Punctuation

Commas with items in a series (list)

When three or more items are presented in a series, those items should be separated from one another with commas. Items in a series may be single words, phrases, or clauses.

Example sentence with editing. Original sentence: Bubbles of air, leaves, ferns, bits of wood and insects are often found trapped in amber. Revised sentence: Bubbles of air, leaves, ferns, bits of wood, and insects are often found trapped in amber.

Example sentence with editing. Original sentence: My uncle willed me all of his property, houses and warehouses. Revised sentence: My uncle willed me all of his property, houses, and warehouses.

Did the uncle will his property and houses and warehouses — or simply his property, consisting of houses and warehouses? If the first meaning is intended, a comma is necessary to prevent ambiguity.

Example sentence with editing. Original sentence: The activities include a search for lost treasure, dubious financial dealings, much discussion of ancient heresies and midnight orgies. Revised sentence: The activities include a search for lost treasure, dubious financial dealings, much discussion of ancient heresies, and midnight orgies.

Without the comma, the people seem to be discussing orgies, not participating in them. The comma makes it clear that midnight orgies is a separate item in the series.

Although some disciplines omit the comma between the last two items, be aware that its omission can result in ambiguity or misreading. Check the style guidelines for the discipline in which you are writing.

Exercises:

Major uses of the comma 1

Major uses of the comma 2

All uses of the comma