Digital SAT · Guides · November 6, 2026 · 7 min read
SAT grammar rules: the punctuation and sentence rules behind most Standard English Conventions questions
Standard English Conventions is the grammar domain of the Digital SAT Reading and Writing section, about 26% of its questions, or roughly seven per module. Each question shows a short passage with a blank and four options that differ only in punctuation or in the form of a word. The good news is that the test returns to the same small set of rules again and again. If you learn the rules below and the habit of checking what sits on each side of the blank, these become the fastest points in the section: 30–45 seconds a question.
The domain has two skills. Boundaries is punctuation: how clauses and phrases are joined or separated. Form, Structure, and Sense is everything else: agreement, verb forms and tenses, pronouns, plurals and possessives, and modifiers. In each module the questions from both skills are mixed together, after the reading questions and before Transitions and Rhetorical Synthesis.
The first step for every Boundaries question
Before looking at the punctuation, decide what is on each side of the blank:
- An independent clause has a subject and a finite verb and could stand alone as a sentence: The museum reopened in May.
- A dependent clause or phrase cannot: when the museum reopened, after years of repairs, built in 1902.
Most Boundaries questions are answered by this one check.
Boundaries: the rules
1. Joining two independent clauses. You have four correct options:
| Pattern | Example |
|---|---|
| Period | The trail was closed. Hikers took the river path. |
| Semicolon | The trail was closed; hikers took the river path. |
| Comma + and, but, or, so, yet, for, nor | The trail was closed, so hikers took the river path. |
| Colon (when the second clause explains the first) | The trail was closed for one reason: a bridge had collapsed. |
A comma alone between two independent clauses is a comma splice, and nothing at all is a run-on. Both are always wrong on the SAT.
2. A semicolon needs a complete sentence on both sides. The only exception is a list whose items already contain commas: Paris, France; Lagos, Nigeria; and Lima, Peru.
3. A colon or a single dash needs a complete sentence before it. What follows can be a list, a word, a phrase or a clause that explains or illustrates what came before. “The kit included: a map” is wrong; “The kit included one essential item: a map” is right.
4. No punctuation between core sentence parts. Never separate a subject from its verb, a verb from its object, or a preposition from its object, even when the subject is long. “The rare orchids that grow on the island’s northern cliffs, bloom only in March” is wrong; delete the comma.
5. Nonessential information takes a matching pair. An extra phrase that can be lifted out without changing the core meaning is set off by two commas, two dashes or two parentheses. You cannot open with a dash and close with a comma. If the blank is at the end of such a phrase, look back for how it started.
6. Essential information takes no commas. Titles and descriptions directly before a name do not get commas: the chemist Marie Curie, the novel Beloved. A restrictive that clause never takes commas either.
7. Conjunctive adverbs are not conjunctions. However, therefore, moreover, consequently, nevertheless cannot join two clauses with only commas. When they begin the second clause, use a semicolon or period before them and a comma after: The forecast was poor; however, the launch went ahead.
8. Apostrophes mark possession, not plurals. The scientists’ results (several scientists), the scientist’s results (one). Its is possessive; it’s means it is. The same for their / they’re and whose / who’s.
Form, Structure, and Sense: the rules
1. Subject–verb agreement. Find the real subject and ignore what comes between it and the verb, especially prepositional phrases: The list of recommended books is long. Words like each, every, either and collective nouns such as team, committee, collection usually take a singular verb.
2. Pronoun agreement. A singular noun takes it or its; a plural noun takes they or their. Companies, agencies and teams are singular: The agency released its report, not their report.
3. Verb tense follows the timeline. Keep the tense consistent with the rest of the passage unless the time actually changes. Use the past perfect (had found) for an action that happened before another past action.
4. A sentence needs a finite verb. If the subject is followed only by -ing forms or to + verb, the sentence is incomplete: “The researchers, working in the field for months, discovered” is complete; “…, discovering” is not.
5. Modifiers must touch what they describe. An introductory phrase such as “Born in Lisbon,” or “Trained as an engineer,” describes the noun that comes right after the comma. If that noun is not the person or thing described, the modifier is dangling.
6. Plural and possessive nouns. Decide first whether the word owns the noun after it; if it does not, there is no apostrophe.
Three worked examples
These are original questions written for this guide, not official SAT questions.
Example 1: Boundaries
In 1928 the bacteriologist Alexander Fleming noticed that a mold growing on one of his culture plates had killed the bacteria around ______ the substance the mold produced, later named penicillin, transformed the treatment of bacterial infections.
Which choice completes the text so that it conforms to the conventions of Standard English?
A) it,
B) it;
C) it
D) it, however,
Answer: B. Check both sides: “In 1928 … killed the bacteria around it” is an independent clause, and so is “the substance … transformed the treatment of bacterial infections”. Two independent clauses with no conjunction need a semicolon (or a period). A is a comma splice and C is a run-on. D is still a comma splice: however is a conjunctive adverb, not a conjunction, and it also adds a contrast the passage does not have. Note that “the bacteriologist Alexander Fleming” correctly has no commas (rule 6).
Example 2: Subject–verb agreement
The collection of letters written by the expedition’s crew members during the long Antarctic winter ______ now kept in a climate-controlled archive in Hobart, Tasmania.
Which choice completes the text so that it conforms to the conventions of Standard English?
A) are
B) is
C) were
D) have been
Answer: B. Strip the sentence down: “The collection … is now kept.” Letters, members and winter all sit inside modifying phrases; the subject is collection, which is singular, and now calls for the present tense. A, C and D are plural, which is the trap: the plural noun crew members stands right before the blank.
Example 3: Modifier placement
Trained as a chemist before she turned to painting, ______
Which choice completes the text so that it conforms to the conventions of Standard English?
A) the pigments in Rosa Iturbe’s canvases were often mixed by hand from minerals she collected herself.
B) Rosa Iturbe often mixed the pigments for her canvases by hand from minerals she collected herself.
C) mixing pigments by hand from minerals she collected herself was Rosa Iturbe’s habit.
D) Rosa Iturbe’s canvases often featured pigments she mixed by hand from minerals she collected herself.
Answer: B. Ask who was trained as a chemist: the painter. So the words right after the comma must be Rosa Iturbe. A puts the pigments there, C puts mixing, and D puts Rosa Iturbe’s canvases. D is the cleverest trap because her name appears first, but the possessive makes canvases the subject, and canvases were not trained as chemists.
Common mistakes
- Choosing by ear. A comma “where you would pause” is not a rule, and long sentences on the SAT are designed to sound like they need one.
- Forgetting the start of the sentence. When the blank closes a nonessential phrase, the answer depends on how that phrase opened.
- Treating however like but. It needs a semicolon or a period before it when it starts a new clause.
- Agreeing with the nearest noun. Always find the real subject.
- Picking the longest or most formal option. Wordier is not more correct, and only one option in a conventions question is grammatical, so a short, plain choice is often the right one.
How to practice
Learn the rules in two passes: first Boundaries, then Form, Structure, and Sense, ten to fifteen questions at a time, reading the explanation of each one. In Nomto you can drill Boundaries and Form, Structure, and Sense separately, then mix them in the Standard English Conventions set to match the test, where the two skills are interleaved. Keep a list of the rule behind every mistake; after a few sessions it usually shrinks to two or three rules you need to watch. For where these questions sit among the others and how to budget time across the module, see the SAT Reading and Writing guide; the transition questions that follow them are covered in SAT Transitions and Rhetorical Synthesis.