A clause is a group of words with a subject and a verb. A clause can sometimes stand alone as a complete sentence. English uses clauses to build simple, compound, and complex sentences. The main difference is whether the clause can stand alone or depends on another clause.

An independent clause has a subject and a verb and expresses a complete idea. It can stand alone as a sentence or combine with another independent clause. In writing, independent clauses are often joined with a comma and a coordinating conjunction or with a semicolon.

Rule
An independent clause can stand alone as a sentence.
Two independent clauses can be joined with a coordinating conjunction.
Independent clauses can be joined with a semicolon when the ideas are closely related.

Coordinating conjunctions join two independent clauses in a compound sentence. English has seven main coordinators. They usually appear between the two clauses they connect.

Word/Phrase	Definition
and	‘And’ connects similar or related ideas.
but	‘But’ shows contrast between two ideas.
or	‘Or’ presents a choice between ideas.
nor	‘Nor’ connects negative alternatives.
for	‘For’ gives a reason, similar to ‘because’.
yet	‘Yet’ introduces a surprising contrast.
so	‘So’ shows a result or consequence.

A dependent clause has a subject and a verb but does not express a complete idea by itself. It cannot stand alone as a sentence. Dependent clauses often begin with subordinators, which signal their role in the sentence.

Rule
A dependent clause cannot stand alone as a complete sentence.
A dependent clause attaches to an independent clause to form a complete sentence.
Subordinators often mark a clause as dependent.

Subordinators introduce dependent clauses and show the relationship to the main clause. Common subordinators express time, cause, condition, contrast, and purpose. The choice of subordinator determines the meaning link between the clauses.

Word/Phrase	Definition
because	‘Because’ introduces a reason.
if	‘If’ introduces a condition.
when	‘When’ introduces a time.
although	‘Although’ introduces a contrast.
so that	‘So that’ introduces purpose.

A complex sentence combines an independent clause with one or more dependent clauses. The dependent clause can come before or after the independent clause. When a dependent clause comes first, a comma usually separates it from the independent clause.

Rule
A complex sentence includes one independent clause and at least one dependent clause.
A comma usually follows a dependent clause at the beginning of a sentence.
The meaning changes depending on which subordinator you use.

A relative clause is a dependent clause that describes a noun. It often starts with ‘who’, ‘which’, or ‘that’. Relative clauses help add information without starting a new sentence.

Word/Phrase	Definition
who	‘Who’ introduces a clause describing a person.
which	‘Which’ introduces a clause describing a thing or idea.
that	‘That’ introduces a clause describing a person or thing, often in essential information.

English divides relative clauses into restrictive and non-restrictive types. Restrictive clauses give essential information and usually use ‘that’ without commas. Non-restrictive clauses give extra information and use ‘which’ or ‘who’ with commas.

Rule
A restrictive relative clause gives essential information and does not use commas.
A non-restrictive relative clause gives extra information and uses commas.
‘That’ is typically used for restrictive clauses.
‘Which’ is typically used for non-restrictive clauses.

A noun clause is a dependent clause that functions as a noun in a sentence. It can act as a subject, object, or complement. Noun clauses often begin with ‘that’, ‘what’, ‘how’, ‘whether’, or ‘why’.

Word/Phrase	Definition
that	‘That’ introduces a clause stating a fact or belief.
what	‘What’ introduces a clause referring to a thing or idea.
how	‘How’ introduces a clause about a manner or way.
whether	‘Whether’ introduces a clause about alternatives or uncertainty.

Clauses are the building blocks of English sentences. Independent clauses can stand alone or combine in compound sentences. Dependent clauses need an independent clause and form complex sentences, including relative and noun clauses.