A subordinating conjunction connects a dependent clause to an independent clause. It signals that one clause is subordinate and cannot stand alone as a sentence. The subordinating conjunction usually appears at the start of the dependent clause. The combined structure forms a complex sentence. Punctuation may change based on the position of the dependent clause.

An independent clause expresses a complete thought and can stand alone as a sentence. A dependent clause contains a subject and a verb but does not form a complete thought on its own. Dependent clauses often answer questions like when, why, how, or under what condition. Subordinating conjunctions introduce dependent clauses. The main clause provides the core meaning of the sentence.

Some subordinating conjunctions indicate time, such as when and after. Others indicate cause or reason, such as because and since. Words like if and unless introduce conditions. Although and though express contrast. Where and wherever can introduce clauses about place.

Word/Phrase	Definition
because	This word introduces a reason or cause.
if	This word introduces a condition.
when	This word introduces a specific time.
although	This word introduces a contrast.
while	This word introduces simultaneous actions or contrast.
since	This word introduces a reason or a starting time.
after	This word introduces a later time.
before	This word introduces an earlier time.
unless	This word introduces an exception or negative condition.
where	This word introduces a place or location.

If the dependent clause comes before the independent clause, a comma usually separates the two clauses. If the independent clause comes first, a comma is usually not needed. The subordinating conjunction stays at the beginning of the dependent clause. The subject and verb order inside each clause remains standard. The choice of conjunction determines what information the dependent clause provides.

Rule
If a dependent clause comes first, use a comma before the independent clause.
If a dependent clause comes after the independent clause, do not use a comma in most cases.
Place the subordinating conjunction at the start of the dependent clause.

Subordinating conjunctions can show time by linking events or actions in sequence. They can show cause and effect by linking a result to a reason. They can show condition by linking an outcome to a requirement. They can show contrast by linking opposing ideas. They can show place by linking an action to a location.

Word/Phrase	Definition
time	This category links actions by when they happen.
cause/reason	This category links a result to its explanation.
condition	This category links an outcome to a possible situation.
contrast	This category links ideas that differ or conflict.
place	This category links an action to where it occurs.