What makes a complete sentence?
A complete sentence contains at least one independent clause: a clause that can stand alone. In an ordinary statement, it has a subject and a finite verb and expresses a complete idea.
Maya missed the bus.
Maya is the subject. Missed is the finite verb: it expresses past tense. This clause can stand alone.
A finite verb carries tense or works with the subject to form a verb phrase, such as missed, is waiting or has arrived. An -ing form on its own does not usually do this job.
Commands are complete sentences too: in “Close the window,” the subject you is understood.
Why a fragment is incomplete
A fragment is a group of words presented as a sentence even though it cannot stand alone as a complete sentence. A capital letter and a full stop do not make it complete.
A missing subject
Fragment: Walked home after school.
Repair: Maya walked home after school.
A missing finite verb
Fragment: Maya waiting at the bus stop.
Repair: Maya was waiting at the bus stop.
A dependent clause on its own
Fragment: Because Maya missed the bus.
Repair: Because Maya missed the bus, she walked home.
The fragment already has a subject and a finite verb. But because makes the clause dependent: the reader still needs the main statement.
Words such as although, when and if can also introduce dependent clauses. These clauses are useful parts of complete sentences when attached to an independent clause.
Completing a dependent-clause fragment
Fragment: Because the last bus had left.
Why it is incomplete: It gives a reason, but does not say what happened as a result. The dependent clause needs a main clause.
Completed sentence: Because the last bus had left, we walked home.
The added main clause, we walked home, completes the sentence. It can stand alone, while because the last bus had left explains the reason.
When the dependent clause comes first, it is usually followed by a comma. You can also put the main clause first: We walked home because the last bus had left.
Check the structure, rather than the length. A short sentence can be complete, and a long group of words can still be a fragment.
Try it: six questions
Choose whether each example is a complete sentence or a fragment. Check any answers you have selected. You can change your answers and try again.
Lesson inspired by Robin L. Simmons’s Grammar Bytes! presentation on fragments, comma splices and fused sentences. Examples and practice questions written for this toolkit.