The comma serves two main purposes: First and most important, it separates elements, such as items in a series. Second, just as an apostrophe indicates missing letters, so a comma indicates a missing word or words.
The comma serves two main purposes: First and most important, it separates elements, such as items in a series.
Second, just as an apostrophe indicates missing letters, so a comma indicates a missing word or words: The bread was fresh; the salad, crisp; the terrine, divine.
Separating items in a series
“To my parents, Ayn Rand and God.”
That classic example—purportedly from a book’s actual dedication page—shows the confusion that can ensue when a comma is omitted before and. Including the comma before and (called a serial comma) clears up the ambiguity.
Follow these rules when writing a series of items: