A subordinate clause, otherwise known as a dependent clause or a relative clause is a phrase that must be attached to an independent clause — a series of words that can stand on its own as a sentence —in order for a sentence to make grammatical sense. You can expand a simple sentence by adding a subordinate clause.  It makes the sentence more interesting.

A subordinate clause is a part of a sentence which contains at least one independent and one dependent clause. While an independent clause does not need another clause in order for it to make sense while a subordinate clause is so called because it is in relation to the main, independent clause.  It modifies the noun that is referred to in the independent clause.

A subordinate clause uses a subordinating conjunction at the beginning of the subordinate clause. Subordinating conjunctions are:
after, since, although, so that, as, though, as if, till, as long as, unless, as though, until, because, when, before, whenever, even though, where, if, wherever, whose, who, once, while, provided, whether. For example:
“After Christmas, they went back to work.”
“Although I’m not able to go to the show, I’ll join you for dinner .”
“As you can see, the weather has improved.”
“When we turn 60, movies will be half-price.”
“In case I do not make it, please say hello to Clare for me.”

Subordinate clause in quotes and lyrics

“Personally I’m always ready to learn, although I do not always like being taught.” Winston Churchill
“If I fell in love with you, would you promise to be true?” The Beatles

Subordinate clauses, which can’t stand alone, have three main purposes:

• to  describe nouns and pronouns
• to describe verbs, adverbs, and adjectives
• to act as the subject or object of another clause.

A subordinate clause, otherwise known as a dependent or a relative clause is a phrase that must be attached to an independent clause — a series of words that can stand on its own as a sentence —in order for a sentence to make grammatical sense.