Comma Usage — SAT Reading & Writing Explained
Commas have specific, rule-based uses: they join independent clauses with a conjunction, set off introductory elements, separate items in a list, and enclose non-essential clauses. Using commas where not needed — or missing them where required — is a frequent error.
The Core Idea
A comma marks a specific grammatical structure. It is not placed wherever you pause when reading aloud. Each comma in a correct sentence can be justified by a rule.
Comma Rules
I studied hard, and I passed. [comma + FANBOYS between two independent clauses]
After the exam, I celebrated.
I bought apples, oranges, and bananas.
My sister, who lives in Boston, visited me. [clause can be removed without changing the meaning]
Thank you, Ms. Smith, for your help.
When Not To Use Commas
Between subject and verb: 'The tall professor, wrote the book.' ✗
Before a subordinating conjunction: 'I stayed home, because I was sick.' ✗ (usually)
Before a restrictive (essential) relative clause
Common Errors to Avoid
Adding a comma between subject and verb
Missing the comma after introductory elements
Incorrectly treating essential clauses as non-essential and adding commas
How This Connects to Other Topics
Related to Semicolons/Colons and Sentence Boundaries
Practice: Comma Usage
5 SAT-style questions. Select your answer and get an instant explanation.
My sister, who lives in Denver works in education.
Which revision uses commas correctly?
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