The punctuation rules that pay off.
Think in clauses. Once you can identify a complete sentence, punctuation becomes a decision you can explain.
Find the subject and verb
A complete independent clause has a subject, a finite verb, and a complete thought. 'Because the study ended' is dependent even though it has a subject and verb.
Join two complete thoughts
Use a period, a semicolon, or a comma plus a coordinating conjunction (for, and, nor, but, or, yet, so). A comma alone is not enough.
Check colons and interruptions
A colon normally follows a complete clause and introduces an explanation or list. Nonessential information needs a matching pair of commas, dashes, or parentheses when it occurs mid-sentence.
Keep the core sentence intact
Do not separate a subject from its verb or a verb from its object with a lone comma. Read the sentence without any interruption to check its structure.
Incorrect: The trial ended, the researchers analyzed the data. Correct: The trial ended; the researchers analyzed the data.