The preposition governing a noun clause is frequently omitted.
(a) After the adjectives aware, certain, glad, sure, positive, etc., especially when used as predicate adjectives,—“When you saw a lad with that book on the desk before him, you might be sure, without asking, that he had deserved the master’s approval in some way.”—Annie Preston.
If a noun were used instead of a clause after sure, it would be introduced by a preposition; but it is English usage to dispense with the preposition when we use a clause, though the clause certainly answers the same question as the noun, viz., sure of what? In disposing of a clause so used, say that it is brought in by the adjective without the help of a preposition, or supply the preposition, or supply the phrase of the fact, disposing of the clause as an appositive of the noun fact.
(b) After such predicates as is determined, is convinced, is resolved, etc.—“I am convinced that every spring a large number of birds which have survived the southern campaign return to their old haunts to breed.”—Burroughs.
(c) After the verbs assure and warn,—“You very soon assure yourself that such springs are also fed by rain.”—Tyndall.
“He immediately discharged two muskets into the darkness, to warn the enemy that he knew of their presence and intention.”
(d) After some nouns like doubt, assurance, evidence, etc.—“Cæsar saw no evidence that the gods practically interfered in human affairs.”—Froude.
5. In apposition.—“We look not to the question whether a man have or have not children to be benefited by the education for which he pays.”—Webster. Here the clause makes definite the word question, a noun of wide application.
We occasionally come across sentences constructed like the following,—“What a man does, that he has.”—Emerson. The meaning is,—“A man has what he does,” the noun clause what he does being object of the verb has. But in the original sentence the pronominal that is object of has, and this indefinite object is explained by the noun clause what a man does, which is therefore to be called an appositive. Such an arrangement arises from a desire to make the clause prominent and also to hold the main thought in suspense until the end of the sentence.
6. Subjective complement.—“In fact, the only difference between one of these ice streams and an ordinary river is, that the former moves very slowly.”