Commas have many uses; some of these include after introductory elements, between items in a series, between independent clauses connected by a coordinating conjunction, and with non-restrictive elements.

After introductory elements:
Use a comma after most introductory elements, such as prepositional phrases, dependent clauses, and some single words.

Dependent Clause: Because of our lead in the market, we may be able to risk introducing a new product.

Prepositional Phrase: Through more careful planning, we may be able to serve more people.

Single Word: Meanwhile, George worked on the written report.

When the introductory prepositional phrase or word is short, you may omit the comma:

Thus we may not need to hire anyone.

Items in a series:

Another use for the comma is between items in a series of three or more. Company style may dictate omitting the final comma, but if you have a choice, use the final comma; doing so can often lessen the chances of misunderstanding.

I brought a pencil, a scantron, and a dictionary to the test.

Between independent clauses separated by a coordinating conjunction (for, and, nor, but, or, yet, so):

She spoke to the sales staff, and he spoke to the production staff.

You may eliminate the comma when the independent clauses are very short.

Non-restrictive elements:

A non-restrictive element, which can be a clause, a phrase, or a single word, contains extra information that is not essential to the sentence; it should be set-off with commas.

Non-restrictive clause:

A restrictive element is one that cannot be omitted without altering the meaning of the main clause; it should not be set off with commas.

Restrictive clause: The website that is produced by Steve Conley has won several design awards. [No commas are used before and after that is produced by Steve Conley because this information is necessary to the meaning of the sentence, as it specifies which website.]

Appositives:

Another use for paired commas is to set off appositive words and phrases. An a appositive further describes or defines what precedes it. Like non-restrictive clauses, appositives can be dropped without changing or obscuring the meaning of the sentence.

Appositive: Conley, a freelance designer, also produces the websites for several nonprofit corporations.

Between coordinate adjectives:

Commas are used between adjectives modifying the same noun (coordinate adjectives).

She left Monday for a long, difficult recruiting trip.

To test the appropriateness of such a comma, try reversing the order of the adjectives: a difficult, long recruiting trip. If the order cannot be reversed, leave out the comma (a good old friend isn't the same as an old good friend).

Use the colon after the salutation in a business letter. You should also use a colon at the end of a sentence or phrase introducing a list or (sometimes) a quotation.

Our study included the three most critical problems: insufficient capital, incompetent management, and inappropriate location.

A colon should not be used when the list, quotation, or idea is a direct object of the verb or preposition. This rule applies whether the list is set off or run in.

Another way you can use a colon is to separate the main clause and another sentence element when the second explains, illustrates, or amplifies the first.

Management was unprepared for the union representatives' demands: this fact alone accounts for their arguing well into the night.

Use a semicolon to separate two closely related independent clauses.

The outline for the report is due within a week; the report itself is due at the end of the month.

A semicolon should also be used instead of a comma when the items in a series have commas within them.

Our previous meetings were on November 11, 2006; February 20, 2007; and April 28, 2008.

Use a semicolon to separate independent clauses when the second one begins with a conjunctive adverb such as however, therefore, or nevertheless or a phrase such as for example or in that case.

Our supplier has been out of part D712 for 10 weeks; however, we have found another source that can ship the part right away.

With possessive nouns (except possessive pronouns):

A noun becomes possessive when it is used to show the ownership of something. Then you add 's to the word.

the man's car the woman's apartment

However, ownership doesn't need to be legal.

the secretary's desk the company's assets

Also, ownership may be nothing more than an automatic association.

a day's work the job's prestige

An exception to the rule about adding 's to make a noun possessive occurs when the word is singular and already has two "s" sounds at the end. In cases like the following, an apostrophe is all that's needed.

crisis' dimensions Mr. Moses' application

When the noun has only one "s" sound at the end, however, retain the 's.

Chris's book Carolyn Nuss's office

To form the possessive of plural nouns, just begin by following the same rule as with singular nouns: add 's. However, if the plural noun already ends in an s (as most do), drop the one you've added, leaving only the apostrophe.

the clients' complaints employees' benefits

With contractions (missing letters):

Use an apostrophe in place of the missing letter(s) of a contraction.

we will, we'll

do not, don't

they are, they're

Subject/Verb

Every verb must agree in number with its subject, both in person (first, second, or third) and in number (singular or plural).

In a simple sentence, making a verb agree with its subject is a straightforward task: Hector Ruiz is a strong competitor.

Confusion sometimes arises when sentences are a bit more complicated. For example, be sure to avoid agreement problems when words come between the subject and verb. In the following examples, the subject and verb are underlined.

The analysis of existing documents takes a full week.

Even though documents is a plural, the verb is in the singular form because the subject of the sentence is analysis, a singular noun.

The answers for this exercise are in the study guide.

Either/or and Neither/nor: When either/or or neither/nor are used in a sentence, the verb should agree with the noun closest to it.

Neither Bill nor his parents work in the store on Sundays.

Parents (plural) is the noun closest to the verb work, so the verb is plural as well.

With the words number or variety: To decide whether to use a singular or plural verb with subjects such as number and variety, follow this simple rule: If the subject is preceded by a, use a plural verb.

A number of products are being displayed at the trade show.

If the subject is preceded by the, use a singular verb.

The variety of products on display is mind-boggling.

Pronoun/Antecedent

Like nouns, pronouns can be singular or plural. Pronouns must agree in number with their antecedents (the word the pronoun refers back to): a singular antecedent requires a singular pronoun.

The president of the board tendered his resignation. [his is the pronoun referring back to the antecedent president.]

Multiple antecedents require a plural pronoun.

The members of the board tendered their resignations. [their (plural) is the pronoun referring back to the antecedent members.]

A pronoun referring back to singular antecedents connected by oror nor should be singular.

Neither Sean nor Terry made his quota.

But a pronoun referring to a plural and a singular antecedent connected by or or nor should be plural

Neither Sean nor the twins made their quotas.

Run-ons occur when two or more independent clauses are joined with no connecting words or punctuation.

All our mail is run through a postage meter every afternoon someone picks it up.

To correct the error, find where the sentence should be separated and do one of the following:

Add a comma and a coordinating conjunction between the independent clauses.

All our mail is run through a postage meter, and every afternoon someone picks it up.

Or

All our mail is run through a postage meter every afternoon, and someone picks it up

Add a semicolon between the independent clauses and do not capitalize the next word (unless it's a proper noun).

All our mail is run through a postage meter; every afternoon someone picks it up.

Change one of the independent clauses so that it becomes a phrase or a dependent clause. This remedy often produces the best writing, but it takes more work.

After our mail is run through a postage meter, someone picks it up in the afternoon.

A comma splice occurs when the independent clauses are separated by a comma, which doesn't eliminate the problem. You could substitute the comma with a semicolon or make one of the suggested changes above to correct the error.

Modifiers are used to qualify the meaning of other parts of speech. They should be placed next to or as close as possible to the word, phrase, or clause they are meant to modify.

Some misplaced modifiers appear in the middle or toward the end of a sentence and create unclear and sometimes unintentionally humorous sentences.

Antia Information Systems has bought new computer chairs for the programmers with more comfortable seats.

Because the phrase with more comfortable seats is next to the noun programmers, it sounds as though the programmers have more comfortable seats, which is ridiculous.

Antia Information Systems has bought new computer chairs with more comfortable seats for the programmers.

Now the phrase is correctly modifying computer chairs.

Dangling modifiers usually occur toward the beginning of sentences and are said to be "dangling" inappropriately.

Lying motionless, co-workers rushed to Barry's aid.

Readers expect an introductory phrase to modify the subject of the main clause; however, in this case, it wasn't the co-workers who were lying motionless but rather Barry who was in this situation. Because of the placement of the phrase, it is inappropriately modifying co-workers and not Barry.

Pronouns change depending on their placement in a sentence. When pronouns appear in the subject position of a sentence or clause, they are called nominative. When they appear in the object position of a sentence or clause, they are called objective. Determining which pronoun to use in a sentence can be difficult. For example in the following sentence, which pronoun is correct?

James and (I, me) took the course together.

The correct pronoun is I because James and I are the subjects of the sentence, so the nominative case is used. Which is correct in the following sentence?

Dena went to the concert with Nancy and (I, me).

The correct pronoun is me because Nancy and me are the direct objects in the sentence, so the objective case is used.

A very simple way to determine the correct pronoun case is to remove the other person or persons from the sentence and say it the way you normally would. For example, take James out of the first sentence and say the sentence the way you normally would: I took the course. In other words, you would know not to say Me took the course. Then you can add James back into the sentence. It works with the second sentence as well: Dena went to the concert with me. You would not normally say Dena went to the concert with I. Now add Nancy back in: Dena went to the concert with Nancy and me.

Every writer sometimes wonders whether to use who or whom:

(Who, Whom) will you hire?

Because this sentence is a question, it's difficult to see that whom is the object of the verb hire. You can figure out which pronoun to use if you rearrange the question and temporarily try she and her in place of who and whom: Will you hire she? or Will you hire her? Her and whom are both objective pronouns, so the correct choice is Whom will you hire?

Two or more sentence elements that have the same relation to another element should be in the same form. Otherwise, the reader is forced to work harder to understand the meaning of the sentence. When a series consists of phrases or clauses, the same part of speech (preposition, gerund, etc.) should introduce them. Do not mix infinitives with participles or adjectives with nouns. Here are some examples of nonparallel elements:

Andersen is hiring managers, programmers, and people who work in accounting. [nouns not parallel]

Here is the corrected sentence: Andersen is hiring managers, programmers, and accountants.

Andersen's goals are to win new clients, keeping old clients happy, and finding new enterprises. [infinitive mixed with gerunds]

Here is the corrected sentence: Andersen's goals are to win new clients, keep old clients happy, and find new enterprises.

Many adjectives used in the business world are actually combinations of words: up-to-date report, last-minute effort, fifth-floor suite, well-built engine. These adjectives are hyphenated when they come before the noun they modify. However, when such word combinations come after the noun they modify, they are not hyphenated. In the following example, the adjectives appear in italics, and the nouns they modify are underlined:

The report is up to date because of our team's last-minute efforts.

Hyphens are not used when part of the combination is a word ending in ly (because that word is usually not an adjective). Hyphens are also omitted from word combinations that are used so frequently that readers are used to seeing the words together:

We live in a rapidly shrinking world.

Our highly motivated employees will be well paid.

Please consider renewing your credit card account.

Send those figures to our data processing department.

Our new intern is a high school student.