Commas get a bad rap. Commas are commonly seen as the most difficult of all the punctuation marks to place, and grammar checking software stats show a majority of errors are related to comma use. To be fair to those of us that make these errors, commas seem to do a lot of things and have many rules. While comma rules can be complicated, commas simply do one thing:
Commas separate words, phrases, and clauses.
Think of them as the opposite of conjunctions--instead of bringing things together, commas cast thing apart. In Old English, comma use was surprisingly easy, as commas were the only punctuation mark that showed separation. Commas came between every clause no matter what, they offset subtitles and all list items, and they delineated unneeded information. Yet as syntax and English became more complex, we developed more nuanced punctuation marks. Take the following sentence, where the only punctuation mark that separates is a comma: At 4,55 in the recording, the senator clearly refers to his campaign stops in Des Moines, Iowa, Memphis, Tennessee, and Grand Rapids, Michigan, a comment that Dr. Morgan says in his book, "proves that the candidate is lying, as he did not set foot in those cities until the following month," 34.
That sentence, with its eleven commas, demonstrates why other punctuation marks developed. Colons were developed to show that two things were separate and related at the same time, like the minutes and second of time (4:55). Semicolons were developed to help separate items in a list where those items themselves had commas-- by writing the list Des Moines, Iowa; Memphis, Tennessee; and Grand Rapids, Michigan, the writer clarifies that the senator is speaking of three places, not six. Parentheticals and dashes were developed to show whether the separated information is essential (dash) or nonessential (parenthesis and brackets). With modern punctuation, the sentence terms are clearer: At 4:55 in the recording, the senator clearly refers to his campaign stops in Des Moines, Iowa; Memphis, Tennessee; and Grand Rapids, Michigan--a comment that Dr. Morgan says in his book, "proves that the candidate is lying, as he did not set foot in those cities until the following month" (34).
Of course, while these other punctuation marks are specialized to do very specific tasks, commas are relegated to taking care of every other kind of separation, leading to the common confusion of exactly what commas do and when they are needed. The following are the various types of commas and what they do in a sentence.
That sentence, with its eleven commas, demonstrates why other punctuation marks developed. Colons were developed to show that two things were separate and related at the same time, like the minutes and second of time (4:55). Semicolons were developed to help separate items in a list where those items themselves had commas-- by writing the list Des Moines, Iowa; Memphis, Tennessee; and Grand Rapids, Michigan, the writer clarifies that the senator is speaking of three places, not six. Parentheticals and dashes were developed to show whether the separated information is essential (dash) or nonessential (parenthesis and brackets). With modern punctuation, the sentence terms are clearer: At 4:55 in the recording, the senator clearly refers to his campaign stops in Des Moines, Iowa; Memphis, Tennessee; and Grand Rapids, Michigan--a comment that Dr. Morgan says in his book, "proves that the candidate is lying, as he did not set foot in those cities until the following month" (34).
Of course, while these other punctuation marks are specialized to do very specific tasks, commas are relegated to taking care of every other kind of separation, leading to the common confusion of exactly what commas do and when they are needed. The following are the various types of commas and what they do in a sentence.
SERIAL COMMAS (including Oxford)
Serial commas separate items in a list. A comma should follow every item in a list except the last one (I need to buy apples, bread, cinnamon, and pasta).
The serial comma before the coordinating conjunction is called the Oxford comma or Harvard comma and is not used by some style guides. MLA requires the Oxford comma as it leads to grater clarity. In the sentence My heroes are my parents, Batman and George Washington, the comma use implies that Batman and George Washington are the speaker's parents. Using the Oxford comma (My heroes are my parents, Batman, and George Washington) corrects this error.
Additionally, if the list items contain commas, they are instead separated by semicolons: I have dated Johnny, the quarterback of the football team; Norwood, the senior class president; and Ronnie, the only male cheerleader on the squad.
The serial comma before the coordinating conjunction is called the Oxford comma or Harvard comma and is not used by some style guides. MLA requires the Oxford comma as it leads to grater clarity. In the sentence My heroes are my parents, Batman and George Washington, the comma use implies that Batman and George Washington are the speaker's parents. Using the Oxford comma (My heroes are my parents, Batman, and George Washington) corrects this error.
Additionally, if the list items contain commas, they are instead separated by semicolons: I have dated Johnny, the quarterback of the football team; Norwood, the senior class president; and Ronnie, the only male cheerleader on the squad.
VOCATIVE COMMAS
Vocative commas separate interjections and nouns of direct address from the rest of the sentence. Remember that these words have no direct syntactic connection to the sentence subject, verbs, or complements: the vocative comma is placed to demonstrate that the interjection or noun of direct address is not connected. The comma occurs whether the word is at the start of the sentence (Hey, did you get the pie?) or at the end of the sentence (I can't believe you forgot the pie, bro!).
MULTIMOD (MULTIPLE MODIFIER) COMMAS
Multimod commas separate two adjectives that describe the same qualities of an object but do not separate different qualities.
How does this work? Adjectives that precede the noun are put in the following order: article/number opinion size age shape color origin material purpose. Here is an example, and notice that it has no commas: The plans called for an impressive sky-high modern rectangular grey German concrete sixty-story skyscraper.
Yet if I changed the sentence to The plans called for a modern, state-of-the-art sixty-story skyscraper, I need a multimod comma between modern and state of the art, as both are age adjectives. The sentence I bought two thick, solid posts also needs a multimod comma, as solid and thick are both size adjectives. Click the link for more details on modifiers and their commas.
How does this work? Adjectives that precede the noun are put in the following order: article/number opinion size age shape color origin material purpose. Here is an example, and notice that it has no commas: The plans called for an impressive sky-high modern rectangular grey German concrete sixty-story skyscraper.
Yet if I changed the sentence to The plans called for a modern, state-of-the-art sixty-story skyscraper, I need a multimod comma between modern and state of the art, as both are age adjectives. The sentence I bought two thick, solid posts also needs a multimod comma, as solid and thick are both size adjectives. Click the link for more details on modifiers and their commas.
MOVEMOD (MOVED MODIFIER) COMMAS
While adjectives must precede the word they modify (except in the case of predicate adjectives), adverbs can appear almost anywhere in a sentence. If an adverb is not either immediately before or after the word they modify, they need a movemod comma. Here's an example: Alarmingly, Mike found the bloody knife in his trunk. Alarmingly modifies found, but since it is not beside it, the word gets a comma. This can also happen at the end of the sentence (Mike was charged with Vanessa's murder, unfortunately) as well as in the middle of the sentence (Mike realized that his arrest, surprisingly, was on his birthday).
Adverbs are not always just single words: prepositional phrases are also adverbial or adjectival by nature. These phrases are supposed to follow the words they modify, as in the sentence We'll play Madden after eating some ice cream; no comma is needed in the sentence since the prepositional phrase follows the word it modifies (play). However, movemod commas are needed if the phrase is moved before the word it modifies: After eating some ice cream, we'll play Madden. Note that this is also true for participle and infinitive phrases.
Adverbs are not always just single words: prepositional phrases are also adverbial or adjectival by nature. These phrases are supposed to follow the words they modify, as in the sentence We'll play Madden after eating some ice cream; no comma is needed in the sentence since the prepositional phrase follows the word it modifies (play). However, movemod commas are needed if the phrase is moved before the word it modifies: After eating some ice cream, we'll play Madden. Note that this is also true for participle and infinitive phrases.
CLAUSAL COMMAS: loose and balanced
Clausal commas separate clauses. While all clauses used to be separated by commas, modern usage only separates clauses with a comma for periodic sentences (where a dependent clause is followed by an independent clause) and balanced sentences (where there are multiple independent clauses).
Loose commas (also called periodic commas) exist in periodic sentences and follow the dependent clause. In the sentence Once I murder the countess, I will inherit the Carlyle Diamond, a comma must follow the word countess to show that the independent (and thus most important) clause is to follow.
Balanced commas sometimes exist in balanced sentences between the independent clauses. Balanced sentences are tricky, as each independent clause has equal weight and needs an equalizer. There are four equalizers and each is used in a different situation:
Cumulative sentences (where dependent clauses follow independent clauses) don't need clausal commas. Neither do noun clauses or restrictive relative clauses (My boss that wears the ugly dresses founded the company). However, nonrestrictive relative clauses do need commas (My boss, who founded the company, wear the ugliest dresses to work). For more information on clauses, click the link below.
Loose commas (also called periodic commas) exist in periodic sentences and follow the dependent clause. In the sentence Once I murder the countess, I will inherit the Carlyle Diamond, a comma must follow the word countess to show that the independent (and thus most important) clause is to follow.
Balanced commas sometimes exist in balanced sentences between the independent clauses. Balanced sentences are tricky, as each independent clause has equal weight and needs an equalizer. There are four equalizers and each is used in a different situation:
- When the author wants to show a specific relationship between the clauses, a coordinating conjunction joins the two clauses. The balanced comma precedes the coordinating conjunction (I hate football, but I still watch it with Dad every Sunday).
- If the second clause is closely related to the first but has an independent meaning, they are joined by a semicolon (I have been a Broncos fan from birth; I was literally raised in a blue-and-orange onesie.")
- If the meaning of the second clause is unclear without the first, they are joined by a colon (I have made my peace with football: I let it play in the background and cheer when told to.")
- If the second clause breaks to a different topic from the first, they are joined by a dash (I'm such a football nut--say, did you ever throw around the ol' pigskin in high school?")
Cumulative sentences (where dependent clauses follow independent clauses) don't need clausal commas. Neither do noun clauses or restrictive relative clauses (My boss that wears the ugly dresses founded the company). However, nonrestrictive relative clauses do need commas (My boss, who founded the company, wear the ugliest dresses to work). For more information on clauses, click the link below.
APPOSITIVE COMMAS
Appositives are nouns that immediately follow and rename another noun. A common error is putting commas around a single appositive: My dog, Smuckers, likes to play fetch. This is unneeded, as the appositive needs no separation from the word it renames, which is why My dog Smuckers likes to play fetch is correct.
However, there are such things as appositive commas. Appositive commas are used for appositive phrases, which occur when an appositive has modifiers other than an article; since an appositive is grammatically equal to the word it renames in all aspects, the commas are needed to isolate the modifiers to just one subject. For example, no commas are needed for My brother the clown likes to scare children. However, appositive commas are used for My brother, the overweight redheaded circus clown, likes to scare children.
However, there are such things as appositive commas. Appositive commas are used for appositive phrases, which occur when an appositive has modifiers other than an article; since an appositive is grammatically equal to the word it renames in all aspects, the commas are needed to isolate the modifiers to just one subject. For example, no commas are needed for My brother the clown likes to scare children. However, appositive commas are used for My brother, the overweight redheaded circus clown, likes to scare children.
CONJUNCTIVE ADVERBIAL COMMAS
Conjunctive adverbs are always separated from the rest of the sentence by commas when at the start of a sentences (Moreover, these trends can be seen in the native populations) or in the middle of a sentence (When surveying the population, however, the results were surprising). However, be mindful that conjunctive adverbs modify the entire sentence to create a smooth transition (Additionally, the results from the latest survey show an overall sharp downturn in support); if the word only describes a single word, it is just a regular adverb and may not need a comma (The results from the latest survey additionally show an overall sharp downturn in support). This is also why i.e. (id est, Latin for that is) and e.g. (exempli gratia, Latin for for example) are followed by commas, as they are both conjunctive adverbs. Click the link for more information on conjunctive adverbs.
QUOTATIONAL COMMAS
Quotational commas separate the author or narrator's voice from the voices of others that are speaking of dialogue or giving a direct quote. Quotation marks alone are not enough as "some" quotation marks do not demonstrate "dialogue" per se, but are for emphasis. If the author's voice is before the quotation, the comma goes after the author's words: On page 13, Stevens claims, "No other scientist has found causality in this case." If the quotation comes before the authors words, the comma goes after the quotation but within the quotation marks: "I can't believe Monica word that," Jill said with a sneer.
Note that if the quotation is truncated to be part of a restrictive relative clause, the comma is ignored: Before the murder, Norman tells Marion that she "eats like a bird." For more on punctuating quotes, click the link.
Note that if the quotation is truncated to be part of a restrictive relative clause, the comma is ignored: Before the murder, Norman tells Marion that she "eats like a bird." For more on punctuating quotes, click the link.
NUMERICAL COMMAS
Comma separate every three digits in a number (3,468,972,601). When spelling out numbers fully, commas go in the same places: Three billion, four hundred sixty-eight million, nine hundred seventy-two thousand, six hundred and one. For more on numbers in writing, click the link.
GEOGRAPHICAL COMMAS
Geographical commas separate locations from the most specific location to the most general location. Typically the order is specific room, room or apartment number, building name, address, city, county, state, country, planet, galaxy: Mr. Coon's classroom, E100, Frederick High School, 5690 Tipple Pkwy, Frederick, Weld, Colorado, United States, Earth, Milky Way. Notice that zoning codes like ZIP codes are not part of this list, which is why there is no comma between a places and ZIP codes.
CHRONICAL COMMAS
Chronical commas divide units of time when they are out of order from smallest increment to largest increment. When listed as time day date month year, no commas are used-- 11:15 AM Thursday 14 September 2003; this is typically the way time is written in European countries. In the Americas, we write dates as day, month date, year, time and require commas-- Thursday, September 14, 2003, 11:15 AM. Chronical commas also divide units of elapsed time (e.g., four hours, thirteen minutes, and fifty-five seconds)
NOMINAL COMMAS
Nominal commas separate names from important titles that are usually linked with a name like Dr. John Frink, PhD or Mary DePalma, Esquire. While the same was once true for legacy names like Kurt Vonnegut Jr. or Thurston Howell III, commas are no longer used.
ELLIPTICAL COMMAS
Elliptical commas are used when leaving out a word in the second set of a parallel phrase or clause for stylistic effect, like in the sentence His pressed shirt was white; his tie, bright orange (the comma replaces the second was).