Searle's Derivation of Promissory Obligation

In “How to derive ‘ought’ from ‘is’” (Searle 1964), perhaps the most famous among his early articles, John Searle set out to show that what is sometimes called “the naturalistic fallacy”—the fallacy that is allegedly committed by those who affirm that it is possible to deduce evaluative conclusions from wholly nonevaluative (‘descriptive’) premises—is not at all a fallacy. The reason that it is not, Searle claimed, is that there are certain kinds of clearly evaluative statements (in particular, statements about what a particular person ought to do or has the obligation to do) that are logically deducible from certain sets of wholly non-evaluative (‘descriptive’) statements (specifically, from sets of statements that include a statement about what that person has promised to do). That being so, Searle contended, not only is there no such thing as “the naturalistic fallacy,” but those claiming that there is commit themselves to the denial of the validity of a series of logically impeccable inferences (and so become victims of what might be called “the naturalistic fallacy fallacy”).