The comma is the most frequently used punctuation mark in English and the one that provides the most difficulties to writers. Its most common uses are to separate items in a series and to set off or distinguish grammatical elements within sentences.

Between Main Clauses

1. A comma separates main clauses joined by a coordinating conjunction, such as and, but, or, nor, or so.

   She knew very little about the new system, and he volunteered nothing.

   The trial lasted for nine months, but the jury took only four hours to reach its verdict.

   We will not respond to any more questions on that topic this afternoon, nor will we respond to similar questions in the future.

   All the first-floor windows were barred, so he had clambered up onto the fire escape.

1. Missing commas or extra commas

    Incorrect: Avoid commas, that are not necessary.

    Correct: Avoid commas that are not necessary.

Have you ever been advised to “add commas where you would take a breath”? Sometimes this advice works—but sometimes it doesn’t. It’s especially dangerous when you’ve gone over and over your writing. At that point, nothing looks correct. To avoid confusion and frustration, don’t wing it.

1. Use quotation marks to set off a speaker’s exact words.

• “Did you eat the entire bag of chips?” Debbie squealed.

2. Use quotation marks to set off the titles of short works such as poems, essays, songs, short stories, and magazine articles.

• “The Lottery” by Shirley Jackson (short story)
• “Self-Reliance” by Ralph Waldo Emerson (essay)
• “We’ve Only Just Begun” by the Carpenters (song)

A semicolon is a comma and period combined, like this (;). The semicolon’s structure shows you that the semicolon is a hybrid of a comma and a period. It’s a stronger stop than a comma but not as strong as a period.however, nevertheless, moreover, for example,  and  consequently.

1. Use a semicolon between closely related independent clauses when the coordinating conjunction has been left out.

• The chef cooked far too much chicken; we eagerly devoured the excess.

2. Use a semicolon between main clauses connected by conjunctive adverbs such as 

• Sarah wanted to be a doctor; however, she faints at the sight of blood.

3. Use a semicolon to join independent clauses when one or both clauses contain a comma.

• Glenn, who is an accomplished musician, wanted to perform at his sister’s wedding; but he quickly discovered that Marcia, the maid of honor, had other plans for the entertainment.

Dashes are used widely in informal notes and letters.

(1) A dash can be used to attach an afterthought:

• I should love to come – that’s if I can get the time off.

(2) A dash can replace a colon before a list in informal writing:

• The thieves took everything – video, television, cassettes, computer, camera, the lot.