Commas

A comma is a punctuation mark used to indicate a short pause within a sentence or to separate elements. It helps clarify meaning by signaling relationships between ideas without ending a sentence.

Common uses include listing items; separating introductory elements such as words, phrases, or dependent clauses; enclosing nonessential information; and introducing or setting off direct quotations. Commas also appear in direct address, to identify the person being spoken to.

In compound sentences, a comma typically precedes a coordinating conjunction (and, but, or, nor, for, so, yet) to link two independent clauses. American practice generally favors this; British usage has been more flexible. The serial comma before the final item in a list is optional in many guides, though some styles require it to avoid ambiguity (e.g., red, white, and blue vs. red, white and blue).

In numbers, commas separate thousands in most English texts; in some locales a period serves that role. In dates, a comma usually follows the day in "Month Day, Year" format. In addresses, a comma separates the city from the state or country.

Typography and style: use no space before a comma and one space after. Avoid comma splices by pairing independent clauses with a conjunction or by breaking into separate sentences. Misplacing a modifier or enclosing nonessential information can change meaning, so commas should clearly reflect the intended structure of a sentence.