Punctuation

Comma after introductory phrase or clause

Example sentence with editing. Original sentence: Because tuberculosis can be inactive for months or years many carriers are totally unaware that they are infected. Revised sentence: Because tuberculosis can be inactive for months or years, many carriers are totally unaware that they are infected.

Example sentence with editing. Original sentence: Fortunately new antibiotics are effective in wiping out the infection. Revised sentence: Fortunately, new antibiotics are effective in wiping out the infection.

Example sentence with editing. Original sentence: Even with the best antibiotics the treatment takes about nine months and has significant side effects. Revised sentence: Even with the best antibiotics, the treatment takes about nine months and has significant side effects.

The comma tells readers that the introductory element has come to a close and that the main part of the sentence is about to begin.

The most common introductory word groups are phrases and clauses functioning as adverbs and phrases functioning as adjectives.

Comma with adverb phrase or clause

An adverb phrase or clause tells when, where, how, why, or under what conditions the main action of the sentence occurred.

Example sentence with editing. Original sentence: When Irwin was ready to iron his cat tripped on the cord. Revised sentence: When Irwin was ready to iron, his cat tripped on the cord.

Without the comma, readers may have Irwin ironing his cat. The comma signals that his cat is the subject of a new clause, not part of the introductory one.

Example sentence with editing. Original sentence: Near a small stream at the bottom of the canyon the park rangers discovered an abandoned mine. Revised sentence: Near a small stream at the bottom of the canyon, the park rangers discovered an abandoned mine.

The comma tells readers that the introductory prepositional phrases have come to a close.

The comma may be omitted after a short adverb phrase if there is no danger of misreading.

Example sentence: In no time we were at 2,800 feet.

Comma with adjective phrases

Sentences can begin with participial phrases that function as adjectives, describing the noun or pronoun immediately following them. The comma tells readers that they are about to learn the identity of the person or thing described. Therefore the comma is usually necessary, even when the phrase is short.

Example sentence with editing. Original sentence: Buried under layers of younger rocks the earth's oldest rocks contain no fossils. Revised sentence: Buried under layers of younger rocks, the earth's oldest rocks contain no fossils.

Example sentence with editing. Original sentence: Thinking his entrance into St. Peter's Square was routine Pope John Paul II smiled and waved at the crowds. Revised sentence: Thinking his entrance into St. Peter's Square was routine, Pope John Paul II smiled and waved at the crowds.

Exercises:

Major uses of the comma 1

Major uses of the comma 2

All uses of the comma