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	🇨🇳 中文 词/短语	Definition	🇨🇳 中文 定义	Example	🇨🇳 中文 示例
Adverb clause	🧩 副词从句	Modifies time, reason, condition, contrast, purpose	🧩 修饰时间、原因、条件、对比、目的	I stayed home because I was sick.	🧩 我待在家，因为我生病了。
Adjective clause	🧩 形容词从句	Describes a noun or pronoun	🧩 描述名词或代词	The book that you lent me is great.	🧩 你借给我的那本书很棒。
Noun clause	🧩 名词从句	Functions as a noun in the sentence	🧩 在句子中充当名词的功能	What she said surprised everyone.	🧩 她说的话让每个人都感到吃惊。

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	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
Defining clauses do not use commas	📌 定义性从句不使用逗号	Students who study regularly improve faster.	📌 经常学习的学生进步更快。
Non-defining clauses use commas	📌 非限定性从句使用逗号	My brother, who lives in Chicago, is visiting.	📌 我哥哥，住在芝加哥的，正在来访。
That is common in defining clauses	📌 that 常用于定义性从句	The movie that we watched was long.	📌 我们看的那部电影很长。
Which is common in non-defining clauses	📌 which 常用于非限定性从句	The movie, which we watched yesterday, was long.	📌 那部我们昨天看的电影很长。

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	🇨🇳 中文 词/短语	Definition	🇨🇳 中文 定义	Example	🇨🇳 中文 示例
Coordinating conjunctions	🔗 并列连词	Join equal structures and often two independent clauses	🔗 连接同等结构，通常是两个独立从句	I called, and she answered.	🔗 我打电话了，她就回答了。
Subordinating conjunctions	🔗 从属连词	Introduce dependent clauses and show relationships	🔗 引入从属从句并展示关系	I left after the meeting ended.	🔗 会议结束后我离开了。
Relative pronouns and adverbs	🔗 关系代词和关系副词	Introduce relative clauses and refer to a noun	🔗 引入关系从句并指向名词	The person who called left a message.	🔗 打电话的人留下了信息。

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	🇨🇳 中文 规则	Example	🇨🇳 中文 示例
Independent clause + comma + coordinating conjunction + independent clause	📝 独立从句 + 逗号 + 并列连词 + 独立从句	She finished early, and she went home.	📝 她很早完成，然后回家。
Independent clause + semicolon + independent clause	📝 独立从句 + 分号 + 独立从句	She finished early; she went home.	📝 她很早完成；她回家了。
Dependent clause first usually needs a comma	📝 从属从句在前通常需要逗号	Because it was late, we stopped.	📝 因为天色已晚，我们停下。
Dependent clause after often does not need a comma	📝 从属从句在后通常不需要逗号	We stopped because it was late.	📝 我们停下，因为天色已晚。

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.