opening interjections: comma after yes, no, oh, and well

Place a comma after an interjection that opens a sentence: Yes, the shipment arrived this morning. The interjection stands outside the grammar of the clause that follows, and the comma marks that boundary. The comma signals structure, not a pause, so it is required even where a speaker would not pause. The same rule applies to the interjections okay, ah, and hey, and to why when it expresses surprise: Okay, the meeting starts at noon.

The comma after an opening no can determine the meaning of a sentence. No, parking is allowed on this street answers a question and permits parking. No parking is allowed on this street forbids parking, because without the comma, no functions as an adjective modifying parking.

Yes, no, well, and why take no comma when they function as ordinary parts of the sentence rather than as interjections. Well is an interjection in Well, the crew finished before noon but an adverb modifying before noon in Well before noon, the crew finished. Why is an interjection in Why, that is my old bicycle! but an interrogative adverb in Why is my old bicycle in the garage? When yes or no serves as the object of a verb, it belongs to the clause and takes no comma: Marcus said yes to the offer.

A fixed two-word interjection such as oh well or oh no takes a single comma after the complete expression: Oh well, the next train leaves in ten minutes. A name that follows an opening interjection is a direct address, so a second comma follows the name: Yes, Linda, the report is finished. An interjection that expresses strong feeling may stand as its own sentence with an exclamation point: Ouch! The handle is hot. An interjection in the middle of a sentence is enclosed in a pair of commas: The repair will cost, oh, about two hundred dollars.

See also comma; comma with introductory elements; direct address: commas around a name or title; exclamation point.