Overview
Comma questions test whether students can apply the four core comma rules: use after introductory elements, use around nonrestrictive (nonessential) clauses, use in a series of three or more items, and use before a coordinating conjunction joining two independent clauses. Comma questions also test the ability to identify comma splices (two independent clauses joined by a comma alone) and unnecessary commas that disrupt sentence flow. Punctuation questions make up roughly 26% of the Standard English Conventions section. Students must determine whether a comma is required, optional, or forbidden at a given position.
Key Points
1. Commas in a Series (Lists)
Use commas to separate three or more items in a list. The SAT consistently uses the Oxford comma (also called the serial comma) — the comma before the final “and” or “or.”
Correct: “She studied biology, chemistry, and physics.” Wrong: “She studied biology, chemistry and physics.” (missing Oxford comma)
This rule also applies to a series of phrases or clauses: “He ran to the lab, collected the samples, and analyzed the data.”
2. Commas After Introductory Elements
When a sentence begins with a dependent clause, a long participial phrase, or a prepositional phrase, a comma is placed between the introductory element and the main clause.
| Introductory Type | Example |
|---|---|
| Dependent clause (subordinating conjunction) | “Although the experiment failed, the data was valuable.” |
| Participial phrase | ”Having reviewed the results, the team revised their hypothesis.” |
| Long prepositional phrase | ”In the early years of the twentieth century, scientists debated the structure of the atom.” |
| Single-word adverb | ”Nevertheless, the study continued.” |
Key rule: No comma is needed when the dependent clause follows the main clause. “The data was valuable although the experiment failed.” (no comma — dependent clause at the end)
3. Commas Around Nonrestrictive Clauses
Restrictive clauses are essential to the meaning of the sentence. They identify which specific person or thing is being discussed. Do NOT use commas.
Nonrestrictive clauses add extra, optional information. Remove them and the sentence’s core meaning does not change. USE commas (before and after).
| Type | Example | Commas? |
|---|---|---|
| Restrictive | ”The scientist who discovered penicillin was Fleming.” | No |
| Nonrestrictive | ”Fleming, who discovered penicillin, won the Nobel Prize.” | Yes |
| Restrictive | ”The report that the team submitted was rejected.” | No |
| Nonrestrictive | ”The report, which was submitted last week, was rejected.” | Yes |
Test: Remove the clause. If the sentence still clearly identifies the right noun, the clause is nonrestrictive → use commas.
4. Commas Before Coordinating Conjunctions (FANBOYS)
Use a comma before a coordinating conjunction (For, And, Nor, But, Or, Yet, So) ONLY when it joins two complete independent clauses.
Correct (two independent clauses): “She studied the material, and she passed the exam.” Wrong (one subject, two verbs): “She studied the material, and passed the exam.” (remove comma — same subject doing both)
| Correct (two clauses) | Correct (shared subject) |
|---|---|
| “He trained hard, but he did not qualify." | "He trained hard but did not qualify." |
| "She arrived early, and she helped set up." | "She arrived early and helped set up.” |
5. Comma Splices — When Commas Are Wrong
A comma splice occurs when two independent clauses are joined by only a comma (no conjunction). This is always wrong on the SAT.
Wrong: “The experiment failed, the team redesigned it.” Correct options:
- Period: “The experiment failed. The team redesigned it.”
- Semicolon: “The experiment failed; the team redesigned it.”
- Comma + conjunction: “The experiment failed, so the team redesigned it.”
- Subordinating conjunction: “Because the experiment failed, the team redesigned it.”
Comma splice with conjunctive adverbs: Words like “however,” “therefore,” “moreover,” “consequently” are NOT coordinating conjunctions. A comma before them creates a splice. Wrong: “The study was flawed, however the results were interesting.” Correct: “The study was flawed; however, the results were interesting.”
6. When NOT to Use a Comma
The SAT also tests the removal of unnecessary commas:
| Wrong placement | Rule | Corrected |
|---|---|---|
| Between subject and verb | Never separate subject from its verb | ”The scientist, discovered a cure.” → “The scientist discovered a cure.” |
| Between verb and object | Never separate verb from its direct object | ”She described, the experiment.” → “She described the experiment.” |
| Before a restrictive clause | No commas around essential clauses | ”The book, that she recommended, was sold out.” → “The book that she recommended was sold out.” |
| After a short introductory phrase | Optional / usually omitted | ”In 2024, scientists found…” is acceptable; “In 2024 scientists found…” is also correct. |
Pitfalls and Common Mistakes
Pitfall 1: Comma Splice with “However” or “Therefore”
Description: Students see a transition word like “however” or “therefore” and assume a comma before it is sufficient to join two independent clauses.
Wrong: “The data was conclusive, however the team wanted more evidence.” Correct: “The data was conclusive; however, the team wanted more evidence.” Fix: Conjunctive adverbs (however, therefore, moreover, consequently, furthermore, nevertheless) require a semicolon before them — not a comma — when placed between two independent clauses.
Pitfall 2: Comma Between Subject and Verb
Description: A long introductory phrase ends close to the subject, and students insert an extra comma between the subject and its verb.
Wrong: “The team of researchers working in three different laboratories, published the study.” Correct: “The team of researchers working in three different laboratories published the study.” Fix: Never place a single comma between a subject and its main verb, no matter how long the subject phrase is.
Pitfall 3: Restrictive vs. Nonrestrictive Confusion
Description: Students add commas around a restrictive clause (essential information) or omit commas from a nonrestrictive clause (extra information).
Wrong: “The drug, that cured the disease, was developed in 2020.” (commas around essential clause) Correct: “The drug that cured the disease was developed in 2020.” Fix: Ask: “If I remove this clause, does the sentence still clearly identify the specific noun?” If removing the clause changes the meaning, it is restrictive — no commas.
Pitfall 4: Missing Oxford Comma
Description: Students omit the comma before the final “and” in a three-item list, sometimes creating ambiguity.
Wrong: “The study examined diet, exercise and sleep.” Correct: “The study examined diet, exercise, and sleep.” Fix: Always include the Oxford comma in SAT lists. The SAT consistently tests this as the correct choice.
Pitfall 5: Adding a Comma Before a Conjunction Joining Two Verbs
Description: When “and” or “but” connects two verb phrases with the same subject (not two full independent clauses), no comma is needed. Students add one unnecessarily.
Wrong: “She collected the data, and analyzed the results.” Correct: “She collected the data and analyzed the results.” (same subject “she” — not two independent clauses) Fix: Check whether the conjunction is joining two independent clauses (each with its own subject) or just two verbs sharing the same subject. Only the former requires a comma.
Related Entries
- Sentence_Boundaries — Comma splices and the four ways to fix run-ons
- Punctuation_Semicolons_Colons_Dashes — Semicolons, colons, and dashes as alternatives to commas
- Pronoun_Antecedent_Agreement — Who/which/that in restrictive vs. nonrestrictive clauses
- Modifier_Placement — Introductory participial phrases always followed by a comma
- Parallel_Structure — Commas in parallel lists and series
Quick Reference Card
| Comma Rule | Use Comma | No Comma |
|---|---|---|
| Introductory element | After dependent clause or long phrase at start | When dependent clause follows main clause |
| Nonrestrictive clause | Around clause that can be removed | Around essential restrictive clause |
| Series/list | Between all items (Oxford comma included) | Never between only two items |
| FANBOYS conjunction | Before FANBOYS joining two full clauses | Before FANBOYS joining two verbs (one subject) |
| Comma splice | Never — use period, semicolon, or conjunction | Do not join two clauses with comma alone |
| Subject-verb | Never between subject and its verb | — |