 The first rule, MP-Narrow, is obviously not a rule with which we ought to comply: if q is obviously false, then it’s not the case that I ought to believe that q is true—not even if I believe that p is true, and that if p is true then q is true. Nonetheless, if q is obviously false, then (perhaps) I ought not both believe that p is true and also believe that if p is true then q is true. That’s because, even if MP-Narrow is not a rule with which we ought to comply, MP-Wide may still be such a rule. The difference between the two rules is in the scope of the “ought”: in MP-Narrow, its scope includes only one belief (viz., the belief that q is true), whereas in MP-Wide, its scope includes a combination of two beliefs (viz., that p is true, and that if p is true then q is true) and one lack of belief (viz., that q is true).