Sentence boundaries and run-ons

The question always reads: “Which choice completes the text so that it conforms to the conventions of Standard English?” It never names the rule, so look at the choices. They keep the same words and change the mark, sometimes adding a small word such as “and” or “which.”

Run the test on this blank:

“After the bridge closed for repairs ______ most drivers switched to the ferry.”

1. Look back toward the start of the sentence. If a comma, dashA long mark used alone before an explanation or in pairs around an added detail., or parenthesis opened some extra words, the blank may close them with the same mark. Nothing opens here.
2. Read the words before the blank as if the sentence stopped there: “After the bridge closed for repairs.” That can’t stand alone, because “After” leaves you waiting.
3. Read the words after the blank as if a new sentence started there: “Most drivers switched to the ferry.” That could stand alone.
4. Match what you found:
   • If both sides could, use a period or a semicolon, or a comma plus “and,” “but,” or “so.” A comma alone is wrong, and so is no mark.
   • If the left side could and the right side explains or lists, use a colonThe mark : which follows a complete sentence and introduces what comes next. or one dash. Semicolons, colons, and dashes teaches those.
   • If the left side could and the right side is extra words that describe or comment on it, use a comma, as in “The layers form bands, which record each season.”
   • If the left side is only opening words, use a comma.
   • If the blank splits words that belong together, such as a subjectThe who or what a sentence is about. In “The vault held papers,” it’s the vault. and its verbA word for what something does or is, such as carry or seem., use no mark.
   • If the blank sits between list items that already contain commas, use a semicolon, as in “Reno, Nevada; Salem, Oregon; and Boise, Idaho.” A colon won’t work.

Here the left side is only opening words, so the blank takes a comma. A semicolon or period would cut off words that can’t stand alone.

Cross out “After” and both sides could stand alone. Now a comma alone is wrong, and a semicolon or a comma plus “and” works. One word changed the answer, so read every word a choice adds.

“These layers, which form bands ______ record each season.”

Step 1 takes you back to the comma after “layers.” Cross out “which form bands” and what’s left is still a full sentence with the same point. Those are extra words, the nonessentialA part you could cut and still have a complete sentence that makes sense, so it gets a mark on each side, such as two commas.Read the lesson part.

A side can stand alone when it has a subject and a verb with a time on it, such as “cooled,” “is,” or “was mapping.”

• “The kiln in the north yard, still warm from the last firing” has no such verb. Swap the comma for “was” and it stands alone.
• An “-ing” word or a “to” word can’t do the job alone. Add “was” and “The crew mapping the riverbed” becomes “The crew was mapping the riverbed.” “Ito to record every call” needs a verb such as “planned”: “Ito planned to record every call.”

Some words leave you waiting for the rest even when a side has a subject and a verb. Call them waiting words:

• “because,” “although,” “while,” “when,” “since,” “if,” “unless,” “after,” “before,” “whether,” “as,” “so that”
• “which,” “that,” “who,” “whose,” “where”

A waiting word affects only its own part. In “Although the flutes look identical, measurements reveal differences ______ analysis links those differences to their construction,” the “although” part ends at the comma after “identical.” The blank sits between two full sentences, so a comma alone is wrong.

A period or a semicolon can go between two full sentences. So can a comma plus one of the seven joining words: “and,” “but,” “or,” “so,” “yet,” “for,” “nor.” A colon or one dash also works when the second sentence explains the first. A period and a semicolon do the same job here, so if two choices differ only in that mark, neither can be the answer.

“However,” “therefore,” “instead,” and “for instance” link ideas but can’t join two full sentences. Each sits inside one sentence, with the break on its other side.

“The timetable promised uninterrupted service. The first six trips ran on schedule ______ the last two trips were canceled.”

• A. ; however,
• B. , however,
• C. , however;
• D. however,

Try “however” with each side. The first six trips kept the promise, so the contrast is the canceled trips, and “however” starts that second sentence, as in A. B joins full sentences with commas alone. C puts “however” with the wrong sentence, and D has no break.

With a comma after it, “though” works like “however,” so “The vents are narrow, though, the airflow is steady” is wrong. Without that comma, it means “although,” and “The vents are narrow, though the airflow is steady” is right.

A short phrase at the break goes with the side it makes sense on: “Each dolphin makes its own whistle; from recordings alone, researchers can tell the animals apart.” Dolphins don’t make whistles from recordings, so the break goes before the phrase.

After the full sentence, the same words usually take no comma: “Timetables grouped departures by hour as networks expanded.” The exception is a contrast. “Although,” “though,” “whereas,” and “while” meaning “whereas” take a comma even at the end: “The early ledgers list sacks, whereas the later ones list wagons.”

Openings with no subject work the same way: “Preserved by the salt, the timbers survived.”

When the blank splits words that belong together, choose no mark, no matter how long the sentence is.

No mark goes before “that” when the words after it say which ones: “The team kept only samples that contained quartz.”

Work the three examples, then try five more. Their explanations call a full sentence an independent clauseA clause that could stand on its own as a sentence. “The road reopened” is one..