American Diploma · Digital SAT · Standard English Conventions

Sentence Boundaries

Find the clauses, test them, and choose the one correct way to join or separate them — comma splices, run-ons, fragments and “however” traps, with 12 practice questions.

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What this question type tests

Sentence boundaries belong to the Standard English Conventions domain of the Digital SAT Reading and Writing section. This domain is about 26% of the scored questions (11–15 questions across the two modules). The College Board calls the punctuation skill Boundaries: it covers punctuation at the end of a sentence and inside a sentence — linking clauses, separating list items, setting off extra information, and knowing when no punctuation is needed. This page teaches the first and most important part: where one sentence ends and the next one begins.

On the test you see one short passage (25–150 words) with a blank, like this: “The museum closed at noon ______ the staff began preparing the new exhibit.” The question underneath says: “Which choice completes the text so that it conforms to the conventions of Standard English?” The four choices look almost the same — the same words with different punctuation (a comma, a semicolon, a period, nothing). Only one choice gives a correct sentence. These questions usually appear in the second half of each module, after the reading questions.

The good news: boundary questions follow a small set of fixed rules. If you learn to find the clauses and to test whether each one is independent, you can answer almost every one in under a minute — which matters, because you have about 1 minute 11 seconds per question.

الفكرة الأساسية

قبل ما تختار أي علامة ترقيم، اسأل نفسك: الجزء اللي قبل الفراغ جملة كاملة ولا لأ؟ والجزء اللي بعده جملة كاملة ولا لأ؟ لو الاتنين جمل كاملة، يبقى محتاج نقطة أو فاصلة منقوطة (;) أو فاصلة + and/but/so… — الفاصلة لوحدها غلط.

Step 1: Independent vs dependent clauses

A clause is a group of words with a subject and a verb. There are two kinds:

Type	What it is	Example
Independent clause	Subject + finite verb + a complete thought. It can stand alone as a sentence.	The river flooded the valley.
Dependent clause	Has a subject and verb, but starts with a word that makes it incomplete. It cannot stand alone.	Because the river flooded the valley …

Words that make a clause dependent (subordinating words): although, because, since, when, while, if, unless, until, after, before, whereas, even though, as soon as, so that — and the relative words which, who, whom, whose, that (when they start a describing clause).

How to test a clause — three quick tests:

The stand-alone test. Cover everything else. Read the clause alone with a period at the end. Does it sound like a complete statement? “The river flooded the valley.” ✓ Complete. “Because the river flooded the valley.” ✗ The listener waits for more.
The finite-verb test. Find the main verb. Words ending in -ing (flooding), to + verb (to flood) or a past participle on its own (flooded by rain) are NOT finite verbs. “The river flooding the valley.” ✗ No finite verb, so not a sentence.
The “I realized that …” test. Put “I realized that” in front of the clause. If the result makes sense, the clause is independent. “I realized that the river flooded the valley” ✓. “I realized that because the river flooded the valley” ✗ — so the “because” clause is dependent.

Find the clauses first

Before you look at the choices, read the full text and mark the two halves around the blank. Ask: “Left side complete? Right side complete?” Your answers to these two questions decide the punctuation almost every time.

Step 2: The 4 correct ways to join two independent clauses

When BOTH sides are independent clauses, you have exactly four correct options. Learn this table — it is the heart of the whole topic.

#	Method	Pattern	Example
1	Period	Independent. Independent.	The bridge was finished in 2010. It carries 50,000 cars a day.
2	Semicolon	Independent; independent.	The bridge was finished in 2010; it carries 50,000 cars a day.
3	Comma + FANBOYS	Independent, and/but/so/or/yet/for/nor independent.	The bridge was finished in 2010, and it carries 50,000 cars a day.
4	Colon (only when the second clause explains the first)	Independent: independent that explains it.	The bridge was a success: it carried 50,000 cars a day in its first year.

FANBOYS = for, and, nor, but, or, yet, so. These are the coordinating conjunctions. Only these seven can join two independent clauses with a comma.

The semicolon's job (the teacher's rule): a semicolon joins two independent clauses that are closely related. Both sides must be complete sentences — think of a semicolon as a “soft period.” If you could not put a period there, you cannot put a semicolon there.

The colon's job: a colon comes after a complete sentence and introduces a list, an explanation, emphasis or extra information. When you use it to join two clauses, the second clause must explain or expand the first.

✓ The bakery's ovens broke down on Friday; the owners gave away free coffee instead of bread.
✓ The bakery's ovens broke down on Friday, so the owners gave away free coffee instead of bread.
✓ The owners had a simple plan: they would give away free coffee until the ovens were fixed. (the second part explains the plan)
✗ The bakery's ovens broke down on Friday, the owners gave away free coffee instead of bread. (comma splice)
✗ The bakery's ovens broke down on Friday the owners gave away free coffee instead of bread. (run-on)
✗ The bakery's ovens broke down on Friday; so the owners gave away free coffee. (semicolon + FANBOYS — use a comma before “so” instead)

Period = semicolon on the SAT

Between two independent clauses, a period and a semicolon are grammatically equal. So the test will never offer both as the only difference between two choices — that would give two correct answers. If you see “. The” and “; the” both looking right, look again: one of them must have a different problem somewhere else.

Step 3: The three big errors

Error 1: The comma splice

A comma splice is two independent clauses joined with only a comma. It is the single most common wrong answer in boundary questions.

✗ Camels can drink 100 liters of water in a few minutes, they store energy as fat in their humps.
✓ Camels can drink 100 liters of water in a few minutes; they store energy as fat in their humps.
✓ Camels can drink 100 liters of water in a few minutes. They store energy as fat in their humps.

Watch out for pronouns. A second clause that starts with it, they, this, these, she, he, which is often the clue. “This,” “it” and “they” start independent clauses; “which” starts a dependent clause.

✗ The team finished the survey early, this gave them time to check the data.
✓ The team finished the survey early, which gave them time to check the data. (which-clause = dependent, so a comma is fine)

Error 2: The run-on (fused sentence)

A run-on is two independent clauses with no punctuation and no joining word between them.

✗ The library opens at nine on weekdays it opens at ten on Saturdays.
✓ The library opens at nine on weekdays, but it opens at ten on Saturdays.

Error 3: The fragment

A fragment is a group of words punctuated as a sentence (capital letter + period) that is not a complete sentence. Common causes:

A dependent clause alone: ✗ Although the results were surprising. ✓ Although the results were surprising, the team repeated the test.
No finite verb: ✗ The new stadium, holding more than 70,000 fans. ✓ The new stadium holds more than 70,000 fans.
A period that cuts off a which-clause: ✗ The plan saved money. Which pleased the board. ✓ The plan saved money, which pleased the board.
A subject + extra information but no main verb: ✗ The researcher, who had studied the desert for ten years and knew every path. ✓ The researcher, who had studied the desert for ten years, knew every path.

The long-subject trick

When a sentence has a long subject with extra information between commas, cross out the extra information. In “The Rosetta Stone, discovered in 1799, gave scholars …” cross out “discovered in 1799.” Now you can see the subject (Rosetta Stone) and check that it has a real verb (gave).

Dependent + independent: how to punctuate

Pattern	Punctuation	Example
Dependent clause first, then independent	Comma after the dependent clause	When the storm ended, the fishermen returned to the harbor.
Independent first, then a dependent clause (because, when, if, after…)	Usually no comma	The fishermen returned to the harbor when the storm ended.
Independent, then a non-essential which-clause	Comma before which	The storm ended at dawn, which surprised the forecasters.
Dependent clause + semicolon	✗ Never	✗ When the storm ended; the fishermen returned.

Conjunctive adverbs: however, therefore, as a result …

Words like however, therefore, consequently, moreover, furthermore, nevertheless, meanwhile, thus, instead, otherwise, as a result, in fact, for example, in addition are NOT FANBOYS. They show a logical link, but they cannot join two independent clauses with a comma. When one of them starts the second independent clause, put a semicolon or a period before it and (usually) a comma after it.

✗ The road was closed, however, the bus found another route. (comma splice)
✓ The road was closed; however, the bus found another route.
✓ The road was closed. However, the bus found another route.
✓ The road was closed, but the bus found another route. (FANBOYS — comma is enough)

But — when the adverb sits in the middle of ONE clause, it is just extra information and takes a pair of commas:

✓ The bus, however, found another route. (one clause only: “The bus found another route.”)
✗ The bus; however, found another route. (the left side “The bus” is not a clause)

How to decide: look at what comes before and after “however.” If there is a complete sentence on BOTH sides, you need “; however,” or “. However,”. If “however” interrupts a single sentence, use “, however,”.

however وأخواتها

كلمات زي however / therefore / as a result مش زي and و but. لو قبلها جملة كاملة وبعدها جملة كاملة، لازم قبلها ; أو نقطة، وبعدها فاصلة: ; however, — أما لو جت في نص جملة واحدة يبقى بين فاصلتين: , however,

Question marks: direct questions only

Use a question mark only for a direct question — the actual words someone asks. An indirect question reports a question inside a statement, so it ends with a period. Words like “asked whether,” “wondered why,” “wanted to know how” are the clue.

✓ Why do some birds migrate at night? (direct question)
✓ The scientist asked why some birds migrate at night. (indirect — it is a statement)
✗ The scientist asked why some birds migrate at night?
✓ The question is simple: why do some birds migrate at night? (the direct question comes after the colon)

Worked examples

Worked example 1 — comma splice

Text: Sea turtles spend most of their lives far out in the ocean. Years later, many females return to the same beach where they hatched to lay their own eggs ______ scientists believe the turtles use Earth's magnetic field to find it.

Which choice completes the text so that it conforms to the conventions of Standard English?

A) eggs, scientists
B) eggs; scientists
C) eggs scientists
D) eggs, and, scientists

Answer: B

A) ✗ Wrong: Both sides are independent clauses (“many females return …” / “scientists believe …”). A comma alone between them is a comma splice.
B) ✓ Correct: A semicolon correctly joins two closely related independent clauses.
C) ✗ Wrong: No punctuation at all between two independent clauses is a run-on.
D) ✗ Wrong: Comma + “and” would be correct, but the extra comma after “and” is wrong — never put a comma straight after a FANBOYS word here.

Worked example 2 — conjunctive adverb

Text: A small team of students built a phone app that helps visitors find their way around a large hospital. The first version of the app was slow and confusing ______ the developers rebuilt it from scratch before releasing it to the public.

Which choice completes the text so that it conforms to the conventions of Standard English?

A) , consequently,
B) ; consequently,
C) , consequently
D) consequently

Answer: B

A) ✗ Wrong: “Consequently” is not a FANBOYS word, so a comma before it creates a comma splice.
B) ✓ Correct: Two independent clauses with a conjunctive adverb: semicolon before it, comma after it. Correct.
C) ✗ Wrong: Same comma-splice problem as A, and it also drops the comma after the adverb.
D) ✗ Wrong: No punctuation before “consequently” fuses the two clauses into a run-on.

Worked example 3 — fragment (missing finite verb)

Text: Egypt's rulers wanted to protect farms from both floods and droughts. The Aswan High Dam, completed in 1970 ______ the yearly flooding of the Nile and stores water in Lake Nasser for dry years.

Which choice completes the text so that it conforms to the conventions of Standard English?

A) 1970, controls
B) 1970, controlling
C) 1970 controls
D) 1970, which controls

Answer: A

A) ✓ Correct: “Completed in 1970” is extra information between a pair of commas. Removing it leaves “The Aswan High Dam controls … and stores …” — a complete sentence with a finite verb.
B) ✗ Wrong: “Controlling” is an -ing form, not a finite verb. The sentence would have no main verb (fragment) — and “and stores” would have nothing to match.
C) ✗ Wrong: The opening comma after “Dam” needs a matching closing comma after “1970.”
D) ✗ Wrong: “Which controls” turns the rest into a dependent clause, so the subject “The Aswan High Dam” never gets a main verb: fragment.

Worked example 4 — colon for an explanation

Text: Wildlife researcher Omar Saleh spent two summers following a family of desert foxes. He noticed something unusual about the foxes he studied ______ they were active during the hottest hours of the day, when their prey was easiest to catch.

Which choice completes the text so that it conforms to the conventions of Standard English?

A) studied, they
B) studied: they
C) studied they
D) studied, so that they

Answer: B

A) ✗ Wrong: Two independent clauses joined by a comma only: comma splice.
B) ✓ Correct: The first clause is complete and says he noticed “something unusual”; the second clause explains what it was. This is exactly the colon's job.
C) ✗ Wrong: No punctuation between two independent clauses: run-on.
D) ✗ Wrong: “So that” means “in order that” (purpose). The foxes were not active in order that he noticed them, so the meaning is illogical.

Classic traps

The comma splice in disguise: the second clause begins with “it,” “this,” “they” or a name. A comma alone is never enough.
“However” with commas only: “…, however, …” between two complete sentences is a comma splice.
Semicolon before a dependent clause: “; because,” “; which,” “; although” — the right side is not complete, so the semicolon is wrong.
Semicolon + FANBOYS: “; and” or “; but” between two simple clauses — use a comma instead.
The broken pair of commas: the subject is followed by extra information that opens with a comma but never closes it, so the verb looks separated or missing.
The -ing fragment: an answer that changes the main verb to an -ing form (“controlling,” “being”) leaves the sentence without a finite verb.
The indirect question with “?”: “asked whether …?” — a reported question ends with a period.

Fast strategy for test day

Read the whole text, then look at the choices: if only the punctuation changes, it is a boundary question.
Split the sentence at the blank. Test the left side and the right side: complete or not?
Both complete → you need a period, a semicolon, comma + FANBOYS, or a colon (if the second explains the first). Cross out every choice with a comma alone or nothing.
One side incomplete → no semicolon and no period; usually a comma or nothing.
If two choices seem equal (“.” vs “;”), find the other difference — the test never has two correct answers.
Do not spend more than about one minute; these are the questions where you can save time for harder reading items.

Practice

Twelve original questions in SAT format. Take your time, then read every explanation — including for the questions you got right.

Remember

Test both sides of the blank: is each one an independent clause (subject + finite verb + complete thought)?
Two independent clauses: period, semicolon, comma + FANBOYS, or a colon if the second explains the first. Never a comma alone, never nothing.
however / therefore / as a result between two sentences: “; however,” or “. However,” — inside one sentence: “, however,”.
A dependent clause cannot stand alone and cannot sit next to a semicolon.
Question mark for direct questions only; “asked whether …” ends with a period.

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