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Commas have three distinct functions:

(A) to separate members of the same category

(B) to set off elements

(C) to clarify meaning

A.  Separator Commas

The first type of commas, separator commas, is used to separate members of the same type; in other words, these commas are inserted between members of equal rank.


a.  Items in a Series

Separator commas are used to separate three or more items in a series:

(1) Macquardt, a sophomore, had a pair of doubles, six runs, six walks, and two RBI.

In (1), we have a series of items (pair of doubles, six runs, six walks, two RBI) separated with a comma.  The last comma before the conjunction and is optional.  If you are going to use separator commas to separate items in a series, you cannot use the coordinating conjunction unless it is used for the last item in the series; in (1) above, that last item is two RBI which is joined to the other items with the coordinating conjunction and and an optional separator comma.


b.  Coordinate Adjectives

Separator commas are also used with coordinate adjectives; coordinate adjectives are adjectives which could be joined with and:

(2) Her kind, gentle manners have made her a popular director.

In (2), kind and gentle are adjectives modifying the noun manners.  Since they are of the same type (adjectives), we can use a separator comma.  Alternatively, since these are coordinate adjectives, we can omit the comma and use the coordinating conjunction and to conjoin the two adjectives:

(3) Her engaging and encouraging manners have made her a popular director.

Only coordinate adjectives can be separated with commas.  To check if a sequence of adjectives is actually a sequence of coordinate adjectives, see if you can insert and between the adjectives; if that is possible, then these adjectives are, in fact, coordinate adjectives and can be separated by a separator comma.

Not all adjectives are coordinate adjectives; if a sequence of adjectives is not a sequence of coordinate adjectives, there should be no comma separating those adjectives.  For example, in the following sentence,

(4) She finally found the light blue sweater her mother had given her.

the adjectives light and blue are not coordinate adjectives since and cannot be inserted between them; therefore they should not be separated with a comma.

c.  State/Year
  Separator commas are also used to separate streets, cities and states from each other or to separate the different parts of a date.  For example, in (5)

(5) OSU plays a doubleheader Thursday, May 20, 1994, in SpokaneWashington.

Commas separate the day (Thursday) from the date (May 20) and the year (1994) as well as the city (Spokane) from the state (Washington).  Note that when the full date is given, as in (5)--Thursday, May 20, 1994-- the year is also followed by a comma.

d. Appositives 


Non-restrictive appositives (commenting appositives, that is) are set off with commas:

(6) Louis Sullivan, Secretary of Health and Human Services, defended the violence initiative before a meeting of psychiatrists.

In (6), Secretary of Health and Human Services is in apposition to Louis Sullivan.  It is non-restrictive because it provides additional but not crucial information on Louis Sullivan.  Since it is non-restrictive, then, the appositive is set off by commas.

e.  Separator Commas in Compound Sentences

 The separator comma is used between two independent clauses, creating a compound sentence.  For example, in the following compound sentence,

(7) The students measure the water's dissolved oxygen content, and they test for chemicals such as phosphates and nitrates.

the comma separates one independent clause (the students measure the water's dissolved oxygen content) from another independent clause (they test for chemicals such as phosphates and nitrates).
B.  Delimiter Commas

The second function of commas is to set off elements from the rest of a sentence; these commas (or comma) mark the limits of an element rather than being inserted between elements of the same category (as was the case with all the separator commas discussed above).

a.  Introductory Phrases

Introductory phrases are set off (separated) from the sentence with a comma:

(8) On a couple of pioneering campuses, bookstore computers generate letters to faculty members to advise them of discrepancies between orders and sales.

The introductory prepositional phrase, on a couple of pioneering campuses, is separated from the rest of the sentence with a comma.  Similarly, in the following sentences

(9) Considered in its entirety, the package of textbook materials is tangible proof that students have been presented with information essential for learning the material in question.


(10) Paradoxically, the very qualities that make professors impatient with traditional textbooks are precisely the things that could make them of greatest value to today's variously educated students.

The introductory material of both sentences --considered in its entirety and paradoxically, respectively--  is separated from the rest of the sentence with a comma.

If the introductory phrase is short (one or two words), the comma can be omitted:

(11) Today three out of five people over the age of 65 will require some form of long-term care in their lifetime.

b.  Parenthetical Modifiers

Parenthetical expressions often help with the rhythm of the sentence but do not add to the information (meaning) of the sentence.  Parentheticals must be separated with commas from the rest of the sentence.

(12) In his research, he says, he found many mixed-blood Indians acting as 'cultural brokers.'

In the following sentence a conjunctive adverb (nevertheless) serves as a parenthetical:

(13) Despite the arrival of new technologies, the textbook will be a staple of higher education for years to come; we should, nevertheless, think about what we could lose if all textbooks were suddenly to disappear.

Other expressions can serve as parentheticals, modifying the flow (rhythm) of the sentence:

(14) These loans, let me emphasize, are not the ones the states were anxious to make.



(15) No single answer is possible, of course, but the unexamined curriculum is not worth teaching.


(16) Mr. Friedman, meanwhile, will not discuss the matter.


c.  Non-restrictive Relative Clauses
Non-restrictive relative clauses simply provide additional--but not necessary--information to the noun, and, therefore, are set off with commas from the rest of the sentence.  For example, in the following sentence:

(17) Mr. Martin's performances, which have made him a local celebrity, have also allowed him to get some exposure for his own work.

The relative clause which have made him a local celebrity is non-restrictive because it is not absolutely necessary for understanding the meaning of the noun it modifies--performances.  Rather, it provides additional information.  Since, then, the relative clauses is non-restrictive, it is set off with commas.

d.   Introductory Dependent (Subordinate) Clauses

Delimiter commas are used to separate a dependent subordinate clause from an independent clause only if the dependent subordinate clause precedes the independent.

(18) Although experimentation with human embryos was banned for more than a decade under the Reagan and Bush Administrations, an advisory committee at the NIH is preparing to recommend that such research start up again.

The first part of sentence (18) is a dependent clause introduced with the subordinating conjunction although; since the dependent clause precedes the independent, it must be separated from the independent clause with a comma.

e.  Direct Address

In direct speech, we need to separate the name of the addressee from the rest of the sentence.
 (19) Could you please come over here, Alexander?

(20) And I'm asking you, ladies and gentlemen, is Orwell right when he complains that corrupt language can corrupt thought?

(21) Please listen to me, everyone.

f.  Direct Quotations

When we are quoting material, we must set it off with commas from the rest of the sentence.

(22) "Whatever happened in this situation is really something between the president and the dean," says Mr. Argenti.

If the quotation is discontinuous, as in the following sentence,

(23) "History departments today," he says, "aren't interested in politics, or wars, or heroes."

then a comma separates the first part of the quotation (history departments today) from the unquoted material (he says) and a comma separates the unquoted material from the second part of the quotation (aren't interested in politics, or wars, or heroes.)
 C.  Clarifying Comma
 Rarely, we need to insert a comma to break up a sequence of words which could lead to an unclear or even ambiguous reading of a sentence.

(24) Those who can, teach; others do research.

Omitting the comma after can will lead to misreading; therefore, we must insert a comma to avoid confusing the reader and to make our intended meaning clear.


A colon (:) is used to separate hours from minutes (5:30) or chapter from verses in the Bible (Genesis 3:6) or titles from subtitles (Language: An Introductory Textbook).  It is used to introduce lists; in this case, a clause must precede the colon:

(1) He decided to work on the following projects:  writing a paper, cleaning the garage, and mowing the lawn.

A colon is also used to introduce a quotation;

(2) Says Mr. Aronowitz:  "This is arrogant, but we are the pioneers of cultural studies in the United States.

A colon us used to connect two independent clauses, the second of which serves as an explanation or a summary of the first clause.  In other words, the colon makes the reader anticipate an explanation (thatís why itís often called Ďanticipatoryí).

(3) Our point is simple:  Political scientists must study legislators from both parties.

In such a case, you can insert namely after the colon:

(4) Our point is simple:  Namely, political scientists must study legislators from both parties.

Often, the word that follows the colon begins with a capital letter;  this, however, is not an absolute but a choice.

The dash is used to separate elements in a sentence; it is just the opposite of the hyphen (-) which is used to join words with each other.

The dash can be used to highlight an appositive:

(1) But those closest to the president--members of the search committee that hired him--describe him as a straight-forward scholar who enjoys intellectual debate.

It is necessary to use dashes around the appositive if it already includes commas:

(2) His favorite activities--swimming, running, and biking--took most of his time.

In general, the dash is used to draw the reader's attention to a particular element in the sentence that the writer wants to emphasize; as such, then, it is as much a rhetorical device as it is a punctuation mark:

(3) Oberlin's system--unlike many services on the Internet--can deliver high resolution photographs.

Finally, a dash is used to indicate a break in the rhythm of the sentence or to introduce an afterthought:

(4) I used to complain about the workload--but who wouldn't?


Hyphens are used to connect words with each other.  For example, if we want to connect words together and use them as adjectives, we must use a hyphen:

(1) The system lets him list up-to-the-minute information about alumni events.

In sentence (1), we used hyphens between the words up, to, the, and minute to create a phrase that functions as an adjective modifying information.

If the group of words is not used as an adjective preceding a noun, we don't need a hyphen.  For example, in sentence (2)

(2) My son is ten years old.

ten years old is not used as an adjective; therefore, no hyphens are needed.

On the other hand, in (3)

(3) My ten-year-old son is excited about his upcoming birthday.

the phrase ten-year-old functions as an adjective modifying son.  Therefore, we need to use hyphens between the individual words in the adjective phrase.

We also use hyphens for compound words, words formed by joining two words together:

(4) She is the secretary-treasurer for the organization.

The use of hyphens can actually change the meaning of a phrase.  Note, for example, the difference between the following phrases:

(5) two-gallon cans vs. (6) two gallon cans.

In (5), we have cans that can contain two gallons whereas in (6) we have two cans each containing one gallon.

We also use hyphens when we spell out fractions (two-thirds) and numbers (from twenty-one to ninety-nine).


A semicolon is similar to a period since it requires a clause; it differs from a period, however, in that it indicates close connection between clauses; in other words, the semicolon tells readers that the two clauses it connects have a close meaning relation.

We have seen semicolons being used in compound sentences, often in conjunction with conjunctive adverbs (also called adverbial conjunctions):

(1) The board members could not be reached for comment; however, Benita Budd, a spokeswoman for the university, said the members believe Mr. Sanchez had restructured the university too drastically.

Semicolons can be also used with items in a series (replacing commas) only if these items are long and have internal commas:

(2) There are catalogues of exhibitions that were mounted over the years; some 5,000 slides, primarily of artists' works; and some 200 films and videotapes.

Since one of the items on the list of sentence (2) above, namely some 5,000 slides, primarily of artists' works, includes a comma, it must be separated from the other items (catalogues--films and videotapes) by a semicolon.