A practical english grammar - Vyssaja skola 1978
LINKING VERB + COMPLEMENT + THAT-dause
Sound symbols
Clauses introduced by that can be used to qualify structures consisting of linking verbs and their complements.
We are glad that you are here.
I am certain that he speaks English.
Notice that if the that-clause is replaced by a simple noun, a preposition is required.
We are glad of that.
I am certain of it.
Even though that-clauses of this type are usually analyzed as noun constructions in English, in sentences like these they seem to function adverbially.
Verbs like inform and convince behave somewhat similarly.
He informed me that you were here.
He informed me of your presence.
This convinces me that you are right.
This convinces me of your accuracy.
One rule must be remembered: that-clauses are not normally used after prepositions in English. If a preposition is absolutely required by the sentence, then the words “the fact,” “the report,” or the like are inserted before the that-clause.
I am amazed by the fact that you haven’t heard this before.
People still believe the story of George Washington and the cherry tree, in spite of the fact that historians have shown over and over again that it is nothing but a legend.