A subordinating conjunction, also called a dependent word or subordinator, is a word that joins a dependent clause and an independent clause. In English, it appears at the beginning of, and establishes the nature of, a subordinate clause.
Subordinatingconjunction definitions are similar to the better studied noun and verb definitions in having a genus term and differentiae.
Subordinatingconjunctions with this pattern thus appear to be characterizing the subordinate clause.
Subordinatingconjunctions essentially characterize the relation between the subordinate and main clauses, and generally characterize some of the temporal features associated with one or both of the clauses.
Sentences using subordinatingconjunctions to combine clauses follow one of two basic formulas: one in which the dependent clause comes first, and one in which the dependent clause comes second.
This is the incomplete condition that the subordinatingconjunctions create, so if you ever use a word in a sentence, and it creates a condition similar to this one, you will know that this is a dependent clause and must be joined to an independent clause.
When you use a subordinatingconjunction to combine two simple sentences into a larger, more complicated one, it is (not surprisingly) called subordination.