2 Sentence Structure and Boundaries

What makes a complete sentence

A complete sentence expresses a complete thought. In standard written English, it usually contains at least one independent clause: a group of words with a subject and a predicate that can stand alone.

Subjects and predicates

The subject names who or what the sentence is about. The predicate tells something about the subject and includes a verb. Both may contain more than one word, and a predicate may also include objects or descriptions.

For example, in The small bird sang a cheerful song in the tree, The small bird is the subject and sang a cheerful song in the tree is the predicate. To identify the subject, ask who or what performs the action or is described. To identify the predicate, locate the verb and ask what the subject does or is.

In a command, the subject is often understood to be you: “Close the door” means “You close the door.”

Clauses and their connections

A clause has a subject and a predicate. An independent clause expresses a complete thought and can stand alone, as in Maya finished her book. A dependent clause has a subject and predicate but does not express a complete thought on its own, as in because Maya finished her book.

A dependent clause must be joined to an independent clause: Because Maya finished her book, she returned it to the library. When the dependent clause begins the sentence, place a comma after it. When it follows the independent clause, a comma is usually unnecessary: She returned the book because she had finished it.

Basic sentence patterns

Basic sentence patterns describe how the subject and verb work with other parts of a sentence:

• Subject + verb (S–V): Leaves fell. Nothing is needed after the verb to complete the idea.

• Subject + verb + object (S–V–O): Nina opened the window. The object receives the action.

• Subject + linking verb + complement (S–V–C): The window seems stuck. The complement describes or identifies the subject.

• Subject + verb + indirect object + direct object (S–V–IO–DO): Nina gave Leo a note. The indirect object receives the direct object.

Extra details do not necessarily change the core pattern. In After lunch, Nina carefully opened the window, the core pattern remains subject + verb + object.

Simple, compound, and complex sentences

Sentence structure depends on how independent and dependent clauses are combined.

• Simple: One independent clause. It may have a compound subject or verb; for example, Kai and Jo laughed is simple.

• Compound: Two or more independent clauses. Join them with a comma and a coordinating conjunction (and, but, or, nor, for, so, or yet), or with a semicolon. For example: Kai laughed, but Jo stayed serious.

• Complex: An independent clause and at least one dependent clause. For example: Although Jo stayed serious, Kai laughed.

Sentence length does not determine structure. One long clause can still be simple, while two short independent clauses can make a compound sentence.

Recognizing sentence fragments

A sentence fragment is written as a sentence but lacks an independent clause. It may be missing a subject, a complete verb, or a complete thought.

• Missing subject: Ran to the bus. Add one: Tariq ran to the bus.

• Missing complete verb: The players practicing outside. Complete it: The players were practicing outside.

• Dependent clause alone: Although the road was icy. Complete the thought: Although the road was icy, we drove slowly.

When editing, check that each sentence has a subject and a complete predicate, and that at least one clause can stand alone.

Run-ons and comma splices

A run-on sentence incorrectly joins independent clauses. A fused sentence has no punctuation between the clauses: The rain stopped the sun came out. A comma splice joins them using only a comma: The rain stopped, the sun came out. A comma by itself does not join two independent clauses.

Correct these joins by separating the ideas, using a comma and coordinating conjunction, or using a semicolon when the ideas are closely related:

• The rain stopped. The sun came out.

• The rain stopped, and the sun came out.

• The rain stopped; the sun came out.

Checking sentence boundaries

For each sentence, identify the subject and predicate, then locate its clauses. Ask:

1. Does it contain a complete subject and verb?

2. Is at least one clause independent?

3. If it has multiple independent clauses, are they joined or separated correctly?