Comma splices, run-on sentences, fragments and the passive voice: the four sentence faults and their repairs

A comma splice is two complete sentences joined by a comma and nothing else: The titration ran long, we skipped the discussion questions. Each half could stand alone, so the comma is not enough. Three repairs: a full stop (ran long. We skipped), a semicolon (ran long; we skipped), or a comma with a joining word (ran long, so we skipped). A run-on is the same fault with no comma at all; a fragment is a piece of a sentence standing alone; the passive voice is not a fault at all until it hides who did what. Each is shown broken and mended below.

The one idea under three of the faults: a clause that can stand alone

A clause is a group of words with a subject (who or what) and a finite verb (a verb with a tense: ran, leaked, was). When the two together make a claim, the clause is complete and can stand alone as a sentence. The test is one question: can I put a full stop after this and have it make sense on its own? The titration ran long. Yes. Because the titration ran long. No; the reader is waiting for the rest.

Length is not the test. It leaked. is two words and complete. A forty-word string of phrases with no finite verb is a fragment however long it is. Everything on this page except the passive comes back to that one question, which is why the Academic Writing course treats the three as one idea, sentence boundaries: fragments, run-ons and comma splices. The SAT Reading and Writing section tests the same boundary under its punctuation idea, commas, semicolons, colons and apostrophes: many of its questions are a splice or a fragment with four ways to punctuate it, one of which is right.

The comma splice, and three ways to mend it

The titration ran long, we skipped the discussion questions. Two complete clauses, one comma, no joint. Three repairs, and when to choose each:

1. A full stop. The titration ran long. We skipped the discussion questions. Two sentences. Choose it when the two ideas are separate, or when the second deserves its own weight.
2. A semicolon. The titration ran long; we skipped the discussion questions. One sentence, two balanced halves. Choose it when the halves belong together and no joining word says how. Semicolon vs comma in one line: a semicolon can join two complete clauses on its own; a comma cannot.
3. A comma and a coordinating word. The titration ran long, so we skipped the discussion questions. The seven coordinating words (the ones that can join two complete clauses with a comma) are and, but, so, or, yet, for, nor. Choose this when the relation between the halves is simple and you can name it.

A fourth, worth one line: make one half depend on the other. Because the titration ran long, we skipped the discussion questions. The first half is no longer a complete clause, so the comma is doing a job it can do.

The splice that catches everyone: however

The pilot raised attendance, however the buses cost more. This is the comma splice a Grade 12 marker sees most, because however feels like but. It is not. However, therefore, moreover, consequently, then and their relatives are adverbs (words that modify a clause), not joining words. A comma before one of them cannot join two complete sentences, and the sentence above is two.

The fix is a semicolon before and a comma after: The pilot raised attendance; however, the buses cost more. Or a split: The pilot raised attendance. However, the buses cost more. Or swap in the coordinating word it was pretending to be: The pilot raised attendance, but the buses cost more. The whole family of these words, grouped by the move each makes, is the transition-word table; every one of them joins by semicolon or full stop, never by comma alone.

The run-on (fused) sentence

The burette leaked the reading was low. Two complete clauses with nothing between them at all. Grammar books call it a fused sentence; most teachers write "RO". The same three repairs mend it: The burette leaked. The reading was low. / The burette leaked; the reading was low. / The burette leaked, so the reading was low.

The honest line: a run-on is not a long sentence. A long sentence with its joints in place is grammatical and may be good. A run-on is two sentences with no joint, and it can be nine words long. When a marker writes "run-on" beside a sentence that is merely long and muddled, the fix is usually to find the two or three claims inside it and give each its own sentence; the punctuation then takes care of itself.

The fragment, and when a fragment is fine

Three fragments turn up in most drafts, each ours, each with its fix:

• A dependent clause alone. Because the burette leaked. The reader waits for what happened. Attach it: Because the burette leaked, the reading was low. Or to the sentence before: The reading was low because the burette leaked.
• A participle phrase alone. Lowering the reading by two millilitres. No subject, no finite verb. Give it both: The leak lowered the reading by two millilitres.
• A which clause alone. Which explains the low result. Replace which with this: This explains the low result. Or attach it to the sentence before with a comma.

The honest paragraph. A deliberate fragment is a device in narrative and in speech: Not tonight. lands because it breaks the pattern. In an essay or a lab report, write the sentence. The marker cannot tell a deliberate fragment from a mistake, and in formal prose the pattern is the point. Run the test from the first section: full stop after it, does it stand? If not, it needs a home.

Active and passive voice: what each is

The Academic Writing course's idea 17, active and passive voice, is defined by what the subject does, not by the length of the verb. In the active voice the subject acts: The student read the burette at eye level. In the passive voice the subject is acted on: The burette was read at eye level by the student. The thing done has moved to the front, and the doer has moved to the end or vanished.

The test: add by someone after the verb. If it fits, the verb is passive. The burette was read [by someone] fits. The student read [by someone] does not.

The passive costs three things: length (two extra words at least), a hidden actor (the by phrase can be dropped, and often is) and a flat rhythm when every sentence does it. It buys two: the thing done goes first, which is right when the thing done is the topic, and the actor can be left out when it is unknown or does not matter. Say it plainly: the passive is grammatical English. A marker's "passive" note means you hid the actor and the actor mattered, not you broke a rule.

When the passive is the right choice

The method section of a lab report: The solution was heated to 60 °C. The reader does not care who held the beaker; the solution is the topic. The convention is the passive, and the lab report's method section shows it in a full report. When the actor is unknown: The sample was contaminated. Nobody knows by whom, and the sentence is honest about that. When the receiver is the paragraph's topic: in a paragraph about the burette, The burette was rinsed, filled and read keeps the burette in front where the reader is looking.

When it is the wrong choice. Hiding responsibility: Mistakes were made in the recording of the volumes is a sentence built to avoid saying who made them. The long chain of was ... by in an argument paragraph, where every sentence could have been active and shorter. The SAT names this under its idea concision and precision: a passive that adds words without adding meaning is exactly the thing the test asks you to cut, and SAT Reading and Writing practice has the rest of that section.

Two paragraphs, one before and one after

A paragraph of ours from a lab report, carrying all four faults, then the mended version. The faults are numbered so you can match them.

Before. (1) The titration was begun by our group at 9:40, the burette had been rinsed with water. (2) The first reading was low the second was closer to the expected value. (3) Which we did not notice until the third trial. (4) Mistakes were made in the recording of the volumes. (5) We repeated the trial, however the result did not change. (6) Because the burette still leaked.

What is wrong: (1) a comma splice, and a passive that hides who rinsed the burette with water instead of with the acid; (2) a run-on; (3) a which fragment; (4) a passive hiding the actor; (5) the however splice; (6) a dependent clause alone.

After. (1) Our group began the titration at 9:40 after rinsing the burette with water rather than with the acid. (2) The first reading was low; the second was closer to the expected value. (3) We did not notice the difference until the third trial. (4) We recorded two of the volumes wrongly. (5) We repeated the trial; however, the result did not change, (6) because the burette still leaked.

The mended paragraph is not much shorter. It is clearer, which is the point: the reader now knows who rinsed what, which reading was which, and why the result stuck. Notice that one passive could have stayed: the burette had been rinsed with water is fine in a method section where the burette is the topic. It was changed here because the sentence's job was to say who made the mistake, and the passive was hiding that.

Why grammar drills alone did not fix this, and what does

One honest paragraph. Graham and Perin (2007), in a meta-analysis of writing instruction for students in Grades 4 to 12, found traditional grammar instruction (the parts of speech, the rules, the drills) to be the one treatment with a negative average effect on the quality of students' writing, while sentence-combining practice, in which students join short sentences into longer ones, improved it. Hartwell (1985) had argued the same thing from the classroom twenty years earlier: knowing the rule and writing the sentence are different skills, and the first does not produce the second. The lesson is not that grammar does not matter. It is that the rule is learned in your own sentences, not in a worksheet.

What does work: the full-stop test on your own draft, read aloud, after the ideas are fixed. Sentence editing is Step 8 of the whole essay in order for a reason: a splice in a paragraph you are about to cut is not worth mending. Read the paragraph aloud and find the sentence that does not stop; that is chapter 4 of the free playbook. A grammar checker, as a category, flags a comma splice reliably, flags the passive whether or not it is the right choice, and cannot tell a deliberate fragment from a mistake; what essay checkers catch and miss says where to trust one. One more place a splice hides: the join where a quotation enters your sentence, The authors say this, "the gain lasted a week", which is a splice with quotation marks on it; the forms that integrate a quotation properly are in integrating a quotation into a sentence.

The four faults on one screen

The fault	The test	The repair
Comma splice	Two full stops would work where the comma is	A full stop, a semicolon, or a comma plus and, but, so, or, yet, for, nor
Run-on	Two complete thoughts with no joint	The same three
Fragment	A full stop after it leaves a question hanging	Attach it, or give it a subject and a finite verb
Hiding passive	By someone fits after the verb, and the actor matters	Put the actor first; keep the passive where the thing done is the topic

And the one word to watch: however. It joins by semicolon or full stop, never by comma alone.