Usage 1: Creating a list of items.
Use commas between listed items. There should be one less comma than the number of items listed.
- Example: I shower, water my plants, and journal in the morning.
Exception: If what you’re listing already has commas or punctuation marks, the listed items should be separated by semicolons instead.
- Example: Some of the books I read this summer were: Girl, Woman, Other; Kim Jiyoung, Born 1982; and Goodbye, Things: The New Japanese Minimalism.
Usage 2: Independent clauses.
Use a comma between independent clauses to combine them. Independent clauses are phrases that can stand as separate sentences if needed. Independent clauses are separated by conjunctions (FANBOYS): for, and, nor, but, or, yet, so.
- Example: It was cold outside yesterday, so I think it’ll be cold outside today.
Usage 3: Introductory phrases.
There should be a comma after an introductory phrase, which introduces the topic and often sets the scene. These phrases are dependent clauses and thus are not separated by conjunctions.
- Example: When I went to India, I realized it was hotter than I had expected.
Usage 4: Adjectives.
Use a comma to separate two or more adjectives that describe the same word.
- Example: I chose to wear a dark, thick sweater.
Exception: Some adjectives aren’t separated by commas. Replace the comma with “and”, and if the sentence still makes sense, the comma is correct.
- Example: My smart, funny elder brother picked me up from school.
Usage 5: Inessential phrases.
Phrases that provide extra, descriptive information should be separated by commas. If the phrase were taken out, the sentence should still sound correct.
- Example: My cat, whom I adopted a month ago, gets excited when people visit.