A clause is a group of words that contains a subject and a verb. Clauses can express a complete thought or an incomplete thought, depending on the type. Understanding clauses helps you build correct sentences and avoid sentence fragments. Clauses are the building blocks for simple, compound, complex, and compound-complex sentences.

Most clauses are built around a subject and a verb. The subject tells who or what the clause is about, and the verb shows an action or a state. A clause may also include objects, complements, and adverbials, but it is still a clause as long as it has a subject and a verb. In commands, the subject is often implied rather than stated.

An independent clause can stand alone as a complete sentence because it expresses a complete thought. It has its own subject and verb and does not depend on another clause for meaning. Independent clauses can be joined to form longer sentences, but each one is grammatically complete by itself. Punctuation and conjunctions determine how independent clauses connect.

A dependent clause has a subject and a verb but cannot stand alone as a complete sentence. It depends on an independent clause to complete its meaning. Dependent clauses often begin with a subordinating conjunction or a relative word, which signals that the information is attached to another clause. Dependent clauses add time, reason, condition, contrast, or extra description.

Dependent clauses come in three main types: adverb clauses, adjective clauses, and noun clauses. Adverb clauses function like adverbs by modifying a verb, adjective, or whole clause. Adjective clauses describe a noun or pronoun and are introduced by relative pronouns or relative adverbs. Noun clauses function like nouns and can act as subjects, objects, or complements.

Word/Phrase	Definition	Example
Adverb clause	Modifies time, reason, condition, contrast, purpose	I stayed home because I was sick.
Adjective clause	Describes a noun or pronoun	The book that you lent me is great.
Noun clause	Functions as a noun in the sentence	What she said surprised everyone.

A relative clause is a type of adjective clause that gives information about a noun or pronoun. It usually starts with who, whom, whose, which, that, where, or when. Relative clauses can be defining, meaning they identify exactly which person or thing, or non-defining, meaning they add extra information. The choice affects punctuation and whether the clause is essential.

Defining relative clauses are essential for identifying the noun, so they are not set off by commas. Non-defining relative clauses add extra, non-essential information and must be separated with commas. In general, that is common in defining clauses, while which is common in non-defining clauses, especially in formal writing. Using commas correctly changes meaning and clarity.

Rule	Example
Defining clauses do not use commas	Students who study regularly improve faster.
Non-defining clauses use commas	My brother, who lives in Chicago, is visiting.
That is common in defining clauses	The movie that we watched was long.
Which is common in non-defining clauses	The movie, which we watched yesterday, was long.

Clauses are connected with coordinating conjunctions, subordinating conjunctions, or relative words. Coordinating conjunctions join two items of equal grammatical status, often two independent clauses. Subordinating conjunctions introduce dependent clauses and show relationships like time, cause, and condition. Relative words introduce adjective clauses and link them to a noun.

Word/Phrase	Definition	Example
Coordinating conjunctions	Join equal structures and often two independent clauses	I called, and she answered.
Subordinating conjunctions	Introduce dependent clauses and show relationships	I left after the meeting ended.
Relative pronouns and adverbs	Introduce relative clauses and refer to a noun	The person who called left a message.

Punctuation depends on how clauses are combined. Two independent clauses can be joined with a comma plus a coordinating conjunction, or separated with a semicolon. A dependent clause is usually separated with a comma when it comes before the independent clause, but often no comma is used when it comes after. Relative clauses use commas only when they are non-defining.

Rule	Example
Independent clause + comma + coordinating conjunction + independent clause	She finished early, and she went home.
Independent clause + semicolon + independent clause	She finished early; she went home.
Dependent clause first usually needs a comma	Because it was late, we stopped.
Dependent clause after often does not need a comma	We stopped because it was late.

Clauses can fill different jobs inside a sentence. Some clauses form the main statement, while others act like single parts of speech. A noun clause can act as a subject, object, or complement. An adverb clause modifies how, when, why, or under what condition something happens, and an adjective clause modifies a noun.

A sentence fragment often happens when a dependent clause is written as if it were a complete sentence. To fix a fragment, attach the dependent clause to an independent clause or revise it into an independent clause. Not every long group of words is a clause, and not every clause is a complete sentence. Checking for an independent clause helps you edit for completeness and clarity.