Grammar & punctuation rules reference

This is the lookup sheet for every grammar and punctuation rule tested on the SAT Reading & Writing section and the ACT English section. The two tests draw from the same finite set of rules — a comma splice is wrong on both — so the rules below apply to both unless marked ACT only. Each rule has one correct (✓) and one incorrect (✗) example. Rules tagged seen on real tests are ones whose answer pattern was confirmed against official released SAT/ACT items.

SAT & ACT Prerequisite · Writing · Reference

Punctuation

A period and a semicolon are grammatically identical on both tests — both join two complete sentences. Because they're identical, the test will never make you choose between them. A semicolon also goes before a conjunctive adverb (however, therefore, moreover) starting a new clause.

Boundary trap: read all the way to the period — one sentence can run on past where you'd expect, hiding a second complete sentence that needs stronger punctuation.

A colon or a single dash introduces a list or explanation, and must follow a complete sentence. Colons and dashes are interchangeable for this, so you won't choose between them. On the digital SAT, the colon is often the correct answer when two sentences must be joined and no period/semicolon option appears.

A comma plus a coordinating conjunction (For, And, Nor, But, Or, Yet, So) joins two complete sentences — equivalent to a period. But a comma + FANBOYS is wrong when the second part isn't a complete sentence (no new subject).

Shortcut: comma + and/but = period. Plug in a period; if you get a fragment, drop the comma.

A dependent clause starts with a subordinator (although, because, when, while, since, if, after) and can't stand alone. When it comes first, follow it with a comma; when it comes second, usually no comma. Never a semicolon between a dependent and independent clause.

Meaning & modifiers

Transition questions are about meaning, not grammar — all choices are grammatically fine, and you pick the one with the right logic. Three families: continuers (in addition, moreover, for example, then), cause-effect (therefore, thus, consequently), contradictors (however, nevertheless, in contrast).

Method: cover the transition, state the relationship between the two sentences (same / opposite / cause-effect) in your own words, then match. If two choices mean the same thing, both are wrong. ACT only If an OMIT/DELETE option exists, check it first — it's often correct.

Removable extra information is set off by a matched pair: two commas, two dashes, or two parentheses. Never mix the pair and never drop one half. If the phrase can be lifted out and the sentence still works, it's nonessential.

Single interrupting words like however take two commas (never two dashes): It does, however, have modern parts.

Only two correct options: no commas (the name is essential) or two commas (nonessential). A single comma before a name in mid-sentence is always wrong. Test by removing the name.

Commas should not appear: between a subject and its verb (even a long subject); before/after a preposition; between two items joined by and; or around the word that.

On a real SAT item, the correct answer was simply "no punctuation," because every other choice inserted a needless mark between a long subject and its verb. Take "no punctuation" choices seriously.

Words & agreement

Nouns: apostrophe = possessive (singular cell's, plural cells'); no apostrophe = plain plural. Pronouns are the opposite: possessive pronouns take no apostrophe.

• its = possessive; it's = "it is"; its' doesn't exist.
• their = possessive; they're = "they are"; there = place.
• whose = possessive; who's = "who is."

Tip: when it's/its is tested, its is the answer more often, because students over-associate apostrophes with possession. Confirmed on a real ACT item (its usage).

Who(m) for people, which for things, that for either. Who = subject; whom = object (after a preposition, or where "him/them" would fit). A pronoun must also agree in number with the noun it replaces.

Match the verb to its true subject in number. The test buries the subject behind prepositional phrases or nonessential clauses — strip those out. Two singular subjects joined by and are plural; each and every are singular.

Keep tense consistent with the surrounding sentences. A main clause needs a finite verb (one that shows tense, like claim/claimed) — a participle (claiming, having claimed, to claim) can't be the main verb. Use have/has + verb with for/since; use had + verb with by the time.

Watch: "tense" questions are often agreement questions in disguise — if the choices differ in both tense and number, the number usually decides it. Complex tenses (would have done) are almost always wrong.

Items in a list or comparison must share the same form. Fixed word pairs must stay paired and parallel: neither…nor, not only…but also, as…as, more/less…than.

When a sentence opens with a descriptive phrase + comma, the noun right after the comma must be the thing that phrase describes. Otherwise it dangles.

Confirmed on a real SAT item: the answer placed the modified noun immediately after a "Based on events…" opening; every distractor created a dangler.

Compare like with like — things to things, people to people. The phrases that of (singular) and those of (plural), or a possessive, fix mismatched comparisons.

ACT only Use than (not then) for comparisons. Quantity words: number/many/fewer for countable plurals, amount/much/less for singulars.

Rarely tested. Use a question mark only for a direct question. An indirect question embedded in a statement takes a period.

ACT only  Rules specific to the ACT English section

These appear on the ACT but not the digital SAT. The SAT tests rhetoric differently (under Expression of Ideas), so treat this block as ACT-specific.

When several choices are grammatically correct and say the same thing, the shortest one is almost always right. The ACT penalizes wordiness and redundancy.

You can often pre-pick the shortest choice on sight, then verify it isn't missing needed information.

Adjectives modify nouns; adverbs (usually -ly) modify verbs. Don't double up comparatives/superlatives (more + -er or most + -est is wrong).

Tested in compounds (name + pronoun or two pronouns). Cross out the other element and judge by ear. Between always takes object pronouns (me, him, them).

Pick the word that fits meaning and the idiomatic preposition; these go by ear. Two reliable rules: have, never of (could have, not could of), and register should be neither too formal nor too casual.