Sentence Structure: Clauses & Sentence Types

Level B1 · Sentence Basics

A clause is any group of words that has at least a subject and a verb. She smiled is a clause; running late is not (no subject, no full verb). Every sentence is built from one or more clauses, and there are only two kinds. An independent clause can stand alone as a complete sentence (She smiled), while a dependent clause has a subject and a verb but cannot stand alone. It starts with a word that makes it incomplete, like because, although, who, or that (because she smiled is not a full sentence; it leaves you waiting for more).

Dependent clauses do different jobs inside a sentence:

• noun clause — acts like a noun, often as the object of a verb: I know that she left (compare: I know the answer).
• adjective clause (also called a relative clause) — describes a noun, usually introduced by who, which, or that: the man who called is my uncle. See the dedicated Relative Clauses topic for the full rules.
• adverb clause — describes when, why, where, or under what condition, introduced by words like because, although, when, or if: She left because she was tired.
• reduced clause — a dependent clause shortened by dropping the pronoun and be, often using -ing or a past participle: the man standing there (from who is standing there). See Participle Clauses for the full pattern.

Combining clauses gives four sentence types:

• simple — one independent clause, and nothing else: The rain stopped.
• compound — two or more independent clauses joined by a coordinating conjunction (and, but, or, so) or a semicolon: The rain stopped, and the sun came out. / The rain stopped; the sun came out.
• complex — one independent clause plus at least one dependent clause: The rain stopped after the storm passed.
• compound-complex — two or more independent clauses plus at least one dependent clause: The rain stopped after the storm passed, and the sun came out.

Punctuation changes with the sentence type. A comma before a coordinating conjunction joins independent clauses in a compound sentence: The rain stopped, and the sun came out. When a dependent clause comes first in a complex sentence, a comma follows it: After the storm passed, the rain stopped — but no comma is needed when the dependent clause comes second: The rain stopped after the storm passed.

The most common mistake is the comma splice: joining two independent clauses with only a comma, no conjunction and no semicolon. The rain stopped, the sun came out is a comma splice — it needs and, but, so, or a semicolon instead of the bare comma. A second frequent error is the sentence fragment: punctuating a dependent clause as if it were a full sentence, as in Because she was tired. She went home — the first part has a subject and verb but cannot stand alone; it must be joined to an independent clause: She went home because she was tired. A third error is the run-on sentence: joining two independent clauses with no punctuation or conjunction at all, as in The rain stopped the sun came out.

Check for a subject and a verb to confirm a clause exists, and check whether it starts with a word like because, although, when, if, who, which, or that — that word is the signal for a dependent clause. Count the independent clauses (does each part make sense alone?) and the dependent clauses to classify the sentence type, and check that commas, conjunctions, and semicolons match the pattern for that type.

Practice

Clause Types & Sentence Types · Fixing Comma Splices, Fragments & Run-Ons