Boundaries 1: complete sentences, run-ons and semicolons
Standard English Conventions is about 26% of Reading and Writing (11–15 of 54 questions), and boundary questions are among the most common. In each one the four choices differ only in punctuation, so you must know the rules, not just “how it sounds”.
What is a complete sentence?
A complete sentence has a subject (who or what), a verb (what it does) and expresses a complete thought. “The ferry leaves at six.” is complete. “Because the ferry leaves at six.” is not, even though it has a subject and a verb, because the word “because” makes it depend on another clause. Words such as because, although, when, if, since, while, after, before, which and who begin dependent clauses. A dependent clause alone is a fragment.
| Type | Example | Can stand alone? |
|---|---|---|
| Independent clause | The ferry leaves at six. | Yes |
| Dependent clause | Because the ferry leaves at six | No (fragment) |
| Fragment (no verb) | The old ferry in the bay. | No |
| Fragment (-ing only) | Leaving the port at six. | No |
Five ways to join two independent clauses
Two complete sentences may be joined or separated in only these ways. 1) A period: “It rained. We stayed home.” 2) A semicolon: “It rained; we stayed home.” 3) A comma plus a FANBOYS word: “It rained, so we stayed home.” 4) A colon, when the second clause explains the first: “We stayed home: it rained all day.” 5) Make one clause dependent: “Because it rained, we stayed home.” A comma alone cannot join two independent clauses. That mistake is called a comma splice.
| Tool | Pattern | Example |
|---|---|---|
| Period | Independent. Independent. | It rained. We stayed in. |
| Semicolon | Independent; independent | It rained; we stayed in. |
| Comma + FANBOYS | Independent, and independent | It rained, so we stayed in. |
| Colon | Independent: explanation | We stayed in: it rained. |
| Dependent clause | Because it rained, independent | Because it rained, we stayed in. |
The semicolon test
A semicolon works like a period: it needs a complete sentence on both sides. Cover the semicolon and ask: could the left part and the right part each stand alone? If yes, the semicolon is correct. If one side is a fragment (for example it starts with “although” or “which”), the semicolon is wrong. Never put a semicolon and “and” together before a clause: use one or the other.
Words like “however” and “therefore”
Words such as however, therefore, moreover, and instead are not joining words. They cannot connect two sentences with a comma. Use a semicolon before them and a comma after them: “The test was long; however, most students finished.” With a comma alone you would make a comma splice.
Fixing a fragment
A fragment is a piece of a sentence. To fix it, add the missing subject or verb, or connect it to the sentence next to it. Dependent clauses are usually joined to a nearby independent clause: “We waited at the station until the train arrived.” An introductory dependent clause is followed by a comma: “When the train arrived, we boarded.”
No punctuation needed
Do not add punctuation where the sentence does not need it. A comma before “and” is only required when “and” joins two complete sentences. “The students cleaned the yard and painted the fence” has one subject and two verbs, so it needs no comma. A colon or semicolon in the middle of a single clause is always wrong.
Farid packed his bag the night before the trip ______ checked the train times twice. In the morning he left home early and arrived with plenty of time to spare.
- Left of the blank: “Farid packed his bag the night before the trip” is a complete sentence.
- Right: “he checked the train times twice” is also complete.
- Two sentences need a period, a semicolon, or a comma plus a FANBOYS word.
- Only C offers a legal tool. A is a comma splice, B is a run-on, D mixes a semicolon with “and”.
The sky had been cloudy all morning ______ match began on time. By noon, the sun had come out, and the players were delighted with the dry field.
- Both sides of the blank are complete sentences.
- “However” is not a FANBOYS word, so a comma before it makes a comma splice (A and D).
- The pattern is semicolon, however, comma.
- B misses the comma after “however”. C is correct.
The guide stopped at the edge of the canyon ______ to a thin path far below. She warned the group to walk in single file and to keep away from the loose stones.
- “The guide stopped at the edge of the canyon” is a complete sentence.
- “Pointing to a thin path far below” has no subject of its own, so it is a fragment.
- A period (C) or a semicolon (A) would leave a fragment, and a colon (D) also needs a complete sentence before it and an explanation after it.
- A comma attaches the phrase to the sentence it describes.
In the kitchen of the small teahouse, the cook washed the rice ______ a pinch of salt to the pot. Then she covered it and waited for the water to boil, listening to the radio.
- Read each choice into the sentence: “the cook washed the rice and added a pinch of salt to the pot”.
- The sentence has one subject (the cook) and two verbs (washed, added).
- Words after “and” are not a complete sentence, so no comma is needed.
- A adds a comma that is only correct before a complete sentence; B and D create fragments.
- Joining two sentences with a comma aloneA comma splice is always wrong. Use a period, a semicolon, or a comma with a FANBOYS word.
- Putting a semicolon before a fragmentCover the semicolon. Both halves must be able to stand alone. A part that starts with “although”, “which” or “because” cannot.
- Adding a comma before every “and”Use a comma before “and” only if a complete sentence follows it. With two verbs for one subject, use no comma.
- Treating however as a joining wordWrite “; however,”. A comma alone before “however” is a comma splice.
- Choosing the period when the second part is a fragmentCheck that the words after the period form a complete sentence. If not, join them to the first sentence.
- Going by how the sentence soundsReading aloud pauses at commas, so a splice can sound fine. Test each side for a subject and a verb instead.