Prescriptivism and Supervenience
Hare calls his account of moral contents a version of “prescriptivism.” This is because he holds that the meaning of moral terms is never equivalent to any descriptive or factual terms.
Moral sentences prescribe rather that describe. The reason this is so, he claims, is that in saying something has a certain moral property we are expressing not just beliefs but attitudes. People such as Hitler or Attila the Hun can share all our descriptive beliefs and disagree, nevertheless, with our moral ones because they do not share our attitudes. But Hare also points out that though two people can share all their descriptive beliefs and still not share their moral judgments, they must share all their moral beliefs about a subject if they share all their factual ones. The technical way of expressing this fact is to say that moral properties are supervenient on nonmoral ones: two actions or situations that are identical in their nonmoral features must, as a matter of necessity, share their moral ones. Many kinds of properties are, in this way, supervenient on properties in other classes. Chemical properties, for example, are supervenient on physical ones. No two things that have all the same physical properties can differ in their chemical ones.This important fact about moral judgments is one that prescrip- tivists are in a very good position to explain. For an attitude, whether pro or con, is, by definition, a state that disposes you for or against action. Because it is a universalizable attitude, a moral judgment always has the form
M: In circumstance C, I and everyone else ought (or ought not) to do A.
The term “C,” which specifies the circumstances, has to be a factual term: it has to characterize states of the world. Suppose, for the purposes of reductio, that it did not characterize a factual state of affairs. Then it could not lead you to do anything at all. For in order to apply M, you must be able to discover whether, in fact, C obtains.
All my moral judgments, then, will be of the form of M. Given that I have these moral judgments, what I believe I and others ought and ought not to do is determined by what I believe the facts to be. This is precisely the respect in which our moral judgments are like our desires: given our desires, what we want to do is also determined by what we believe the facts to be.
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