This reference page gives brief explanations for the proper use of punctuation.
Commas ,
Colons :
Use a comma to separate words or word groups in a series.
Example:
The Criminal justice system includes cops, courts, and corrections.
When two or more adjectives precede a noun, use a comma between the adjectives.
Example:
The six unnamed federal agents conducted an illegal, unwarranted search.
Use a comma to separate independent clauses that are joined by the coordinating conjunction: and, but, or, nor, for, so, or yet.
Example:
He searched, and she read them their rights.Example: (use a semicolon for independent clauses with no coordinating conjunction)
He searched; she read them their rights.
Use a comma to separate introductory clauses, introductory participial phrases, and long introductory prepositional phrases from the rest of the sentence.
Example:
When the police went on strike, citizen fear of crime rose.Example:
At the edge of the crime scene, uniformed officers kept the crowd back.Example:
Because they worked hard, the Detective Bureau cleared the case.Example:
The Detective Bureau cleared the case because they worked hard.
Use a comma to separate short introductory elements from the rest of the sentence. Such elements may be: yes, no, well, why, still, or now.
Example:
Still, the reporter distorted the facts.
In general, use a comma with any introductory expression that would be followed by a pause if you were speaking.
Example:
I like hamburgers, not donuts.Example:
Police discounts are fifty percent, not ten percent.
Use paired commas with nouns of direct address when they interrupt a sentence.
Example:
Tell the court where, Officer Jones, did you first see the defendant?
Use paired commas with transitional or parenthetical expressions that interrupt the sentence.
Example:
Tell the court, in your own words, where you first saw the defendant.
Use a colon to separate a list of items from an introductory statement, which often contains the words as follows, the following, these, or a number. Never use a colon after a verb.
Example:
The following were named in the suit: the warden, the deputy warden, and the corrections officers involved.
Use a colon to separate an introductory statement from an explanation or a long quotation.
Example (explanation):
I agree: donuts are brain food.Example (long quotation):
Masur summarized it best: "[W]hen we say that something is the law, what we mean is that we predict that a court, if faced with a specific question, will rule in a certain way" (1999).
Use a colon after the salutation of a business letter.
Example:
To the Citizen Review Board:
Use a colon to separate hour and minutes in numeric expressions of time.
Example:
The subject was apprehended at 20:42 hours on June 6, 1999.
Use a semi-colon to join two grammatically complete sentences that continue a thought. Semi-colons allow the writer to avoid short staccato sentences.
Example (without semi-colon):
The subject entered the house. The officer followed.Example (with semi-colon):
The subject entered the house; the officer followed.
Use semi-colons before conjunctive adverbs (e.g., therefore, however) when joining two sentences. Note: the conjunctive adverb must be followed by a comma.
Example:
My client is innocent; however, he might consider a plea bargain.
Use a semi-colon to seperate items containing commas in a list.
Example:
Your client attempted to purchase narcotics from the undercover officer on Friday, June 5th; Saturday, June 6th; and Sunday, June 7th.
Use quotation marks to enclose a speaker's exact words. Always place commas and periods inside closing quotation marks.
Example:
"You have the right to remain silent. You have the right to an attorney." The officer informed them.
Place colons and semicolons outside closing quotation marks.
Example:
The victim said, "he's over there"; unfortunately, there was no one in sight.
Place question marks and exclamation points inside closing question marks if just the quotation is a question or an exclamation. Place the marks outside the closing quotation marks if the whole sentence is a question or an exclamation.
Example:
"What's your prisoner number?" said the corrections officer. I said "tell me your prisoner number"!
Use quotation marks to enclose the titles of short stories, essays, short poems, songs, individual television and radio programs, magazine articles, and parts of a book.
Example:
I was on one episode of "Cops."
Use quotation marks to enclose nicknames and slang expressions.
Example:
Corrections officers are called worse than "screws" by inmates.
Use single quotation marks to enclose a direct quotation or title that occurs inside another quotation.
Example:
I asked the sergeant and he told me "the Captain said 'no' to your raise."
Use an apostrophe to show that letters have been omitted from contractions.
Example:
The Caprice can't touch the Mustang as an interceptor.
Use an apostrophe to show that the first two numbers have been omitted from a year.
Example:
The '95 Mustang was the best.
Use an apostrophe to form the plural of letters and numbers. The apostrophe is not needed when making centuries and decades plural: 1880s and 1400s.
Example:
That kid painted a bunch of ten's on the wall before he saw us.
Use an apostrophe and an 's' to make a singular noun possessive.
Example:
A prisoner's property is restricted to items from the prison store.
To show possession, add an apostrophe and an 's' to a plural noun that does not end in 's.'
Example:
The patrolmen's oaths to uphold the law were questioned by Reverend Sharpton.
When a plural noun ends in 's,' add only an apostrophe to show possession.
Example:
The officers' resented the implication that they were a danger to the community that they served.
The possessive forms of personal pronouns do not have apostrophes.
"Its" describes the property owned by it. "It's" is a contraction for "it is."