Prepositions can be followed by conjunctions in some cases but not in others.
indirect speech: prepositions dropped before that
Prepositions are not used directly before the conjunction that. In indirect speech – after words that refer to saying, writing, thinking etc –
prepositions are usually dropped before that-clauses. Compare:
I knew about his problems.
I knew that he had problems.
(NOT I knew about that he had problems.)
She had no idea of my state of mind.
She had no idea that I was unhappy.
(NOT She-had-no-tdeet-ofthat I wm-tmhappy.)
I wasn’t aware of the time.
I wasn’t aware that it was so late.
(not I wasn’t aware of-that tt-was-so-late.)
emotional reactions: prepositions dropped
Prepositions are also dropped before that after many common words that refer to emotional reactions. Compare:
We are sorry about the delay. – I was surprised at her strength.
We are sorry that the train is late. I was surprised that she was so strong. (NOT … sony about that the train- (NOT .. .surprised at that-she-tms-…) islate:)
the fact that
In other cases (not involving indirect speech or words referring to emotional reactions) prepositions cannot so often be dropped before Ј/zaЈ-clauses.
Instead, the expression the fact (see that-clauses.3) is generally put between the preposition and that.
The judge paid a lot of attention to the fact that the child was unhappy at home, (NOT The-judge paid a lot of attention (to) -tlm-t the child …)
He said the parents were responsible for the fact that the child had run away, (NOT … responsible -(for-)- -thaFthe-ehUd had-run away.)
question words
After some very common words like tell, ask, depend, sure, idea, look, prepositions can be dropped before who, which, what and other question
words. This is especially common in indirect questions. Compare:
Tell me about your trip.
Tell me (about) where you went.
I asked her about her religious beliefs.
I asked her whether she believed in God.
(More natural than I asked her about whether she believed in God.)
We may be late – it depends on the traffic.
We may be late – it depends (on) how much traffic there is.
I’m not sure of his method.
I’m not sure how he does it.
(More natural than I’m not sure of how he does it.)
Look at this.
Look (at) what I’ve got.
In other cases it is unusual or impossible to leave out the preposition.
I’m worried about where she is. (NOT I’m worried-wkere-sheHs.)
The police questioned me about what I’d seen.
There’s the question of who’s going to pay.
(More natural than … the question who’s going to pay.)
People’s chances of getting jobs vary according to whether they live in the North or the South, (NOT … according whether …)
If
does not normally follow prepositions; we use whether (see whether and if) instead. I’m worried about whether you’re happy, (NOT I’m worried-about
if …)
For the structures (with and without preposition) that are possible after a particular verb, noun or adjective, see a good dictionary.
For more information consult a good dictionary like Langman, Oxford, Merriam Webster, or Collins.