dependent clause / independent clause
A clause that cannot stand alone versus one that can.
An independent clause can stand as a sentence: The train left. A dependent clause cannot: when the train left. A dependent clause needs an independent clause: When the train left, the hall was empty. A subordinating conjunction—because, if, when, although, unless, after, before, since, while—opens many dependent clauses.
Examples
UseIf the lock sticks, call her.
AvoidIf the lock sticks.