Comma

Lists

In general, use commas to separate entries of lists of three or more items. The Oxford comma (the comma before and in such a list) is mandatory.

Examples

• Correct: We ordered sandwiches, onion rings and dip, and ice cream.

• Incorrect: We ordered sandwiches, onion rings and dip and ice cream.

Interchangeable adjectives

Use a comma to separate two interchangeable adjectives.

Examples

• He is a dedicated, trustworthy boy.

  • He is a trustworthy, dedicated boy.

Independent clauses

Use a comma at the end of the first clause in a sentence with two independent clauses joined by a coordinating conjunction (and, but, for, or, nor, so, yet).

Examples

• She played the piano, and she lost track of time.

Such commas may be omitted if both clauses are very short.

Examples

• She sings and he dances.

Parenthetical information

Parenthetical expressions (those which clarify or explain something but are not essential to the sentence) should be set off with commas. This is often relevant to names which appear after an identifier. If the identifier is enough to determine the identity of the thing being referred to, then the name is parenthetical.

Examples

• Correct: Leonardo da Vinci's masterpiece, the Mona Lisa, resides in the Louvre.

  • The renowned actor Michael Caine has starred in well over one hundred films.

• Incorrect: Leonardo da Vinci's masterpiece the Mona Lisa resides in the Louvre.

  • The renowned actor, Michael Caine, has starred in well over one hundred films.

Introductory phrases

Most introductory phrases, including dependent clauses, participial phrases, and adverbial phrases, should usually be set off with a comma. However, sentence-initial coordinating conjunctions should never be followed by a comma. The only exception is if the comma is the first of two commas which set off parenthetical information.

Examples

• Correct: Having forgotten to buy milk, John needed to go back to the store.

  • But the Senate struck down the bill.

  • So, since I read the book, I am excited for its film adaptation.

• Incorrect: Having forgotten to buy milk John needed to go back to the store.

  • But, the Senate struck down the bill.

  • So since I read the book, I am excited for its film adaptation.

Other uses

The comma is easily the most versatile punctuation mark, with far too many uses to detail here. As a general principle, you should employ the comma to enhance clarity or readability. However, remember that using too many commas may achieve the opposite effect.

See also

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