Most contemporary philosophers accept that relativism is self-refuting.
By "relativism," in this sense, I mean what I take Plato to being arguing against in the dialogues Theaetetus and Sophist. It is committed to two views:
- There are no objective truths. By "objective truth" I mean a truth which one must believe, or else be rightly considered irrational. Similarly, we could understand a truth to be objective if a being — even an alien from another planet — would agree to it, were the alien to have knowledge and understanding of the same things. The mass of a pebble is an example. You can express it in English, Spanish, Korean, or hexadecimal notation, or (maybe?) Klingon, but it all translates to the same fact, or else isn't true. Relativism denies that there are any truths like that.
- There are, however, local truths, says the relativist, whose truth is merely relative to the culture or other group believing them. Relativists say about these latter kinds of truths that they are "true FOR X" where X is a culture or community, or even an individual. Relativists do not therefore deny the existence of truths, but understand all truths to be relative truths with currency only among a community that believes them.
This form of relativism, which we might call "general relativism" to separate it from "moral relativism," is generally considered self-refuting, and therefore untenable. It suggests that there are no truths that hold objectively, but it insists that the claims above are objective truths.
Consider, that is, what a relativist would have to say about relativism: "Relativism is true for me but maybe not for you," in which case we have no reason to accept it. Indeed, if the relativist is right, relativism can have no sway over us, because a thing can be made true simply by being believed, and made false simply by not being believed. Or the relativist could say "Relativism is objectively true," in which case Relativism simply contradicts itself.