Fix ACT English run-ons, comma splices, and fragments by counting independent clauses and choosing punctuation that legally joins or separates them.
Subject + verb that can stand alone as a sentence.
A dependent clause starts with because/although/when/if/which/that and cannot stand alone.
Two independent clauses with no punctuation (run-on) or only a comma (splice) = wrong.
Period, or semicolon, between the two independent clauses.
Comma + coordinating conjunction (for, and, nor, but, or, yet, so).
Subordinate one clause (add because/when/although…) so it attaches with a comma.
A large share of ACT English questions come down to one skill: knowing where one sentence should end and the next should begin. The test hides run-on sentences, comma splices, and fragments inside natural-sounding prose, then offers four ways to punctuate the boundary. You are never asked to label a clause; you are asked to choose the version that legally connects — or separates — the ideas. The way to win is to stop reading for "flow" and start counting independent clauses. Once you know how many complete sentences are packed into the underlined stretch, the correct punctuation follows automatically.
An independent clause has a subject and a verb and can stand alone as a sentence: "The ferry docked." A dependent clause also has a subject and a verb but begins with a word that makes it unable to stand alone — because, although, when, since, if, while, after, that, which, who. "Because the ferry docked" is dependent; it leaves you waiting for the rest. The entire topic hinges on telling these two apart, because two independent clauses need strong punctuation between them, while a dependent clause attaches to an independent one with just a comma or nothing at all.
Notice that run-ons and comma splices are the same underlying problem — two independent clauses with too little punctuation between them — and they share the same set of fixes.
When you have two independent clauses, exactly these four fixes are correct. Memorize them, because every right answer to a run-on or splice question is one of them:
Any choice that does something else — a bare comma, a comma plus a non-FANBOYS word like "however," or no punctuation at all — is wrong.
The reason these questions are hard is that the run-on often sounds fine, because in speech we barrel through boundaries without pausing. So do not trust your ear. Instead, when you hit an underlined junction, split the sentence at that point and ask two questions: Is the left side a complete sentence? Is the right side a complete sentence? If the answer to both is yes, you must use one of the four legal joins. If one side is a dependent clause or a fragment, a comma or no punctuation may be right, and a period or semicolon would strand a fragment.
Take: "The archaeologists uncovered a mosaic floor, it had lain hidden beneath the plaza for centuries." Split at the comma: "The archaeologists uncovered a mosaic floor" (complete) and "it had lain hidden beneath the plaza for centuries" (complete). Two independent clauses with only a comma — a splice. Fix it with a period, a semicolon, "…floor, and it had lain…," or "…a mosaic floor that had lain…" (making the second clause dependent).
The ACT also tests the reverse mistake — chopping a single sentence into pieces. "The volunteers cleared the trail. Working from dawn until the last light faded." The second "sentence" has no subject that can stand on its own; "Working…" is a fragment. The fix is to reconnect it: "The volunteers cleared the trail, working from dawn until the last light faded." When a choice offers a period or semicolon, always confirm both resulting pieces are complete sentences; if one is a fragment, that choice is wrong even though it "looks" grammatical.
Choose the best version: "The alarm rang across the campus ___ students filed calmly out of every building." (NO CHANGE: campus students / campus, and students / campus, students / campus students,)
Choose the best version: "The recipe looked simple ___ it took the whole afternoon to prepare." (NO CHANGE: simple, it took / simple; it took / simple it took / simple, it, took)
Choose the best version: "The river rose past its banks ___ the town opened the emergency shelters early." (NO CHANGE: banks the town / banks, the town / When the river rose past its banks, the town / banks, however the town)
Choose the best version: "The crew repainted the entire mural in a weekend. ___ using scaffolding borrowed from a neighboring theater." (NO CHANGE: weekend. Using / weekend, using / weekend; using / weekend. They used)
Choose the best version: "For nearly a decade the observatory catalogued faint, slow-moving objects near the edge of the solar system ___ its data eventually helped astronomers confirm the existence of a distant dwarf planet." (NO CHANGE: system, its data / system its data / system, and its data / system, its data, which)
Choose the best version: "The engineers rerouted the failing pipeline in a single night. ___ prevented a spill that could have reached the reservoir." (NO CHANGE: night. Which / night, which / night; which / night, and which)
Trusting your ear — accepting a run-on because it reads smoothly in your head.
Split the sentence at the junction and test each side for completeness. Speech ignores boundaries; grammar does not.
Thinking "comma + however" (or "comma + therefore") legally joins two sentences.
Only the seven coordinating conjunctions (for, and, nor, but, or, yet, so) join clauses after a comma. "However" needs a semicolon before it.
Choosing a period or semicolon that leaves a fragment on one side.
Before accepting a period or semicolon, confirm BOTH resulting pieces are complete sentences. If one is a fragment, reconnect it with a comma instead.
Assuming a very long clause is too big to be part of a comma splice.
Length is irrelevant. Count independent clauses; two of them with only a comma between is still a splice, no matter how many words fill each one.
The volcano had been dormant for centuries ___ a thin plume of ash now drifted steadily from its summit.
Which choice best fits the conventions of Standard English?
The museum extended its hours for the exhibit ___ thousands of visitors still had to be turned away each evening.
Which choice best fits the conventions of Standard English?
The power failed across three counties during the storm ___ the hospital switched instantly to its backup generators.
Which choice best fits the conventions of Standard English?
The trail crew rebuilt the washed-out footbridge in record time. ___ hauling every timber up the ridge on their backs.
Which choice best fits the conventions of Standard English?
For three summers the biologists tracked the wolf pack across the vast northern preserve ___ their long records finally revealed how the animals shifted range in response to a warming climate.
Which choice best fits the conventions of Standard English?
The technicians recalibrated the telescope's mirror over a single sleepless weekend. ___ restored the razor-sharp images the instrument had lost after the earthquake.
Which choice best fits the conventions of Standard English?
Master ACT English comma questions by testing whether the underlined comma marks a real boundary — an interrupter, a list, a joined clause — instead of guessing by pauses.
Learn the ACT English rules for semicolons, colons, and dashes by testing what sits on each side of the mark — a full sentence, a list, or an interruption.
Master ACT English transition questions by reading the two ideas a connector joins — contrast, cause, addition, or sequence — instead of picking a word that merely sounds smooth.