| doubt and doubtful with that, whether, or if. You can follow doubt and doubtful with clauses introduced by the conjunction that, whether, or if. Which conjunction you choose depends somewhat on the meaning you want to convey. We normally use whether to introduce indirect questions: I asked whether he could come along. Whether is therefore the traditional choice when the subject of doubt is in a state of genuine uncertainty about alternative possibilities: Sue has studied so much philosophy this year that she?s begun to doubt whether she exists. Similarly, when doubtful indicates uncertainty, whether is probably the word you want: At one time it was doubtful whether the company could recover from its financial difficulties, but the government loan seems to have helped. | 1 |
| On the other hand, you use that when you use doubt as an understated way of expressing disbelief. Thus you might say I doubt that we?ve seen the last of that problem, meaning ?I think we haven?t seen the last of that problem.? That is also the usual choice when the truth of the clause following doubt is assumed, as in negative sentences and questions. Thus I never doubted for a minute that I would be rescued implies ?I was certain that I would be rescued.? By the same token, Do you doubt that you will be paid? seems to pose a rhetorical question meaning ?Surely you believe that you will be paid,? whereas Do you doubt whether you will be paid? may express a genuine request for information and might be followed by Because if you do, you should make the client post a bond. | 2 |
| In other cases, however, this distinction between whether and that is not always observed, and that is frequently used as a substitute for whether. You can also use if as a substitute for whether, but if is more informal in tone. | 3 |
| doubt but. In informal speech, the clause following doubt is sometimes introduced with but: I don?t doubt but (or but what) he will come. This construction has been used by many fine writers, but modern critics sometimes object to its use in formal writing. | 4 |
| doubt with the subjunctive in if clauses. For a discussion of when to use the subjunctive in if clauses, such as those following doubt, see subjunctive under Grammar. | 5 |