Subordinating Conjunctions join an independent clause to a dependent clause to form a complex sentence. The independent clause is the main clause, and the dependent clause is subordinate to the independent clause. Subordinating conjunctions show the type of relationship between the two clauses they join. They often indicate conditions, cause-and-effect, and relationships of time and place.

There are many subordinating conjunctions. Here are some common ones:

after	by the time	lest	since	when
although	even	now	so	whenever
as	even if	now that	so that	where
as if	even though	once	supposing	whereas
as long as	if	only	than	wherever
as much as	if only	only if	that	whether
as soon as	inasmuch	provided	though	whether or not
as though	in order that	provided that	till	which
because	in the event that	providing	unless	while
before	just as	rather than	until

Two independent clauses may be combined with a subordinating conjunction to form a complex sentence. However, once the subordinating conjunction has been added to a clause, it is no longer independent and depends on the other clause to complete its meaning. When forming complex sentences, it does not matter which clause comes first.

Randal could not go to his friend’s house. He failed his test.

Because Randal failed his test, he could not go to his friend’s house.

Randal could not go to his friend’s house because he failed his test.

Once the subordinating conjunction is attached to a clause, it can no longer stand alone but depends on the other. Notice that when putting the dependent clause first as an introductory statement, it must be set apart from the main clause with a comma. When the subordinating conjunction is placed in the middle of the sentence, there is generally no need for a comma. Here are a few more examples. Of subordinating conjunctions in action.

Sam put the groceries away as soon as he got home.

As soon as shows a time relationship between the two clauses.

Todd bought some overpriced snacks at the gas station so that he would not have to go hungry.

So that indicates that the second clause is a reason for the first.

Mom always brings extra snacks on road trips in case we get hungry.

In case sets up the second clause as a conditional reason for the action taken in the first clause.

Once the movie is over, we will go out for some chicken.

Once has the same meaning as as soon as in the first example.

We’ll go out for pizza as long as the kids behave at the reunion.

As long as makes the second clause a condition that must be met in order for the first clause to happen.