ABSTRACT
By far, the comma is the most difficult form of punctuation to master because it serves several purposes; the rules governing its use can be difficult to apply, even when you know the rules; and some sentences require an added comma to avoid confusion, despite there being no formal rule for its addition.
The comma plays a key role in aiding readability and minimizing confusion by separating independent clauses, items in a series, dependent clauses, adjectival clauses, appositives, transitional words and phrases, introductory adverbs, adverbial phrases, participial phrases, participial and adverbial phrases in a compound sentence, absolute phrases, coordinate adjectives, parenthetical material, contrasting material, direct questions, tag questions, indirect quotations, elements in a date, elements in an address, and numbers.
No form of punctuation inspires more debate—and variation in usage—than the comma. That said, comma placement is by no means primarily subjective; in most instances, the correctness of using, or not using, a comma is generally agreed upon. Still, the uniqueness of a sentence may invite adding a comma to enhance readability even though no rule calls for it. At other times, adding an unrequired comma enriches the sentence’s meaning. Although writers will sometimes omit a normally required comma whose absence, they believe, improves readability.
