Check for a complete clause
An independent clause contains a subject and a finite verb and can stand on its own as a sentence. The archive moved is complete. Although the archive moved leaves the reader waiting for a main clause because although makes it dependent. Before comparing punctuation choices, identify the grammatical structure on each side of the blank.
The archive moved; the city renovated its former building contains two independent clauses. A semicolon can join them. A comma alone cannot normally perform that job: The archive moved, the city renovated its former building is a comma splice. A comma plus a coordinating conjunction, such as and, can also join the clauses.
Do not treat every connector as a conjunction
Words such as however and therefore express relationships but do not join independent clauses in the same way as and, but, or so. The experiment failed, however, the team continued is a comma splice. A boundary such as a semicolon before however can fix it when the surrounding sentence supports that structure.
The experiment failed, but the team continued works because but is a coordinating conjunction. When evaluating a blank, include any words that are already printed after it. Choosing a semicolon without noticing a following coordinating conjunction may produce an inappropriate structure.
A colon needs a complete introduction
A colon can introduce a list or explanation after a complete clause. The curator displayed three materials: paper, cloth, and wood is valid because the words before the colon stand alone. The materials included: paper, cloth, and wood improperly separates the verb included from its object.
The words after a colon do not have to form an independent clause. A list or an explanatory phrase can follow it. This is one reason a colon and a semicolon are not interchangeable. A semicolon joining clauses requires an independent clause on each side.
Sometimes the right answer adds no punctuation
Do not put a comma between a subject and its verb merely because the subject is long. The samples collected from the river contained sediment keeps the subject and verb together. Of the river or collected from the river does not create a new sentence boundary by itself.
Supplementary information often uses paired commas. In The library, which opened last spring, hosts a reading group, the two commas enclose the which clause. If one comma is already present after the clause, look for the matching opening boundary.
Work through the punctuation topic without rushing. Explain what lies on each side of every mark. Your eventual aim is to recognize the structure quickly, but practicing an unreliable shortcut faster will only repeat the same mistakes.
Put the idea into practice.
Try eight original questions with explanations after each answer.
Practice this skill →References and further practice
References establish the test context. The examples and teaching explanations here are original. See our methodology for coverage and limitations.