because / since / as
Naming a cause without mixing it with time.
Because is the plain word for a cause: We left because the hall was cold. Since may mean “from that time” or “because.” If both readings are possible, use because. As for a cause is weaker still and often reads as time: As the door closed, we sat down. Use because when the cause is the point.
Examples
Use The flight was late because the storm closed the runway.
Use Since June she has worked nights.
Avoid Since the storm closed the runway, the flight was late. (If a reader could take since as time.)