You decide how two stretches of text should be joined. The core skill is recognizing whether each side of the blank is an independent clause, meaning it has its own subject and verb and could stand alone. Two independent clauses need a period, a semicolon, or a comma plus a coordinating conjunction. A comma alone between them is a comma splice, and no punctuation at all is a run-on. Choices often include a transition word inserted with commas, which does not fix the join.
Standard English Conventions is about 26 percent of the 54 reading and writing questions, and sentence boundaries are usually around 2 to 4 of them.
Where students lose points
Joining two independent clauses with a comma plus a transition like however, which is still a comma splice.
Treating a clause that starts with although or because as independent, when the subordinator makes it dependent.
Choosing a semicolon when one side of the blank is not a complete sentence.
How to attack these questions
1Read the text on each side of the blank separately and ask whether each could stand alone as a sentence.
2If both sides are independent, cross out every choice that uses only a comma or no punctuation at all.
3If one side is dependent, look for the choice with a comma or with no punctuation, not a semicolon or a period.
Example questions
Written for this skill, with the answer explained. 117 more are in the app.
Try one
Sentence boundaries
Real question
While repairing a seawall in ______ engineers uncovered the timber frame of a fishing boat that had been buried in the fill.
Which choice completes the text so that it conforms to the conventions of Standard English?
The answer is C
"While repairing a seawall in 1998" is an introductory dependent element with no subject of its own, so it is set off from the main clause with a comma. Writing "1998;" requires an independent clause before the semicolon, and this phrase is not one. Writing "1998" runs the introductory phrase straight into the subject "engineers." Writing "1998. And" leaves the "While" phrase as a fragment and then opens a sentence with a conjunction that has nothing to coordinate.
Easier
The 1908 expedition across the plateau carried only what four mules could ______ a canvas tent, a theodolite, and six weeks of dried food.
Which choice completes the text so that it conforms to the conventions of Standard English?
A) haul: ✓
B) haul,
C) haul
D) haul;
Why: "The 1908 expedition across the plateau carried only what four mules could haul" is a complete clause, and the colon introduces the list that specifies what that was. Writing "haul," gives too weak a break to introduce the list, so the items read as loose appositives rather than as the specification of what was hauled. Writing "haul" supplies no punctuation and fuses the list onto the verb. Writing "haul;" calls for an independent clause after the semicolon, but "a canvas tent, a theodolite, and six weeks of dried food" has no verb.
Easier
Desalination plants separate salt from seawater at enormous energy ______ the brine left behind, twice as salty as the ocean, must then be diluted before it can be returned without harming the seabed.
Which choice completes the text so that it conforms to the conventions of Standard English?
A) cost, and,
B) cost and
C) cost and,
D) cost, and ✓
Why: "Desalination plants separate salt from seawater at enormous energy cost" and "the brine left behind must then be diluted" are both independent clauses, so "and" takes a comma before it and no comma after it. Writing "cost, and," adds a comma right after the conjunction, which treats "and" as an interrupter and separates it from the clause it introduces. Writing "cost and" leaves out the comma that a conjunction joining two independent clauses requires. Writing "cost and," makes both mistakes at once, no comma before the conjunction and a stray one after it.
Harder
Restoration crews on remote islands plan around the boat rather than the weather, because a missed sailing costs more than a week of rain. Because the ferry to the island runs only twice a ______ the crew of the lighthouse restoration project, which has grown substantially since its founding, plans its supply orders a month ahead.
Because the ferry to the island runs only twice a ______ the crew of the lighthouse restoration project, which has grown substantially since its founding, plans its supply orders a month ahead.
A) week, the ✓
B) week, and the
C) week the
D) week; the
Why: 'Because the ferry to the island runs only twice a week' is a dependent clause, and a comma hands it off to the main clause 'the crew ... plans its supply orders a month ahead': 'week, the'. 'week the' omits that comma, so the dependent clause runs straight into the subject. 'week; the' uses a semicolon, which requires an independent clause before it, and the 'Because' clause is not one. 'week, and the' adds 'and', which would coordinate two elements of equal rank, but a dependent clause and an independent clause cannot be coordinated that way.
Questions students ask
What is a comma splice?
It is two independent clauses joined by only a comma, such as the lab opened at nine, the results arrived by noon. To fix it you need a period, a semicolon, or a comma plus a conjunction like and, but, or so. Adding however after the comma does not fix it.
When should I use a semicolon instead of a comma?
Use a semicolon when both sides are complete sentences and there is no coordinating conjunction joining them. If either side cannot stand alone, a semicolon is wrong. A semicolon works anywhere a period would work.
How do I tell if a clause is independent?
Check that it has a subject and a working verb and does not start with a subordinator such as because, although, when, or since. If a word like although opens the clause, it is dependent no matter how long it is.
Drill this skill until it is automatic
Questions on sentence boundaries alone, with explanations on every one, and the app tracks which ones you keep missing.