The 10 Key Rules of Punctuation

Though there aren't strict, unbreakable rules for punctuation, there are well-established style recommendations. Here is a compilation of the ten punctuation marks we use most frequently, along with a guide on how to use them.

10. The Comma

Commas are used to separate independent clauses in a sentence. For instance:

The match had ended, but the audience wouldn't leave.

It was her brother's birthday yesterday, so she treated him to dinner.

Place a comma after introductory words, phrases, or clauses that precede the main clause:

As I was eating, the cat scratched at the door.

If you're feeling unwell, you should visit a doctor.

NOTE: Reversing this order is not correct. For example, the following two scenarios are incorrect:

The cat scratched at the door, while I was eating.

If you're unwell, you should see a doctor.

Introductory words that should be followed by a comma include: yes, however, and well. For instance: Yes, you can attend the party.

Use a pair of commas to set off an aside from the main sentence. For example:

John and Inga, the neighbors from next door, are joining us for dinner this evening.

You can verify this by removing the aside from the sentence. If the sentence still makes sense, you've likely used the commas correctly. For example, the sentence would become: John and Inga are joining us for dinner this evening.

Do not use commas to separate essential parts of the sentence. For instance:

Students who cheat only damage their own futures.

The baby in the yellow jumpsuit is my niece.

The Oxford Comma

I prefer using the Oxford comma when creating lists. It's also called the Serial Comma or the Harvard Comma. The Oxford comma is more commonly used in American English compared to British English. When it's used, every item in a list of three or more elements is separated by a comma. For instance:

I enjoy apples, pears, and oranges.

Notice the comma placed after “pears”. Some people choose not to use this style and leave out the final comma. It's called the Oxford comma because it's the preferred method taught at Oxford University.

Commas should be used to separate all geographical names, elements in dates (except for the day and month), addresses (excluding the street number and name), and titles in names.

Birmingham, Alabama, takes its name from Birmingham, England.

July 22, 1959, marked a significant day in his life.

Sometimes, you'll notice a comma placed between the house number and street. While this is considered old-fashioned, it is not technically incorrect. It's simply not common in modern usage.

Use a comma to separate the main narrative from a quotation.

John said flatly, “I’ll see you tomorrow.”

“I was able,” she replied, “to finish the assignment.”

Use commas when they help avoid confusion:

To George, Harrison had been a kind of idol.

The main purpose of a period is to mark the end of a sentence. Its secondary role is for abbreviations. There are stylistic variations in this usage, and I will address both aspects.

Fowler

Martin Fowler, the author of Modern English Usage, suggests that we should add a period at the end of an abbreviation only when the last letter of the abbreviation differs from the last letter of the full word. For instance:

Jesus Christ was born c. 4-6AD

The abbreviation represents the word “circa” – since it ends in an 'a' and the abbreviation is typically ‘c’, the period is included.

Mr Jones was pleased to see his wife

St Patrick resided in Ireland

In the example above, “Mr” is short for mister. Since mister ends with an ‘r’ and the abbreviation contains that ‘r’, no period is necessary.

Other

Another situation where a period is used with abbreviations is when it's included regardless of whether the last letter of the word is part of the abbreviation.

Mr. Jones was delighted to see his wife

When an abbreviation is pronounced as a word, periods are not used. For example, NASA is correct, while N.A.S.A. is incorrect. In some cases, even if the word isn't pronounced, periods are dropped, particularly for terms that are widely known. One such case is UCLA (University of California, Los Angeles).

In the case of the phrase et cetera (etc.), we always include the period.

The question mark is a straightforward punctuation mark with a singular purpose. It is placed at the end of a sentence when it is posing a question. For instance:

How many people will be attending the party?

You should never use a period alongside a question mark. Additionally, while some may use a combination of question marks and exclamation marks in informal contexts, especially online, this is generally not acceptable in formal writing.

One important rule is to avoid using a question mark when it is unnecessary:

INCORRECT: I wonder how many people will attend the party?

While you're posing a question that seems to demand an answer, you're actually presenting it as a statement. This is a common error when using the question mark.

Use the exclamation mark exclusively to convey strong emotions or give commands! Just like with the question mark, avoid following it with a period, and do not combine it with other punctuation marks. Also, a single exclamation mark suffices; using two or three in a row is unnecessary.

Quotation marks are used to directly cite someone else's words, whether spoken or written. For instance:

John said, “We are going shopping.” – notice that “We” is capitalized. This is the standard unless you're quoting as part of a run-on sentence:

John said “we are going shopping” because they had no milk. Notice the lack of a comma in this example as well.

When quoting someone who is also quoting another individual, use single quotation marks like this:

John said, “My neighbor yelled at me today! He shouted ‘get off my lawn!’”

To introduce a quotation following an independent clause, use a colon rather than a comma:

As D. H. Nachas points out, “The gestures used to greet others vary significantly across cultures.” (This is not an independent clause.)

D. H. Nachas explains cultural differences in greetings: “Touching is not a universal sign of greeting.” (This is an independent clause.)

Quotation marks can also be used to indicate sarcasm, irony, or to highlight something peculiar about a term:

The great march of “progress” has resulted in millions living in poverty and hunger.

Punctuation and Quotation Marks

Punctuation that is part of the quoted material should be placed inside the quotation marks, while punctuation pertaining to the whole sentence should be placed outside.

Philip asked, “Do you need this book?”

Does Dr. Lim frequently tell her students, “You must put in more effort”?

Colons and semicolons should always be placed outside of quotes, while commas and periods should be placed inside quotes unless they are followed by parentheses.

He remarked, “I might forget your name, but your face will never escape my memory.”

Mullen, critiquing the lack of action, notes, “Donahue’s approach was to do nothing” (27).

A colon is used after a full statement to introduce related ideas, such as a sequence of instructions, a list, or a quote or explanation that supports or clarifies the statement. For example:

The newspaper is divided into four sections: news, sports, entertainment, and classified ads.

The methods of corporatist industrial unionism have proven ineffective: compromises and concessions have placed labor in a weaker position in the new “flexible” economy.

The colon is also used to separate chapters and verses in the Bible (I Parlipomenon 12:30), to separate hours, minutes, and seconds: 13:49:08, and as the eyes in smiley faces.

A semicolon is used to connect related independent clauses within compound sentences. For example:

Jim put in great effort to earn his degree; as a result, he was sure to receive a distinction.

Jane slept in for three hours; as a result, she was going to be late for work once more.

The semicolon is also used to separate items in a series when the elements within the series already contain commas. For example:

Band members include Harold Rostein, clarinetist; Tony Aluppo, tuba player; and Lee Jefferson, trumpeter.

The apostrophe serves three primary functions:

1) to indicate possessives of nouns 2) to show missing letters 3) to mark certain plurals of lowercase letters.

Forming Possessives

the boy’s hat

three day’s journey

If the noun following “of” refers to a building, object, or piece of furniture, an apostrophe is not necessary. For example: The car door.

Indicating Omission

He’ll go = He will go

could’ve = could have (Not “could of”!)

Creating Plurals

Apostrophes are employed to indicate the plural form of lowercase letters. For instance:

Pay attention to your p’s and q’s

Parentheses are occasionally used for supplementary, non-crucial information within a sentence. For example, they might enclose dates, references, or ideas that are secondary or not central to the main point. Parentheses always appear in pairs.

Just before reaching the station, the aged train (which some claimed was a remnant from frontier days) suddenly caught fire.

Dash

Dashes are used to highlight a point or to introduce an additional explanatory comment, but be careful not to use them too frequently, or their effect will diminish. On a computer, a dash is typically shown by typing two hyphens with no spaces before, after, or in between them.

To some, my ideas might appear radical–even revolutionary.

It is also applied when an appositive phrase already contains commas.

The boys–Jim, John, and Jeff–left the gathering early.

As you can observe, the dash can serve the same function as parentheses.

Hyphen

A hyphen should be used to link two or more words that function together as a single adjective before a noun.

chocolate-covered peanuts

Avoid using a hyphen when the noun appears first.

The peanuts are chocolate covered

A hyphen is necessary when writing compound numbers, such as Forty-five.

To prevent any confusion, it's essential to use a hyphen in certain sentences.

He had to re-sign the contract He had to resign his job

Hyphens should be used with prefixes such as ex- (for former), self-, and all-; with the suffix -elect; between a prefix and a capital letter; as well as with numbers or letters:

ex-husband self-assured mid-September all-inclusive mayor-elect anti-American T-shirt pre-Civil War mid-1980s

Content sourced under fair use from the Purdue University Online Writing Lab