How to fix run-on sentences on the ACT

A run-on happens when two complete sentences are joined without the right punctuation, and you fix it with one of four moves: a period, a semicolon, a comma plus a coordinating conjunction, or turning one clause into a dependent clause. That is the entire skill. Once those four fixes are automatic, a surprising number of ACT English questions stop being judgment calls and start being quick decisions.

The two flavors of run-on

A fused sentence jams two independent clauses together with no punctuation at all: The rain started early we moved the party inside. A comma splice uses a comma where a comma is not strong enough: The rain started early, we moved the party inside. Both are wrong for the same underlying reason, which is that a comma by itself cannot hold two complete sentences together. If you want to go deeper on the second kind, the details live in the guide to comma splices.

The four fixes

Take The rain started early we moved the party inside and watch how each fix changes the feel of the sentence without changing the facts.

• Period: The rain started early. We moved the party inside.
• Semicolon: The rain started early; we moved the party inside.
• Comma plus a coordinating conjunction: The rain started early, so we moved the party inside.
• Subordination: Because the rain started early, we moved the party inside.

The coordinating conjunctions are for, and, nor, but, or, yet, and so. Subordination means adding a word like because, although, when, since, or while to the front of one clause so it can no longer stand alone.

Why period and semicolon are the same answer

Here is a shortcut that saves real time. A period and a semicolon do the same grammatical work, so if both appear as answer choices with nothing else different between them, neither one can be correct. A question can only have one right answer, and those two would both be right. Use that to eliminate a pair instantly and spend your attention on the choices that actually differ. The same logic applies to semicolon questions generally.

More correct and incorrect pairs

• Incorrect: Dr. Okafor studies coral reefs she spends her summers in Belize. Correct: Dr. Okafor studies coral reefs, and she spends her summers in Belize.
• Incorrect: The recipe looked simple, it took four hours to finish. Correct: Although the recipe looked simple, it took four hours to finish.
• Incorrect: He forgot his calculator, however, he finished the section anyway. Correct: He forgot his calculator; however, he finished the section anyway.

Common traps and how the ACT tests run-ons

The biggest trap is the transition word. Words like "however", "therefore", "moreover", and "consequently" feel like they should be able to glue sentences together, but they are adverbs, not conjunctions. Putting one after a comma between two complete clauses still leaves you with a splice. Only the seven coordinating conjunctions can do that job with a comma.

The second trap is length. A run-on does not have to be long, and a long sentence is not automatically a run-on. Some perfectly correct sentences run thirty words with a single clause plus a pile of phrases, and some run-ons are eight words. Count clauses, not words.

The third trap is meaning. When two or three answer choices are all grammatically legal, the test is asking which relationship between the ideas makes sense. But and so point in different directions, and only one will fit the passage. Sentence structure and punctuation both sit inside Conventions of Standard English, which is 38 to 43% of the English section, and because the enhanced ACT attaches an explicit question stem to every item, you will usually know up front whether you are being asked about punctuation or about the logic of the connection.

A drill that builds the reflex

Write one fused sentence, then rewrite it all four ways. Do that with three different sentence pairs and you will have twelve rewrites, which is enough to make the moves feel physical rather than theoretical. Then, on your next practice passage, stop at every comma and ask whether both sides could stand alone as sentences. If they could, the comma needs help. thirty-six has concept quizzes that isolate this exact decision so you are not hunting for run-ons one at a time inside full passages. There is no penalty for a wrong answer on the ACT, so even when a sentence is genuinely close, pick the best option and move on rather than burning time. When you want the wider set of punctuation rules in one place, see the punctuation rules tested on ACT English.

This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.