Commas

Punctuation might seem like a minor detail, but its history reveals just how essential it is to clear communication. Before standardized punctuation existed, written text was one long, unbroken stream of words. Readers had to guess where one idea ended and the next began. The comma evolved over centuries specifically to solve this problem—it acts as a brief pause signal, telling readers how to group words and separate ideas within a sentence.

Today, comma questions are among the most frequently tested items on the ACT English section. Knowing when to insert a comma—and just as importantly, when not to—can mean the difference between a correct and incorrect answer. The central question is straightforward: what are the specific, rule-based situations that require a comma?

On the ACT, comma usage is not about feeling or intuition—it follows specific grammatical rules. If you cannot name a rule that justifies a comma, then the comma should not be there. The ACT tests roughly five major comma principles, and understanding each one gives you a reliable framework for every comma question you encounter.

The flowchart above is your primary strategy tool. When you face a comma question on the ACT, mentally run through these four checks. The ACT deliberately designs wrong answers that "sound right" when you read a sentence aloud, so relying on your ear alone will lead to mistakes. Instead, anchor your decision in the specific rule. Notice that the final box—"Do NOT add a comma"—is critical. On the ACT, removing an unnecessary comma is just as common a correct answer as adding one.

Rule 1: Introductory Elements

An introductory element is any word, phrase, or dependent clause that appears before the main subject and verb of a sentence. It provides context—when, where, why, or how—before the core action begins. A comma separates this opening material from the independent clause that follows. For example: Running late for class, Maria grabbed her backpack and sprinted down the hall. The participial phrase "Running late for class" modifies Maria, and the comma tells the reader where the introduction ends and the main clause begins.

Rule 2: FANBOYS Between Independent Clauses

When two independent clauses (each with its own subject and verb, capable of standing alone) are joined by a coordinating conjunction—for, and, nor, but, or, yet, so (FANBOYS)—a comma must appear before the conjunction. Compare: Jake studied all night, but he still felt unprepared. Both "Jake studied all night" and "he still felt unprepared" are complete sentences, so the comma is required. However, in Jake studied all night but still felt unprepared, the second part lacks its own subject, making it a compound predicate—no comma needed.

Rule 3: Items in a Series

When a sentence lists three or more parallel items—words, phrases, or clauses—commas separate them. Example: The recipe calls for flour, sugar, eggs, and butter. The ACT accepts both the Oxford comma (comma before "and") and the non-Oxford style, but wrong answers often omit commas between items entirely or add commas where only two items exist. Remember: two items joined by "and" do not need a comma.

Rule 4: Nonessential (Nonrestrictive) Elements

A nonessential element provides extra information that can be removed without changing the core meaning of the sentence. These elements must be set off by commas on both sides (or one side if the element starts or ends the sentence). Consider: My brother, who lives in Austin, is visiting next week. If you have only one brother, the clause "who lives in Austin" is extra detail—nonessential. But in The student who submitted the essay early received bonus points, the clause identifies which student—it's essential, so no commas.

Rule 5: No Unnecessary Commas

This is arguably the most important ACT comma rule. Never place a comma between a subject and its verb, between a verb and its direct object, or between two items in a compound structure joined by a single conjunction. For instance, The mayor of the city, announced new policies is incorrect because the comma splits the subject ("The mayor of the city") from its verb ("announced"). On the ACT, if you see a comma that doesn't match any rule, choose the answer that removes it.

Understanding the rules is one thing; recognizing how the ACT frames those rules in actual questions is another. The test writers have favorite patterns they use repeatedly. Below is a visual guide to the most common sentence structures you'll encounter, showing exactly where commas belong and where they don't.

Let's walk through an ACT-style question step by step. The passage reads:

The question asks: Which is the best punctuation for the underlined portion "researchers, decided to adjust the temperature, and humidity"?

ACT test writers are skilled at creating answer choices that "sound" correct when read aloud but violate comma rules. Here are the most common traps alongside the strategies you can use to avoid them.

Comma questions on the ACT don't exist in isolation—they often appear alongside answer choices that use semicolons, colons, dashes, or periods. Understanding how commas relate to these other marks helps you eliminate wrong answers more efficiently. The table below shows when each punctuation mark is the better choice.