ACT key terms

The rule that a verb must match its subject in number and person, so a singular subject takes a singular verb and a plural subject takes a plural verb, even when words separate them.

A group of words placed between a subject and its verb, often a prepositional phrase, that does not change the subject's number and should be mentally set aside when checking agreement.

A singular word naming a group of people or things, such as team or committee. In American usage it usually takes a singular verb unless members are acting individually.

A pronoun that does not point to a specific person or thing, such as everyone, each, none, or several. Many are singular and take singular verbs, while others are plural.

The requirement that a pronoun match its antecedent in number and gender, so a plural noun takes they and a singular noun takes he, she, or it.

The noun or noun phrase that a pronoun refers back to. Clear writing keeps the antecedent obvious so readers know exactly whom or what the pronoun means.

A pronoun whose antecedent is unclear because two or more nouns could reasonably be the one it refers to, forcing the reader to guess the intended meaning.

An error made by joining two complete sentences with only a comma. It can be fixed with a period, a semicolon, or a conjunction after the comma.

Two or more independent clauses fused together with no punctuation or with insufficient punctuation between them, so the boundary between complete thoughts is lost.

A group of words containing a subject and a verb that expresses a complete thought and can stand alone as a sentence.

A group of words with a subject and verb that cannot stand alone as a sentence because it begins with a subordinating word or functions as a noun, adjective, or adverb.

One of the seven connecting words for, and, nor, but, or, yet, so, used to link words or clauses of equal grammatical rank, often preceded by a comma when joining independent clauses.

A word such as because, although, or when that introduces a dependent clause and signals how it relates to the main clause.

A clause that adds extra information but is not needed to identify the noun it describes, so it is set off by commas; an essential clause takes no commas.

A word, phrase, or clause that is necessary to identify which person or thing is meant and therefore is not set off by commas.

A descriptive phrase that seems to modify the wrong word, usually because the noun it was meant to describe is missing from the sentence.

A descriptive word or phrase placed too far from the word it describes, so the sentence suggests an unintended or confusing meaning.

The practice of expressing items in a list or comparison in the same grammatical form, such as all nouns or all verbs ending in -ing, for balance and clarity.

The quality of expressing an idea in the fewest words needed without losing meaning, avoiding redundancy such as repeating an idea twice in different words.

Unnecessary repetition of meaning, as when a phrase says the same thing twice, which weakens writing and is a common target of revision questions.

A word or phrase such as however, therefore, or in addition that shows the logical relationship between sentences or ideas and guides the reader.

An adverb like however, moreover, or consequently that links ideas across clauses; when joining two independent clauses it needs a semicolon before and a comma after.

The punctuation mark used to show possession or to mark omitted letters in contractions; it never forms a simple plural, a frequent trap in usage questions.

The grammatical form showing ownership, usually made with an apostrophe and s for singular nouns and an apostrophe after the s for plural nouns.

A shortened form in which an apostrophe replaces omitted letters, such as it's for it is or they're for they are, distinct from possessive forms.

A punctuation mark introducing a list, explanation, or quotation after a complete sentence; what follows should relate directly to the clause before it.

A punctuation mark used between two closely related independent clauses without a conjunction, or between items in a list that already contain commas.

A comparison of two quantities by division, often written as a fraction or with a colon, showing how many times one value contains another.

An equation stating that two ratios are equal, used to solve for an unknown value when quantities scale at the same rate.

A rate expressed per one unit of a given quantity, found by dividing one quantity by the other, such as miles per hour or cost per item.

An equation whose graph is a straight line, typically written y = mx + b, where m is the slope and b is the y-intercept.

A measure of a line's steepness, calculated as the change in y divided by the change in x between two points on the line.

The point where a graph crosses the vertical axis, occurring where x equals zero; in y = mx + b it is the value b.

An equation of degree two, usually written ax squared plus bx plus c equals zero, whose solutions can be found by factoring, completing the square, or the quadratic formula.

A relationship in which each input value is paired with exactly one output value, often tested by checking whether a graph passes the vertical line test.

The set of all allowable input values for a function, sometimes limited by context or by values that would make a denominator zero.

The set of all output values a function can produce, found by applying the rule to every value in the domain.

The arithmetic average of a data set, found by adding all values and dividing by the number of values.

The middle value of a data set arranged in order, or the average of the two middle values when the number of values is even.

A number between zero and one expressing how likely an event is, computed as the number of favorable outcomes divided by the total number of equally likely outcomes.

The central point a passage communicates about its topic, broad enough to cover the whole text but specific enough to exclude details.

A specific fact, example, or reason in a passage that explains, illustrates, or proves the main idea.

A conclusion a reader draws by combining stated information with reasonable logic, going slightly beyond what the text says explicitly.

The attitude a writer conveys toward the subject or audience, revealed through word choice and details rather than stated directly.

The perspective from which a text is told, such as first person, third-person limited, or third-person omniscient, affecting what information the reader receives.

The reason a writer creates a text, commonly to inform, persuade, entertain, or explain, which shapes the content and style of the passage.

Determining the meaning of a word from how it is used in a specific sentence, since many words carry several possible meanings.

A testable prediction about the outcome of an experiment, often stated as an if-then relationship between variables.

The factor a researcher deliberately changes or manipulates in an experiment to observe its effect on another factor.

The factor that is measured or observed in an experiment and that responds to changes in the independent variable.

A factor held constant across all trials of an experiment so that it cannot influence the outcome and confound the results.

The comparison group in an experiment that does not receive the treatment, providing a baseline against which the experimental group's results are judged.

An organized grid of rows and columns presenting measurements or observations, often the source for spotting trends or calculating averages in a study.

A general direction in which data move, such as increasing, decreasing, or leveling off, which a reader identifies by comparing values across a table or graph.

A single sentence that states the main claim of an essay and previews the reasoning that will support it, usually placed at the end of the introduction.

The sentence, often first in a paragraph, that announces the paragraph's central point and ties it to the essay's larger argument.

A point of view opposing the writer's claim that the writer acknowledges and then answers, strengthening the essay by showing the issue has been considered fairly.

Specific facts, examples, statistics, or quotations used to support a claim and persuade readers that the argument is credible.