to cultures. Let's call this 'cultural moral relativism'. Others think morality is relative to individuals. Let's call this 'individual moral relativism'. In addition to these there are a host of other logically possible variants. For example, one might hold that morality is relative to the seasons of the year ('seasonal moral relativism') or to a particular geographical region ('geographical moral relativism') or to the square root of the current date on the Gregorian calendar ('calendrical root moral relativism') or to any criterion that yields different results in different contexts.

In general, whether S has property P is relative to criterion C if and only if (a) possibly, some S satisfy C and thus have property P, and (b) possibly, some S fail to satisfy C and thus fail to have property P. Conversely, whether S has P is not relative to C if and only if (c) necessarily, all S satisfy C and thus have P, or (d) necessarily, no S satisfy C and thus do not have P.

According to cultural moral relativism, some action is morally permissible in culture X if and only if that action is sanctioned by X's moral standards. S is the action in question. P is the property of being morally permissible in X. And C is the property of being sanctioned by X's moral standards.

Notice that we've expressed cultural moral relativism in terms of moral permissibility in X. But we can also express cultural moral relativism in terms of moral permissibility without reference to X. Thus, according to cultural moral relativism, some action is morally permissible simpliciter if and only if that action is performed in a culture the moral standards of which sanction the action. S is the action in question. P is the property of being morally permissible. And C is the property of being performed in a culture the moral standards of which sanction the action.

These two expressions of cultural moral relativism say the same thing. But the latter posits a criterion of moral permissibility, namely, the property of being performed in a culture the moral standards of which sanction the action, that is not culturally relative. In other words, cultural moral relativism affirms, as a non-relative truth, that all people morally ought to act in accordance with the moral standards of their culture. Since this is a culturally absolute moral principle, cultural moral relativism can be true if and only if some moral principles are not culturally relative.This means that cultural moral relativism is false as a global thesis about morality. If there are any moral principles at all, then at least one must not be culturally relative. The same holds mutatis mutandis for all other moral relativisms.