1. I am sure that he will succeed.
2. I'm not sure that he will succeed.
3. I'm not sure if he will succeed.
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Are all grammatical? is 'that he...' a noun phrase or an adverbial phrase?
Is 'if he will...' a noun phrase or an adverbial phrase?
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4. I am sure (of) that he will succeed.
5. I'm not sure (of) that he will succeed.
6. I'm not sure (of) if he will succeed.
In each sentence, is 'the preposition 'of' missing?
1 answer
Yes, all of the sentences are grammatically correct. The phrase "that he will succeed" is an adverbial phrase, and the phrase "if he will succeed" is a noun phrase. In sentences 4, 5, and 6, the preposition "of" is optional and can be included or omitted.