The word conjunction comes from a Latin root meaning "join." In grammar, a conjunction is a joining word.

There are three main types of conjunctions in English: coordinating, correlative and subordinating. This article focusses on subordinating conjunctions.

What is a subordinating conjunction?

A subordinating conjunction is a joining word that connects two clauses. (A clause is a word group containing a subject and a verb.)

How are subordinating conjunctions different from other conjunctions?

Other conjunctions join words, phrases or clauses of equal value.

A subordinating conjunction joins clauses of unequal value. The clause that begins with the subordinating conjunction is called a subordinate (or dependent) clause. It is less important than the other clause, which is called the main clause.

For example, consider these two clauses:

• Audrey lit up a cigarette.
• Henry grabbed the fire extinguisher.

These clauses are grammatically equal. They are both independent clauses (that is, they can stand alone as sentences).

But the clauses are not of equal value: they don't express equally important ideas. The second clause seems to be the main idea, and the first clause seems merely secondary. We can join these clauses of unequal value into a single sentence by placing the subordinating conjunction as at the beginning of the less important idea:

• As Audrey lit up a cigarette, Henry grabbed the fire extinguisher.

The first clause is now a subordinate or dependent clause. It is no longer grammatically equal to the main clause because it cannot stand alone. Therefore, it must be joined to the main clause so that the two clauses form a single sentence.

Such a sentence is called a complex sentence. A complex sentence is one that contains one main clause and at least one subordinate or dependent clause. The main clause expresses the primary idea, and the subordinate clause or clauses express secondary ideas.

Tip: You need to remember to join the subordinate clause to a main clause. Left by itself, a subordinate clause is a fragment, a common type of sentence error.

What words can act as subordinating conjunctions?

There are many subordinating conjunctions in English. Some of the most common are shown below, grouped by the relationships they express. In the examples, the conjunction is in bold font, and the subordinate clause introduced by the conjunction is in italics:

Cause:

as, because, since

Because Heinrich's joints were creaking, he oiled them.

Comparison:

as, than

Condition:

if, provided (that), unless

Lacey won't win the perogy-eating contest if she keeps eating faster than Hank can count.

Concession:

although, (even) though, whereas, while

Although Gordon watered his cactus regularly, it didn't thrive.

Manner:

as, as if, as though

Sylvester looked pleased, as if he had swallowed a canary.

Place:

where, wherever

Wherever the mice laugh at the cat, there you will find a hole. (Proverb)

Purpose:

in order that, so that

Jessica is learning to moonwalk so that she can become an astronaut.

Time:

after, as, before, once, since, till, until, when, while

Greta's letters are less regular since she moved to Come-by-Chance.

Other:

that (used to introduce a clause that functions as a noun)

Eric suspected that Lauren didn't like his new haircut when she offered to lend him her toque.

How are subordinating conjunctions different from prepositions?

Some subordinating conjunctions (especially those expressing time) can also act as prepositions. As prepositions, they introduce a prepositional phrase without a subject and verb:

• After dinner, we'll leave for the party.
• (prepositional phrase with no subject and verb)

As conjunctions, they introduce a clause containing a subject and verb:

• After we eat dinner, we'll leave for the party.
• (subordinate clause with subject we and verb eat)