This is “Using Commas Properly”, section 18.1 from the book Writers' Handbook (v. 1.0).
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Commas are to readers as road signs are to drivers. Just as a driver might take a wrong turn if a sign is missing or misplaced, a reader cannot traverse a sentence meaningfully when commas are not properly in place.
Commas set introductory words, phrases, and clauses apart from the rest of a sentence. This separation serves to signal a reader to pause and to give words a chance to have meaning without interference from other words.
Single-word example: Afterward, fans came backstage and surrounded the actors and actresses.
Phrase example: Without an invitation, fans swarmed backstage in excitement.
Clause example: After the fans began to head to their cars, the actors and actresses took their first break in two hours.
A series is a list embedded in a sentence with a conjunction, typically the word “and,” between the last two items in the list. Without the commas, a series can be quite confusing.
Series in a sentence without commas: Penny’s costume included a long blue dress a red bonnet black lace-up shoes a heavy gold pendant on a chain and a very-full petticoat.
With a little work, a reader can possibly identify the five items that made up Penny’s costume. But the sentence is confusing and requires too much work to read. Inserting commas makes reading this sentence very easy and clear.
Series in a sentence with commas: Penny’s costume included a long blue dress, a red bonnet, black lace-up shoes, a heavy gold pendant on a chain, and a very-full petticoat.
Some usage experts promote the idea that the comma immediately before the conjunction is optional since it has fallen out of universal use. However, it is still wise to use it to avoid inadvertent confusion.
When a sentence is made up of two independent clauses joined by a coordinating conjunctionA word used to link two independent clauses in a compound sentence (e.g., and, but, for, so, nor, or, yet); when used in this way, it is preceded by only a comma. (and, but, for, nor/or, so, yet), a comma is needed between the two clauses. Remember that an independent clause must have both a subject and a verb and be able to serve as a stand-alone sentence. (See Chapter 15 "Sentence Building", Section 15.1 "Incorporating Core Sentence Components (Avoiding Fragments)" for more on sentence components.)
Example of a compound sentence with two independent clauses: Mitch arrived an hour early for the first rehearsal, and he spent the time looking through the costume closets.
Example of a sentence with two clauses, one of which is not independent: Mitch arrived an hour early for the first rehearsal and spent the time looking through the costume closets.
To create interest and increase clarification, you may want to add words and phrases to basic sentences. These additional pieces often function as add-ons that are not essential to the core meaning of the sentence and do not change the meaning of the sentence. You should separate such words and phrases from the rest of the sentence. Some examples of nonessential wordsA word that is in a sentence but could be removed without changing the core meaning of the sentence. include adjective phrases and clauses, words of direct address, interjections, and appositives.
Some adjective phrases and clauses are essential to the meaning of a sentence and some are not. If they are essential, no comma is needed. If the meaning of the sentence would be intact if the phrase or clause were removed, a comma is needed. You can identify adjective clauses since they often begin with the relative pronouns where, when, which, who, whom, whose, or that.
Comma needed: To Kill a Mockingbird, which was Malik’s first play, lasted almost two hours.
A comma is needed because, even without the adjective phrase, the reader would know that the play lasted for two hours.
Commas not needed: Actors who give constant effort can inspire others in the cast to do well.
A comma is not needed because the phrase “who give constant efforts” clarifies which actors are being referenced within the sentence. Since the sentence meaning would not be complete without the phrase, no comma is needed.
Some sentences name the person being spoken to. A person’s name that is used in this way is called a noun in direct addressA noun that names the person being spoken to within a sentence.. Since naming the person does not change the meaning of the sentence, you should separate such a name from the rest of the sentence.
Your performance, Penny, was absolutely amazing!
Some words interrupt the flow of a sentence but do not actually change the meaning of the sentence. Such words are known as interjectionsA word that interrupts the flow of a sentence but does not actually change the meaning of the sentence. and should be set apart from the rest of the sentence with commas. Aside from “yes” and “no,” most interjections express a sudden emotion.
AppositivesA noun or noun phrase that restates an immediately preceding noun or noun phrase. are nouns or noun phrases that restate an immediately preceding noun or noun phrase.
Malik’s first play, To Kill a Mockingbird, had six performances.
Malik only has one “first” play, so the title of the play is a restatement of “Malik’s first play.” Since this sentence is complete with all meaning intact even if the words “To Kill a Mockingbird” were removed, the words need to be separated with commas.
My husband, Kyle, has visited the To Kill a Mockingbird museum in Monroeville.
Since “my husband” identifies a single person, the name “Kyle” merely restates his identity and thus adds no new information. Therefore, “Kyle” should be set apart with commas.
You should place a comma between coordinate adjectivesDouble adjectives that are not joined with the word “and” but that could be joined with the word “and” or could be rearranged and still work fine. that are not joined with the word “and.” Coordinate adjectives are double adjectives and can be joined with the word “and,” rearranged, or both and still work fine.
Sentence with coordinate adjectives: Atticus is a good role for Malik since Malik is a tall, stately guy.
This sentence requires commas since Malik could be “a stately, tall guy,” or he could be “tall and stately,” or he could be “stately and tall.”
Do not use commas between cumulative adjectives. Cumulative adjectivesConsecutive adjectives that build on each other in meaning. build on each other, modify the next one in line, and do not make sense if rearranged.
Sentence with cumulative adjectives: Atticus Finch is a dedicated defense attorney.
This is a cumulative adjective situation because it would not work to rearrange the adjectives to say “defense dedicated attorney” or “dedicated and defense attorney.” Therefore, no commas are needed in this example; the adjective “defense” modifies “attorney” and the adjective “dedicated” modifies “defense attorney.”
You should use a comma prior to or just after the quotations in dialogue. Also, use a comma before a direct quotationThe exact word or words spoken. when preceded by a verb such as declares, says, or writes.
Comma before dialogue: Jem said, “There goes the meanest man that ever took a breath of life.”
Comma after dialogue: “The one thing that doesn’t abide by majority rule is a person’s conscience,” said Atticus Finch.
No comma needed before or after a direct quotation that is not preceded by a verb: According to Miss Maudie Atkinson, Atticus “can make somebody’s will so airtight you can’t break it.”
No comma needed before or after an indirect quotation: Atticus told Jem that it was a sin to kill a mockingbird.
Details such as dates, addresses, geographic names, company names, letter and e-mail components, titles that go with names, and numbers all require commas when used in text and sometimes when used alone.
When a date is written in month–day–year order in isolation, you need to use a comma between the day and year.
December 25, 1962
When a date is written in month–day–year order within a sentence and does not fall at the end of the sentence, you need to use a comma between the day and year and between the year and the rest of the sentence.
On December 25, 1962, the movie To Kill a Mockingbird opened in theaters.
When an address is written in mailing format, commas are needed between the city and state.
Old Courthouse Museum
31 N. Alabama Ave.
Monroeville, AL 36460
When an address is written within running text, commas are needed between the city and state as well as between each of the “lines” of the address and between the address and the rest of the sentence if the address does not fall at the end of the sentence.
Annual performances of To Kill a Mockingbird are performed in the Old Courthouse Museum, Courthouse Square, 31 N. Alabama Ave., Monroeville, AL 36460, near where author Harper Lee grew up.
Use a comma after each item within a place name when the place name is used in running text, even when it is not part of a complete address.
Atticus Finch lived and worked in the fictitious city of Maycomb, Alabama, which many assume is patterned somewhat after Monroeville, Alabama, where the author grew up.
Company names that include “incorporated” or “limited” (or the like) require a comma between the name and “Inc.” or “Ltd.” only when a comma is placed there as part of the official company name. Check for letterhead or the company’s website for clarification on its preferred usage.
When “incorporated” or “limited” is part of a company name within a sentence, a comma is needed between the word and the rest of the sentence only when a comma precedes it.
Citigroup, Inc., is making some noise in the banking industry lately.
Invesco Ltd. started out slowly in that sector of the market.
Commas are used to separate letter and e-mail components both in isolation and within running text.
Use commas to set off descriptive titles that follow names. However, don’t use a comma before “Jr.” or “III” (or the like) unless you know the person prefers a comma.
Within text, include a comma both before and after the descriptive title to set it off from the whole sentence.
Atticus Finch, attorney-at-law, at your service.
In numbers with more than four digits, begin at the right and add a comma after every third digit. In a four-digit number, a comma is omitted in page and line numbers, addresses, and years, and it is optional in other cases. No commas are used in numbers with less than four digits. Numbers are treated exactly the same when used in text.
In an Internet search for “reviews of To Kill a Mockingbird,” 2,420,000 results surfaced.
Sometimes you simply have to use a comma to avoid confusion. For example, when a word is removed for effect, a comma can sometimes make up for the missing word.
To perform is a skill; to transform, art.
When two like or nearly like words are placed side by side, a comma can sometimes help clarify the intended meaning.
The whole cast came walking in, in full costume.
Sometimes you will need to use a comma so the reader understands how the words are to be grouped to attain the author’s desired meaning. Read the following example without the comma and note the difference.
Fans who can, come each year to see the annual To Kill a Mockingbird performance.
Add commas as needed to write each of these sentences correctly.