Oxford comma (serial comma)

The Oxford comma, also called the serial comma, is the comma that precedes the conjunction introducing the final item in a list: The studio supplied a guitar, a bass, and drums. The name Oxford comma, first recorded in 1978, comes from its use by Oxford University Press; the same mark is also called the Harvard comma, named for Harvard University Press. Using the Oxford comma and omitting it are equally standard: The studio supplied a guitar, a bass and drums. Only this final comma is a matter of style; the commas that separate the preceding items are required. Choose one practice and apply it to every list in the same piece of writing. A list of two items takes no comma before the conjunction: a guitar and drums.

Our usage dictionary recommends the Oxford comma, because a writer who uses it in every list never has to judge which lists need it. Writers who omit the Oxford comma must place a comma between the penultimate and final items wherever its absence would cause a misreading. Daniel thanked his parents, Ana, and Tom means that Daniel thanked his parents and also Ana and Tom. Without the Oxford comma, Daniel thanked his parents, Ana and Tom can be read to mean that Ana and Tom are his parents.

The Oxford comma can itself cause a misreading when the second item could rename the first. In Chris thanked his sister, Emily, and Sam, Emily can be read as his sister’s name. Reorder the list so that no item could rename the item preceding it: Chris thanked Sam, Emily, and his sister.

When the items in a list contain commas of their own, semicolons separate the items, and the final semicolon precedes the conjunction: The tour stopped in Austin, Texas; Reno, Nevada; and Salem, Oregon.

See also appositives: comma use; comma; commas in lists; semicolon.