doubt

doubt verb.

1. I doubt whether he'll come and I doubt if he'll come are the standard constructions when doubt is used in the affirmative to mean ‘think it unlikely’. When doubt is used in the negative to mean ‘think it likely’, a that-clause is normal: I don't doubt that he'll come. The logic behind this difference is that when doubt is in the affirmative it implies uncertainty in the following clause (which is consistent with use of whether or if), whereas when it is used in the negative it implies probability in the following clause (which is more consistent with that).

2. This rationale lies behind the objection many people have to the increasing use of doubt, in the affirmative followed by a that-clause or by an object clause without a conjunction. This is commonly regarded as an Americanism, but it is attested in BrE use at the end of the 19c. Examples: (with that)

• Schiller doubted that a poetic measure could be formed capable of holding Goethe's plan —B. Taylor, 1871

• I doubt that the White House is responsible for this rash of tittle-tattle —Alistair Cooke, 1981

• I doubt that the okapi which died…would agree with Mark Twain that ‘Wagner is not as bad as he sounds’ —Independent, 1994

• (with object clause) He doubted Ferrari would sue him —New Yorker, 1986

• I doubt there was anything really wrong with him —Anita Brookner, 1992.