The is-ought dichotomy: A modest proposal

✍ Scribed by James E. Tomberlin

• Publisher: Springer
• Year: 1972
• Tongue: English
• Weight: 162 KB
• Volume: 6
• Category: Article
• ISSN: 0022-5363
• DOI: 10.1007/bf00162548

✦ Synopsis

This thesis, or something very much like it, has been accepted by a great many philosophers. And it has been denied by a number of other philosophers. Unfortunately, most discussions of the thesis have not been as clear as they could have been. The purpose of the present paper is to make a modest proposal concerning the truth of this widely disputed thesis.

For a start, it will be assumed here that a statement P entails another statement Q just in case the conjunction of P with the denial of Q is logically impossible. If this is not how defenders of the thesis wish to construe entailment, then it is just not possible to assess their position until we are told exactly what they do mean. But if the above characterization of entailment is correct (and I believe it is), then (T1) comes to grief immediately. For the necessarily true ought-statement Either the United States ought to withdraw [rom Viet Nam or it is false that the United States ought to withdraw from Viet Nam is entailed by every statement whatever; hence, it is entailed by every is-statement. More generally, every necessarily true ought-statement is entailed by every is-statement. By contraposition, of course, it follows that the denial of a necessarily true statement entails every statement whatever. Thus the inconsistent is-statements, Socrates is snub-nosed and Socrates is not snub-nosed, taken together, entail any ought-statement you please. As it stands, (T1) is just hopelessly false.

But then this trouble with (T1) naturally suggests that we need only to weaken the thesis to something like the following: (T2) No contingent ought-statement is entailed by any consistent set of is-statements. Fair enough. The fact (if indeed it is a fact) that contradictions entail every statement and necessary truths are entailed by every statement is no longer a difficulty for the thesis. I wish to turn now to an entirely different, and far more interesting, obstacle faced by the revised thesis (T2).

Consider the following arguments: (1) (a) If Socrates knows that Plato ought to be a philosopher, then Plato ought to be a philosopher. (b) But Socrates does know that Plato ought to be a philosopher. (c) Hence, Plato ought to be a philosopher.

(2) (d) If Socrates is identical with the most distinguished teacher of Plato, then whatever Socrates ought to do, the most distinguished teacher of Plato ought to do.