Master these 19 essential grammar rules to ace the ACT English section.
Subject-verb agreement means the subject of the sentence and the verb must match in number (singular or plural). The ACT will often insert distracting words or phrases between the subject and verb, or use subjects that sound plural but are singular (or vice versa), to test whether you can identify the true subject and use the correct verb form. Always locate the actual subject of the sentence (ignore any intervening descriptive phrases or clauses) and make sure the verb agrees with that subject. Watch out for indefinite pronouns like each, everyone, none, neither – these are singular and take singular verbs, even if followed by a phrase with plural nouns.
Example: The coat with the blue stripes are in the closet.
Explanation: The subject of the sentence is "coat," which is singular. The phrase "with the blue stripes" is extra information and doesn't change the subject's number. The verb should be singular "is", not plural "are." The correct sentence is: "The coat with the blue stripes is in the closet." In ACT questions, a plural verb with a singular subject (or vice versa) will be underlined as an error. The correct answer will match the verb to the subject in number.
The ACT English section tests your ability to use proper verb tense and keep tenses consistent within a sentence or passage. You must choose the verb form that logically fits the time frame of the context and remain consistent unless there's a clear reason to shift tense (such as a flashback or a change from past to present events). Common scenarios include mixing up past and present, or using the wrong tense for a sequence of events. Also, look for had (past perfect) when describing an action that was completed before another past action.
Example: She runs five miles yesterday to train for the marathon.
Explanation: This sentence describes an action (running five miles) that happened "yesterday," so it should be in the past tense. The verb "runs" (present tense) is incorrect. The correct verb is past tense "ran." The sentence should read: "She ran five miles yesterday to train for the marathon." On the ACT, verb tense questions often include answer choices with different verb forms. Check the surrounding sentences for time clues (e.g. dates, time indicators like yesterday, last year, or currently) to determine the proper tense, and ensure all verbs are consistent in context.
Pronoun questions are very common on the ACT. A pronoun must agree with its antecedent (the noun it replaces) in number (singular vs. plural) and person (first, second, third). Additionally, the meaning should be clear – it must be obvious what noun the pronoun is referring to. The ACT will test errors like using a plural pronoun for a singular noun, or using a pronoun with an ambiguous reference. To avoid ambiguity, if a sentence has two possible antecedents, the pronoun usage is likely incorrect and needs to be clarified.
Example: Each of the players must bring their own equipment to the game.
Explanation: The indefinite pronoun "Each" is singular, so the pronoun referring to it should also be singular. "Their" is plural and does not agree with "each." The sentence should use "his or her" (singular) or be rephrased in plural form. A correct revision could be: "Each of the players must bring his or her own equipment to the game." In an ACT question, you might see answer choices offering different pronouns. The correct answer would use a singular pronoun to match "each." Always identify the antecedent and make sure the pronoun agrees and clearly refers to that antecedent (if not, pick an answer that clarifies or changes the pronoun).
Ambiguous Pronoun Reference: The ACT may underline a pronoun that could refer to more than one noun. For instance, "When Jake visited Tom, he brought his notebook." – here "he" is ambiguous (it's unclear who he is). A correct revision might be, "When Jake visited Tom, Jake brought his notebook," or "..., Tom brought his notebook." Be prepared to eliminate ambiguous pronouns by replacing them with the intended noun.
Using the correct pronoun case is another rule tested on ACT English. Pronoun case refers to whether a pronoun is being used as a subject or an object in a sentence. Subject pronouns (I, he, she, they, who, etc.) are used when the pronoun is the one doing the action of the verb. Object pronouns (me, him, her, them, whom, etc.) are used when the pronoun is receiving the action or after a preposition. The ACT might include compound subjects or objects (e.g., "My friend and I/me went...") to see if you know to use "I" as a subject or "me" as an object. A common trap is in sentences like "The winner was her/she." The correct pronoun after a linking verb (was) is the subject case (she), because it is essentially saying "She was the winner."
Another frequently tested case is who vs. whom:
Example (Pronoun Case): The scholarship committee will interview my friend and I.
Explanation: In this sentence, "my friend and I" are the objects of the verb "interview" (the committee is interviewing us). Since the pronoun is an object here, we should use "me" (object case) instead of "I." The correct version is: "The scholarship committee will interview my friend and me." On the ACT, if you see a pronoun underlined in a compound structure ("and I" or "and me"), check whether that phrase is the subject or object. Remove the other noun to test it: "The committee will interview I" is clearly wrong – it should be "interview me."
Example (Who vs. Whom): Who did the teacher praise for their project?
Explanation: To decide between who and whom, turn the question into a statement: "The teacher did praise who/whom for their project." Replace who/whom with a placeholder pronoun: "The teacher did praise him for his project." Since we would use "him" (an object pronoun) in the sentence, the correct choice is "whom." The sentence should read: "Whom did the teacher praise for their project?" The ACT often provides "who" vs "whom" answer choices. Use the he/him (or she/her) test: if "he" fits, go with who; if "him" fits (remember "him" ends in m, as does whom), go with whom.
Relative pronouns (like that, which, who, whom, where) introduce clauses that describe a noun. The ACT commonly tests whether you know the difference between essential (restrictive) and non-essential (non-restrictive) relative clauses, and how to punctuate them.
Also, use the appropriate relative pronoun for the context:
Example: The car which I bought last year is already needing repairs.
Explanation: The clause "which I bought last year" is intended to specify which car, meaning it's essential information. In an essential clause about a thing, the correct relative pronoun is "that" (not "which"), and no comma is needed. The corrected sentence is: "The car that I bought last year is already needing repairs." Alternatively, if the clause were just additional info (nonessential), it would be: "The car, which I bought last year, is already needing repairs." On the ACT, an underlined "which" without a comma or a misused "that" with a comma is a sign that the relative pronoun or punctuation is incorrect. Choose the answer that uses the proper pronoun and comma usage for the clause's importance.
Adjectives and adverbs are both description words, but they are used differently. Adjectives describe nouns or pronouns, while adverbs modify verbs, adjectives, or other adverbs. Many adverbs end in -ly (quickly, effectively), but not all (e.g., well as an adverb of good). The ACT will test if you know which form to use in context. A common situation is when a linking verb (such as feel, sound, taste, look, appear) is used – these verbs should be followed by an adjective, not an adverb, because the adjective describes the subject. In contrast, action verbs should be modified by adverbs.
Example: The roses smell sweetly in the garden.
Explanation: The verb "smell" in this context is linking the roses to a description of them. We want to describe the roses (the subject), so we need an adjective, not an adverb. The correct sentence is: "The roses smell sweet in the garden." Here sweet (adjective) describes the roses. Using sweetly (adverb) would imply the roses are performing the act of smelling in a sweet manner, which doesn't make sense. On the ACT, you might see a pair like "sweet/sweetly" or "slow/slowly" underlined. Check what is being described: is it a noun (use adjective) or a verb (use adverb)? Another example: "He is a good singer" (correct, adjective describing "he") versus "He sings well" (correct, adverb describing how he sings). If a choice between good and well is offered, remember "good" is an adjective and "well" is usually an adverb (except when talking about health, e.g., "I feel well" can be correct to mean "I am healthy," but ACT usually tests the straightforward usage).
Comparative and superlative forms of adjectives and adverbs are frequently tested. Comparatives (usually ending in -er or using more) are used to compare two things. Superlatives (ending in -est or using most) are used for three or more things. The ACT may create errors by using the wrong form or by mixing up the word choices that accompany comparisons.
Key rules to remember:
Example: Between the two finalists, Aaron is the fastest sprinter.
Explanation: "Between the two finalists" indicates a comparison of two people. We should use the comparative form "faster" instead of the superlative "fastest." The correct sentence is: "Between the two finalists, Aaron is the faster sprinter." An ACT question might have an underlined word like "fastest" with answer choices including "faster." Always identify how many things are being compared. If it's two, pick the comparative (-er or more); if it's more than two, pick the superlative (-est or most).
The ACT can also test other comparison issues. One common one is incomplete comparisons: for example, a sentence like "Our car is faster." (Faster than what?) In context, the comparison should be completed (e.g., "faster than our previous car"). Additionally, watch for comparisons that must be logical – you should compare similar categories (people to people, things to things). For instance, "Her test scores were higher than any student in the class" is flawed because technically she shouldn't be compared to herself as part of "any student." It should say "higher than those of any other student in the class." These nuances are less common but can appear for top scorers.
Parallel structure means that items in a list or pairs of ideas in a sentence are presented in the same grammatical form. ACT English frequently tests parallelism in lists and in correlative conjunctions (pairs like either/or, neither/nor, not only/but also). If a sentence contains a series of actions or descriptions, each part of the series should be structured similarly. Parallel structure errors occur when one element breaks the pattern.
How it's tested: You might see a sentence where two items are in one form and the third is in a different form, making the list not parallel. Or a sentence with a comparison or a pair that isn't balanced. The answer choices will offer a way to make them consistent.
Example: She enjoys hiking, swimming, and to ride her bike.
Explanation: In this list of activities, "hiking" and "swimming" are gerunds (the -ing form), but "to ride" is an infinitive, which breaks the parallel structure. All three activities should have the same form. The correct version would be: "She enjoys hiking, swimming, and riding her bike." Now all items are gerunds, making the structure parallel.
Another example of parallelism with paired conjunctions: "He is not only a great student but also plays sports." This is not parallel because after "not only" we have a noun phrase ("a great student") but after "but also" we have a verb phrase ("plays sports"). To fix it, both parts should match. We could say, "He is not only a great student but also a talented athlete," or "He not only excels in academics but also plays sports." The ACT may underline the portion of the sentence around these conjunctions, and the correct choice will ensure the pieces after not only and but also are in the same form.
Always check elements in a list or paired ideas: they should sound balanced and have matching forms (noun with noun, verb phrase with verb phrase, adjective with adjective, etc.).
A modifier is a word or phrase that describes something. Misplaced or dangling modifiers are a favorite on ACT English because they can make a sentence confusing or unintentionally funny. The rule is that a modifying phrase should be next to the noun it's meant to describe. If it's not, the sentence may imply something illogical.
Example (Misplaced Modifier): The waiter served a dessert to the guest that was covered in chocolate.
Explanation: As written, it sounds like the guest was covered in chocolate! The modifier "that was covered in chocolate" is misplaced. It should be next to "dessert" (the thing that was actually covered in chocolate). A corrected version: "The waiter served a dessert covered in chocolate to the guest." Now the modifying phrase is immediately next to "dessert," clearly describing the dessert.
Example (Dangling Modifier): After finishing the assignment, the TV was turned on.
Explanation: The introductory phrase "After finishing the assignment" is supposed to describe who finished the assignment. However, the subject that follows is "the TV," which obviously didn't finish any assignment. This is a dangling modifier. To fix it, we must introduce the proper subject right after the comma: "After finishing the assignment, I turned on the TV." Now the modifier "after finishing the assignment" correctly describes "I" (the person who did the assignment).
On the ACT, a modifier error might be signaled by an underlined introductory phrase or a sentence that just sounds unintentionally wrong. The answer will either reposition the modifier or reword the sentence so that the modifier is next to the thing it modifies. Always check: What is this descriptive phrase referring to? Make sure that noun is present and immediately adjacent to the phrase.
A sentence fragment is a group of words that is not a complete sentence but is punctuated as one. Every complete sentence needs at minimum an independent clause, meaning it has a subject and a verb and expresses a complete thought. The ACT will test your ability to spot and fix fragments by either connecting them to a nearby sentence or adding the missing components.
Common causes of fragments on the ACT:
Example: Because she was late to the meeting.
Explanation: This is a fragment – it starts with "Because" which makes it a dependent clause expecting a result, but we never get a complete thought. To fix a fragment like this, you can attach it to a neighboring sentence or complete the thought. For example: "We had to begin without her because she was late to the meeting." Now the clause "because she was late to the meeting" is attached to an independent clause ("We had to begin without her"), forming a complete sentence.
In an ACT question, a fragment may be presented as a standalone sentence, and the answer choices might offer ways to connect it to the previous sentence or change a word like "Because" to make it a complete sentence. Another type: "For example, the many ways cultures celebrate the new year." This is a fragment (it looks like an example needs to be part of a larger statement). A fix could be: "There are many ways cultures celebrate the new year. For example, some celebrate by ..." or by merging it with the sentence before. The correct answer will ensure each sentence is grammatically complete.
A run-on sentence occurs when two or more independent clauses (complete thoughts) are joined incorrectly. A comma splice is one common type of run-on, where two independent clauses are joined with just a comma (which isn't strong enough by itself). The ACT expects you to fix run-ons by separating the clauses correctly — either with a period, a semicolon, or a comma plus a coordinating conjunction (for, and, nor, but, or, yet, so).
Signs of run-ons on the ACT: If you see a long sentence with an underlined comma, or just a long underlined portion that could be two sentences, it might be a run-on. The answer choices might include a period, semicolon, or adding a conjunction.
Example (Comma Splice Run-on): I love to write, I could do it all day.
Explanation: Here we have two independent clauses: "I love to write" and "I could do it all day," incorrectly joined by only a comma. To correct this, we have a few options:
On the ACT, the correct answer might be the one that adds "and" after the comma or changes the comma to a semicolon. Be careful: just adding a conjunction without the comma ( "I love to write and I could do it all day" ) would actually be acceptable as well, but the most straightforward fixes are as above.
Another run-on example is two sentences run together with no punctuation: "She was hungry she made a sandwich." In the answer choices, look for a period or semicolon: "She was hungry, so she made a sandwich." would also fix it. The key is that every independent clause needs a proper break. If you find two subjects and verbs that could stand alone, check that they are joined correctly. A semicolon on the ACT works just like a period (it must separate two complete thoughts), so it's often the correct fix for run-ons if offered.
Commas are the most frequently tested punctuation on ACT English. While there are many rules governing comma usage, the ACT tends to focus on a few key ones and common pitfalls. Here are the core comma rules you should know:
Example: The dancers, and the singer performed on stage.
Explanation: Here the comma is separating the compound subject "the dancers and the singer." This is an unnecessary comma that disrupts the flow of the sentence. There should be no comma between "dancers" and "and" because "the dancers and the singer" together form the full subject of the sentence. The correct sentence is: "The dancers and the singer performed on stage." An ACT English question might have a comma like this underlined to test if you can identify it as extraneous. The correct answer would be to remove the comma.
Example (Comma for nonessential clause): My friend who lives in Texas, is coming to visit.
Explanation: Whether this comma is needed depends on the context:
When tackling comma questions on the ACT, read the sentence without the commas to see if it still makes sense and check if any crucial meaning would be lost by removing the clause. If not, it's likely nonessential and needs commas (or if a comma is already there, maybe another is missing). If removing the clause would ruin the meaning, it's essential and commas should be omitted.
The semicolon is tested as a tool to connect closely related sentences. The rule is straightforward: a semicolon (;) links two independent clauses without a conjunction. In other words, what comes before a semicolon must be a complete sentence, and what comes after must also be a complete sentence. Semicolons on the ACT often appear in questions where the difference between choices is how sentences are separated.
When to use a semicolon:
Example: The experiment failed, the results were inconclusive.
Explanation: This is a comma splice (two independent clauses joined by a comma). One correct fix is to use a semicolon: "The experiment failed; the results were inconclusive." Now each side of the semicolon is a complete sentence, and the semicolon properly joins them. On the ACT, if you see a semicolon in one of the answer choices, check that the phrases on both sides are independent clauses. If one side isn't a full sentence, a semicolon would be wrong. Conversely, if you have a run-on situation, the answer with a semicolon might be the correct solution.
Remember: A semicolon should be able to be replaced by a period without breaking grammar. You should not use a semicolon before a coordinating conjunction (FANBOYS) – that's what commas are for. And you shouldn't use a semicolon to connect an independent clause to a fragment (that's what colons or commas might do in certain cases).
Colons are used to introduce or emphasize information, but they have a strict rule: what comes before a colon must be an independent clause (a complete sentence). What comes after a colon can be almost anything – a single word, a phrase, a list, or another clause – as long as it elaborates on or explains the first part. The ACT usually tests colons by seeing if students know when a colon is appropriate versus when it's not.
Common uses of colons:
The ACT might give an option with a colon or have a colon in the sentence and ask if it's used properly. Often, a common mistake is using a colon after a phrase like "such as" or "including," which already signals a list, or placing a colon when the lead-in is not a full sentence.
Example: She was excited about her new job, including: a higher salary, better benefits, and a shorter commute.
Explanation: The phrase before the colon, "She was excited about her new job, including," is not an independent clause (it's actually incomplete because of "including"). Therefore, the colon is incorrectly used here. One way to fix it is to remove the colon: "She was excited about her new job, including a higher salary, better benefits, and a shorter commute." However, that sentence is a bit awkward with "including." A better revision might be: "She was excited about her new job for many reasons: a higher salary, better benefits, and a shorter commute." Now "She was excited about her new job for many reasons" is a complete thought, and the colon appropriately introduces the list of reasons.
On ACT English, correct answers with colons will ensure the clause before the colon is complete. If you see something like "such as:" or an incomplete lead-in before a colon, that's likely wrong. Check answer choices for either removing the colon or restructuring the sentence to use the colon correctly.
Dashes (specifically the em-dash — in writing, though on the test it might just appear as a standard dash) are less frequent but still tested. Dashes can be a bit more stylistic, but there are two main ways they are used on the ACT:
Example: My sister — who just graduated college — is moving to Canada.
Explanation: In this sentence, the dashes are used as a pair to set off the clause "who just graduated college," which is extra information about "my sister." This is a correct use of dashes for a nonessential clause. An ACT question might present this sentence with one dash and one comma, or two commas, etc., to test consistency and correctness. The correct answer would use either two commas or two dashes to enclose the clause, but not mix them. Using dashes adds emphasis, whereas commas would be a more neutral tone – grammatically both could be correct if offered, but the ACT usually only offers one consistent punctuation choice as correct.
Another example: He finally faced his biggest fear — heights. This single dash is used like a colon to introduce what his fear actually was. The clause before the dash "He finally faced his biggest fear" is independent, so the dash is appropriately used to introduce the explanation "heights." If this were an ACT item, a wrong answer might use a comma instead ("fear, heights" – incorrect) or no punctuation ("fear heights" – not clear). The dash (or a colon) would be the correct choice.
In summary, remember that dashes can replace commas or colons in certain situations:
Apostrophe questions are common and usually straightforward if you know the rules. Apostrophes are used in two main ways on the ACT:
Forming Possessives:
Contractions: An apostrophe can take the place of missing letters:
The ACT often tests commonly confused possessive vs contraction pairs:
Example: The puppy chased it's tail around the yard.
Explanation: "it's" with an apostrophe means "it is," but in this sentence we want the possessive form to talk about the puppy's tail. The correct word is "its" without an apostrophe. The corrected sentence: "The puppy chased its tail around the yard." On the ACT, you might see an underlined "its" or "it's" and the answer choices will swap them or offer "his"/"her." Remember that its (no apostrophe) is possessive. A quick check: try reading "it's" as "it is" – if it doesn't fit, you need "its."
Example 2: All of the students papers were graded.
Explanation: As written, "students papers" is plural "students" with no apostrophe, which is incorrect for showing possession. If all the papers belonging to the students were graded, we need a plural possessive: "students' papers." The apostrophe after students indicates the papers of the students. If it were one student's papers, it would be "student's papers." The ACT might underline a phrase like "students papers" to test if you know to add an apostrophe. The correct answer would likely insert an apostrophe in the right place. Always ask: is the noun supposed to own something? If yes, add an apostrophe appropriately. If the noun is just plural with no possession, no apostrophe is needed (e.g., "many students attend the lecture" – just a plural, no ownership).
The ACT will sometimes test vocabulary-in-context or commonly confused words that aren't strictly grammar rules but are part of standard English usage. These usually appear as questions where all the answer choices are different words that sound similar or have related meanings. To ace these, you should know the differences between these commonly confused terms. We've already covered some in the Apostrophes section (its/it's, their/they're/there, etc.), but here are more pairs and groups to watch for:
Example: She is more interested in biology then in chemistry.
Explanation: This sentence should be making a comparison, which calls for "than," not "then." Then refers to time/order, whereas than is the comparative word. The corrected sentence: "She is more interested in biology than in chemistry." On the ACT, an answer choice swap between than and then is a red flag to check the context. In a comparison, than is correct.
Another Example: I could of finished the project earlier if I hadn't procrastinated.
Explanation: This tests an idiomatic misuse. "Could of" is a mishearing of "could've" (which is "could have"). The correct phrase is "could have finished." The ACT might include "of" vs "have" in the choices for sentences like this. Always remember that after modal verbs like could, should, would, the correct word is "have" (or the contraction 've), not the preposition "of."
When you encounter a question where all the options are different words, read the sentence carefully and think about the meanings. Replace the underlined word with what you believe logically fits (even in your own words) and then pick the choice that matches that meaning.
Idioms are phrases or expressions that are accepted as correct in standard English usage, often with specific prepositions or word pairings. These do not always follow a clear rule – they are based on conventional usage. The ACT sometimes tests idiomatic usage, especially with prepositions after certain verbs/adjectives or with pairs of words that go together. Essentially, you have to know or "feel" what sounds correct to a fluent speaker.
Common idiomatic usage points:
Because idioms are numerous, the ACT tends to focus on the most common ones. If you're a native speaker or very fluent, trust your ear sparingly – make sure to double-check that the phrase is actually the standard usage and not a common error. When in doubt, read the whole sentence with each preposition or wording from the answer choices and see which one makes a logical, idiomatic phrase.
Example: The treasure was divided between the three explorers.
Explanation: The word "between" is typically used only with two parties. For three or more, the idiomatically correct word is "among." So the sentence should read: "The treasure was divided among the three explorers." On the ACT, you might see a preposition underlined and alternatives given (between/among, to/with, etc.). Knowing that "between A and B" (two things) vs "among several" is the rule helps you choose "among" in this case.
Example 2: She insisted for getting a refund after the show was canceled.
Explanation: The verb "insist" idiomatically pairs with "on" (or "insist that…" in a clause). The correct phrasing is "insisted on getting a refund." The ACT could test this by underlining "insisted for" and offering "insisted on" as an option. Other similar examples: "concerned about [something]" (not concerned for in that context), "in accordance with," "prior to," etc.
Strategy: There isn't a universal rule for every idiom – it's about what sounds correct in established usage. If you're unsure, eliminate choices that you know are grammatically wrong first. Often the idiom questions have one option that just "sounds right" to a well-trained ear. Studying a list of common ACT idioms (like those involving preposition use) can be very helpful for non-native speakers or anyone who wants extra confidence.
Beyond pure grammar, the ACT English section highly values conciseness and clarity. Often, the best answer is the shortest one that still preserves the meaning of the sentence. Redundancy means using more words than necessary or repeating information that's already clear from context. The ACT will include answer choices that cut out fluff or combine sentences efficiently. High-scoring students know that if an underlined portion sounds wordy or repetitive, a more concise alternative is likely correct – as long as it doesn't omit any crucial detail or change the meaning.
Things to watch for:
When a sentence or phrase is underlined and one answer choice is "DELETE" or "OMIT," strongly consider it – often the test is whether you recognize that the underlined portion isn't needed at all. The "OMIT/Delete" option is frequently correct when the original text is redundant or wordy.
Example: In order to be able to succeed, you must study hard.
Explanation: The phrase "In order to be able to" is verbose. This can be distilled without losing meaning. Simply saying "To succeed, you must study hard." is clearer and more concise. The meaning ("you must study hard if you want to succeed") stays the same. An ACT question might underline "In order to be able to" and the shortest answer choice would be "To." That would be the best choice because it eliminates unnecessary words.
Another Example: The reason why she left is because she was exhausted.
Explanation: "The reason why ... is because" is a common redundancy. "Because" already conveys the reason, so saying "the reason is because" is repetitive. A concise fix is: "She left because she was exhausted." or "The reason she left is that she was exhausted." On the ACT, an answer might remove "The reason why ... is because" structure entirely for a more direct phrasing. The correct answer removes duplication of meaning.
In summary, for conciseness:
Mastering the rules is half the battle – applying them under ACT conditions is the other half. Here are some targeted study and test-taking tips for grammar questions on the ACT English section:
By thoroughly learning these grammar rules and applying these strategies, you'll be well-equipped to tackle the ACT English section with confidence. Remember that the test repeats these grammar principles over and over, so the effort you put into mastering them will pay off on test day. Good luck, and happy studying!