University admissions preparation Grammar: Boundaries and Punctuation
In this lesson you will learn the foundation of the SAT Reading and Writing Standard English Conventions questions — the complete-sentence test, the rules for commas, semicolons, colons and dashes, and ways to fix run-ons and fragments — and then check your skills on 10 original practice questions.
7 min read · Updated 10/23/2026
Contents
Why Boundaries Matter: The Complete-Sentence Test
In the digital SAT's Reading and Writing section, Standard English Conventions questions make up roughly a quarter of the questions. The domain includes both Boundaries and Form, Structure, and Sense. This lesson focuses mainly on boundaries: telling an independent clause from a dependent one is important here, but does not by itself solve every grammar question.
The complete-sentence test. When checking an ordinary declarative sentence, read the part on its own and answer two questions: Who or what? (the subject) and What happens, or what is it? (a complete predicate). If both are there and the thought is finished, the part is independent:
The observatory opens at sunset.— subject + predicate, thought complete: independent.Because the observatory opens at sunset.— because makes the clause dependent; it is waiting for a result.Opening at sunset to greet visitors.— opening is not a finite verb, and there is no subject either.
Words such as because, although, when, if, since, while can introduce dependent clauses when used as subordinators; that, which, who can do so when used as relative pronouns. Check the word’s role: who/which can also be question words, and that can be demonstrative. Seeing one of these words does not always mean the part is dependent.
Comma, Semicolon, Colon and Dash: The Basics
In these sentence-boundary examples: *a period or semicolon can go between two complete sentences; a colon or emphatic single dash can come after a complete sentence to introduce an explanation, a list, or a quotation.* This is not every use of these marks: a semicolon can also separate complex list items that contain commas.
| Mark | Function | Example |
|---|---|---|
, + FANBOYS | joins two independent clauses | Rehearsal ended early, so the cast celebrated. |
; | joins two independent clauses without a conjunction | Rehearsal ended early; the cast celebrated anyway. |
: | after a complete sentence, introduces a list, an explanation, or a quotation | One rule mattered most: arrive on time. |
— | emphasis, like a colon; used as a pair, it sets off an interrupting phrase | One rule mattered most—arrive on time. |
Notes:
- FANBOYS = for, and, nor, but, or, yet, so. When these join two independent clauses, a comma normally precedes the conjunction; it may be omitted between very short, closely related clauses when clarity is maintained. Do not treat a bare comma as a standard repair without a conjunction.
- Conjunctive adverbs such as however, therefore are not FANBOYS; a plain comma is not enough with them:
The road was icy; therefore, we drove slowly. - The dash is versatile, but a pair that opens must close.
Run-ons and Fragments: Spotting the Classic Errors
A run-on comes in two forms: fused (no punctuation at all) and comma splice (only a comma). Both are the same error — two complete sentences joined illegally.
- Fused:
Glaciers store most of Earth's freshwater they feed rivers worldwide. - Splice:
Glaciers store most of Earth's freshwater, they feed rivers worldwide.
Five legitimate fixes:
- Period:
...freshwater. They feed... - Semicolon:
...freshwater; they feed... - Comma + FANBOYS:
...freshwater, and they feed... - Make one clause dependent:
Because glaciers store most of Earth's freshwater, they feed... - Conjunctive adverb:
...freshwater; moreover, they feed...
A fragment is the opposite problem: there is no subject or predicate, or a dependent clause is left standing alone. The classic trap is a long noun phrase that looks like a sentence: The report, drafted over months by experts. There is no predicate! Either add one (The report was drafted...) or attach the fragment to the complete sentence before it.
The Complete Rule Set: Boundaries and Punctuation
Model answers and detailed strategies are included with Pro access. Tests are purchased separately.
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