ACT Conventions of Standard English: Grammar Rules That Score Fast

Conventions of Standard English is the biggest of the three English domains, and unlike the other two, it's almost entirely rule-based. There's no judgment call about tone or organization here, just a rule you either know or don't. That makes it the fastest domain to get right once you've learned the handful of rules that repeat constantly.

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Did you know

Because this domain is rule-based rather than judgment-based, it's the one place on the whole ACT where memorizing a short list pays off almost immediately. Most students see faster score gains here than anywhere else in English.

What's tested

Four rule families show up constantly. Each one below has the quick version, plus a "Learn more" with the specific traps.

Comma usage

The single most tested rule family in this domain. Commas around extra information, commas in lists, and commas that don't belong.

Learn more: the pair rule and the unnecessary-comma trap

Nonessential information gets commas on both sides, or neither. If you can remove the phrase and the sentence still makes sense, it needs a comma before and after it, never just one.
Essential information gets no commas at all. "My sister who lives in Denver called" (no commas) means you have multiple sisters and this specifies which one. Adding commas would (wrongly) imply you have only one sister.
Never separate a subject from its verb with a single comma. "The players on the team, were tired" is wrong even though a pause feels natural there when you read it aloud.
Test every comma by covering it up. If removing it doesn't break the sentence's meaning and there's no clear rule requiring it, it's often the unnecessary-comma trap answer.

Apostrophes and possessives

Its versus it's, singular versus plural possessives, and when an apostrophe doesn't belong at all.

Learn more: the its/it's trap and where the apostrophe actually goes

"It's" always means "it is" or "it has." If you can't substitute one of those into the sentence, it should be "its" with no apostrophe. This single rule accounts for a large share of apostrophe questions.
Singular possessive: add 's. "The student's book" (one student). Plural possessive: add s' after the s. "The students' books" (multiple students). Read the sentence for how many owners there actually are before picking.
Plain plurals never get an apostrophe. "Three dogs" is correct; "three dog's" is a trap, plural does not mean possessive.

Subject-verb and pronoun-antecedent agreement

Making the verb match its real subject, and making a pronoun match what it refers to, even when other words sit in between.

Learn more: finding the real subject when words get in the way

Cross out prepositional phrases to find the real subject. "The box of crayons is on the table," not "are," the subject is "box," singular, not "crayons."
Collective nouns like "team" and "group" are usually singular on the ACT. "The team is ready," not "are."
A pronoun has to match its antecedent in number. "Each student must bring their own laptop" is a common real-world usage the ACT still tests as wrong in its formal grammar convention, "his or her" or a rewritten plural subject is the traditionally tested fix.
When a sentence has two subjects joined by "or," the verb matches the subject closer to it: "Neither the coach nor the players were ready."

Sentence boundaries: fragments, run-ons, and comma splices

Recognizing a complete sentence, and fixing the four ways two sentences get joined incorrectly.

Learn more: the four fixes for joining two complete sentences

A comma splice (two complete sentences joined by just a comma) is one of the most frequently tested errors. "I studied hard, I passed the test" is wrong.
Four correct ways to join two complete sentences: a period, a semicolon, a comma plus a coordinating conjunction (and, but, so, or, yet, for, nor), or making one half dependent with a word like "because" or "although."
A fragment is missing a subject, a verb, or a complete thought. "Running through the park every morning before school." looks like a sentence but has no main verb doing the action, it needs a subject and verb attached.
Test each answer choice by reading it as its own complete thought. If either side of the punctuation can't stand alone, that tells you what kind of fix the sentence needs.

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Gotcha

Here's the classic trap, almost word for word how it shows up: a sentence like "The recipe, which my grandmother wrote by hand, was hard to read." With one comma removed, it becomes "The recipe which my grandmother wrote by hand was hard to read," and that single-comma version is a common wrong answer choice. The rule is pairs: if the "which" clause is nonessential (it is here, the sentence works without it), it needs commas on both sides, not one, not zero. Answer choices that add or remove exactly one comma from a pair are testing whether you know this rule or just liked the shorter option.

A quick sanity check before you lock in an answer

Read the full sentence with your chosen answer plugged in, out loud in your head, not just the underlined portion in isolation. Most wrong answers sound fine on their own and only reveal themselves as wrong once you hear the whole sentence.

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Quick tip

If you genuinely can't tell whether a comma belongs, try reading the sentence without it and without the phrase it surrounds. If the sentence still makes complete sense, the phrase is nonessential and needs commas on both sides.

Reading about the rules is step one.

Ember has original Conventions of Standard English questions, each with the reasoning explained the same way, including exactly which rule it's testing.

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