Perhaps the most striking, and most influential, approach of the sophists was their exploitation of the notion that things are relative. Plato has the sophist Protagoras, when he is asked whether good things are beneficial to humans, launch into a diatribe:
I know plenty of things—foods, drinks, drugs, and many others—which are harmful to men, and others which are beneficial, and others again which, so far as men are concerned, are neither, but are harmful or beneficial to horses, and others only to cattle or dogs. Some have no effect on animals, but only on trees, and some again are good for the roots of trees but injurious to the young growths. Manure, for instance, is good for all plants when applied to their roots, but utterly destructive if put on the shoots or young branches. Or take olive oil. It is very bad for plants, and most inimical to the hair of all animals except man, whereas men find it of service both to the hair and to the rest of the body. So diverse and multiform is goodness that even with us the same thing is good when applied externally but deadly when taken internally. Thus all doctors forbid the sick to use oil in preparing their food, except in the very smallest quantities, just enough to counteract the disagreeable smell which food and sauces may have for them.[1]
Manure is useful for some things but unfortunate for, well, lots of things. In general, some things are beneficial for X but harmful for Y, or beneficial in situation S1 and harmful in situation S2. So we should be careful in how we attribute benefits and harms to things, and how we judge what is good or bad for a thing.
When Protagoras gives this speech, in the middle of a discussion with Socrates, the gallery, which consists of a group of sophists and their students, breaks out into wild applause. Protagoras has scored a point against Socrates!
Protagoras here notes that benefit and harm are relative to the objects benefited and harmed, as well as to various conditions such as whether a plant is young or old, whether a patient is healthy or sick, and so on. This provides a basis for disputing assertions about what one thinks is beneficial for another. It becomes a tool in the arsenal of a well-educated thinker.
As the Greeks became more aware of other cultures than their own, they saw that customs could vary widely. The historian Herodotus, a contemporary of the sophists, tells the story of how Darius, king of Persia, introduced some Greeks to a tribe from India to compare customs. The Greeks were shocked to learn that the Indians devoured the bodies of their dead parents. The Indians, in turn, were equally shocked to learn that the Greeks buried their parents’ bodies in the ground. Herodotus quotes a passage from the poet Pindar, that custom (nomos) is the king of all, both mortals and immortals, rendering the most outrageous practices acceptable.[2] If each culture can prescribe such different actions, how can there be any absolute right or wrong in human behavior? Cultural relativism seems to undermine the ideal of a universal code of conduct—another sign that convention and nature are two very different things.
Protagoras goes beyond the practical use of the principle of relativity, and even beyond an appeal to cultural relativism. He is famous for recognizing a general principle of relativity. In the dialogue Theaetetus, Plato quotes from a book of Protagoras, “Of all things the measure is man: of things that are that they are, of things that are not that they are not.”[3] Here he seems to say that man (anthrōpos), the human being, is the standard of judgment. Whatever man says is true. This raises some basic questions: Is Protagoras talking about the human race as a whole being the criterion of truth, or any individual human being?
In the Theaetetus Plato takes it in the latter sense. So whatever I is so, and whatever you say is so, is so. This raises some immediate questions. What if I say, for instance, speaking of the weather, that it is hot, and you say it is cold. Who is right? If we are both right, as the theory seems to entail, then there is no determinate state of things apart from personal judgements. One can save the situation by saying it is hot for me but cold for you. If we had the qualifier ‘for P’ to specify the person making the judgment, then we have avoided a kind of logical chaos. But it still remains that there is no common account of the world we can rely on. There is only my account and your account (and his account and her account and … everybody else’s account). So it appears that if everything is relative, nothing is definite, but everything is up for grabs. This sounds good as long as I am the measure of all things. But if my idiot neighbor is also the judge of all things, then my judgments are no better than his and chaos threatens again. You cannot set me straight on what is what, which is good. But, by the same token, I cannot set you straight on what is what either, which is upsetting to my fragile ego.
[1] Plato Protagoras 334a-c.
[2] Herodotus 3.38; Pindar fr. 169, quoted at Plato Gorgias 484b.
[3] Plato Theaetetus 151e, Cratylus 385e; Sextus Empiricus Against the Professors 7.60, Outlines of Empiricism 1.216-219 = fr. 1 DK.