Before can be used in the following ways: as a conjunction (connecting two clauses): Think carefully before you choose. as a preposition (followed by a noun): We moved to London before the war. as an adverb (without a following noun): I'd met him once before.
We use since as a subordinating conjunction to introduce a subordinate clause. We use it to give a reason for something: Sean had no reason to take a taxi since his flat was near enough to walk to. Since her husband hated holidays so much, she decided to go on her own.
