Sentence Structure: The Basics

Every sentence-structure question comes down to one check: is this a complete sentence?

A clause has a subject and a verb. An independent clause can stand alone: "The students packed up." A dependent clause cannot, because of the word it starts with — because, although, since, when, while, if. "When the bell rang" leaves you waiting.

A fragment is a piece punctuated like a sentence that is not one. Fix it by attaching it to a complete sentence: When the bell rang, the students packed up. When the dependent clause comes first, put a comma after it.

A run-on is the opposite problem: two complete sentences pushed together without the right punctuation. Fix it with a period, a semicolon, or a comma plus a FANBOYS word (for, and, nor, but, or, yet, so).