Subordinating conjunctions join a subordinate clause (also called dependent clause) to an independent /main clause. Subordinating conjunctions introduce subordinate clauses that are less important than or less than equal to the main clause, although they do help in adding to the content of the main clause.
Subordinating conjunctions in use:
- The whole ostrich-rearing business will fail unless we put in more money.
- It’s urgent that something be done before more villagers are trampled to death by the elephants.
- These girls are already drunk although they have drunk only a little.
The above subordinate clauses are bolded and as can be seen, are introduced by subordinating conjunctions unless, before and although. They cannot stand independently as complete clauses. They have to be joined to their respective main clauses to make complete sentences.
(For more examples of subordinating conjunctions, see List 12 - Conjunctions.)