Punctuation
The Comma, Period, Semi-Colon, Colon, and Dash
The Comma
In general, don't use a comma unless you have a reason for it. Commas are used to help your reader to understand what you are trying to say, by separating or setting off a part of a sentence.
"Rules" about comma use vary from place to place and from style book to style book. The seven rules outlined here, which should stand you in good stead for academic and other kinds of writing.
1. Separate Two Independent Clauses
Use a comma to separate two independent clauses when they are joined by for, and, nor, but, or, yet, or so ("fanboys"). An independent clause is a group of words that can stand alone as a sentence.
What I say can make a difference, but what I write can change the world.
Canadians could ask that the CBC be abolished, or they could choose to support it.
If the two clauses are really short, fewer than about five words, the commas can be omitted.
Bakers sell bread and greengrocers sell produce.
2. Separate Items in a Series
Rowboats, canoes, kayaks, and other motorless watercraft are welcome. [Comma before 'and']
Rowboats, canoes, kayaks and other motorless watercraft are welcome. [No comma before 'and']
Putting a comma before the "and" that indicates the last item in the series is optional. This comma is called the Oxford comma or the serial comma. Note that the use of the serial comma is recommended in The Publication Manual of the American Psychological Association (6th ed.).
Dates and Addresses
When including a date or an address in your sentence, treat it as a series, and put a comma after every item, even the last:
He was born on May 17, 1957, in London, England, and grew up there.
When you are writing only the month and year, the comma can be omitted.
In September 2010 she moved to Nova Scotia.
Lengthy Series
Often semi-colons are used to separate complex or lengthy items in a series.
3.Separate an introductory element from rest of the sentence
This element can be a word, phrase, or subordinate clause. Learn more about subordinate clauses.
However, cookbooks predating the 19th century are scarce.
By the turn of the century, the more advanced cookbooks showed evidence of the interest in domestic science.
Because refrigerated freight cars made the transportation of produce possible, Canadian cuisine became more varied.
4. Around an expression
Put commas around an expression such as however, moreover, therefore, of course, I think, indeed, etc., that interrupts a sentence midway through. These expressions are considered extraneous to primary meaning of the sentence.
I think, however, that you are wrong.
She thought, moreover, that you would agree with her.
The early Canadian attitude toward skating, nevertheless, upheld traditional beliefs about women in this era.
5. Around non-essential modifiers
Put commas around non-essential modifiers, also known as non-restrictive modifiers. This rule is related to rule 4 above, but rather than referring to expressions of one or two words, it deals with longer material. In a sentence, a non-essential or non-restrictive modifier may be interesting, but the primary meaning of the sentence would be clear without it.
John Wayne, whom I liked immensely, died in 1990.
"Whom I liked immensely" is not essential to the primary meaning of the sentence. Without it, the sentence would read:
John Wayne died in 1990.
Therefore, the non-essential material or restrictive modifier is set off from the rest of the sentence by commas to show that it could be left out.
Restrictive modifiers
There are also restrictive modifiers, which may look like non-restrictive modifiers but are not.
Women who chose to wear bloomers were accused of wanting to be like men.
The modifier "who chose to wear bloomers" is essential to the primary meaning of the sentence. Without it, the sentence would read:
Women were accused of wanting to be like men.
This sentence sounds like all women were accused. The modifier "who chose to wear bloomers" is essential because it tells us which women the sentence is about. It is an essential or non-restrictive modifier and it is not set off from the rest of the sentence with commas.
Rule 5 Summary:
Non-essential or non-restrictive modifier = set off by commas:
My sister, who likes the cold, is spending a year working up north.
Essential or restrictive modifier = no commas:
My sister who likes the cold is spending a year working up north; my sister who doesn’t is planning to visit her in July.
6. Before a concluding element
Use a comma, if the concluding element is considered non-essential.
Fancy skating eventually emerged as an appropriate sport for women, allowing them to maintain a feminine image.
7. Around the name of a person spoken to or addressed
I think, Erin, that you are absolutely right.
This rarely, if ever, happens in academic writing, so this rule is more for your information than anything else. It might occur in a formal letter or email when you want to directly address the person to whom you are writing.
The Period (The Full Stop)
- End of a sentence
- Period after an Abbreviation
- Use a period after an abbreviation: when the abbreviation does not end with the last letter of the word: Jan. Nov. Mon. Weds.
- You do not need a period after an abbreviation when the abbreviation ends with the last letter of the word. So: Dr St (for street or saint) Ave
- However, many people find it easier to just think "abbreviation = period at the end of the word" and put periods after all abbreviations. This is also acceptable and common: Dr. St. Ave.
The Semicolon
- Between two independent clauses: Use a semicolon between two independent clauses when you want to join them together and make a compound sentence. Learn more about compound sentences.
- Example: The French made grave mistakes during this time; Moltke made many serious errors.
- Between Items in a Lengthy Series
- Example: Tourists avoided New York in the 1970s for several reasons: they considered it unclean; parts of the city, including a large section of the subway system, were unsafe; and accommodation at a reasonably comfortable hotel was very expensive.
The Colon
The colon directs the reader's attention to what follows. What can follow a colon is fairly wide-ranging:
- An Individual Item or Series of Items
- Example: The emergence of the paperback brought several changes to the publishing industry: sales increased, mass marketing became more important, and royalty regulations had to be altered.
- An Idea Contained in the Preceding Clause
- Example: Hardcovers are now very expensive: the average price of a hardcover novel is $34.95.
Usually there is an independent clause (complete sentence) before the colon. A common mistake is to use a colon to introduce a list when there is no complete sentence preceding it.
Incorrect: The paperback can be: carried easily, printed cheaply, and thrown away.
Correct: The paperback can be carried easily, printed cheaply, and thrown away.
Correct: The paperback has many advantages over the hardcover: it can be carried easily, printed cheaply, and thrown away.
The Dash
Use dashes sparingly in formal, academic writing. If another punctuation mark will do, use that.
- Sudden Shift in Direction: Sometimes, you may have a phrase which contradicts or negates what has gone before, and a dash is a useful way of drawing the reader's attention to that contradiction.
- Example: Teachers can win over their students with tactics of affection - or of terror.
- Question or exclamation in the middle of a sentence
- Example: Students dread these lectures - who would not? - but they attend every week.
Punctuating Quotations
1. In the Structure of a Sentence
If you work the quotation into the structure of your sentence, no introductory or additional punctuation is necessary.
Thoreau suggests the consequences of making ourselves slaves to progress when he says that "We do not ride on the railroad; it rides upon us."
2. Attributory Words
If you use attributory words, words that identify the speaker or the writer and a verb of saying (says, writes, observes, notes etc), use commas to set off these words, whether they appear before, after, or between parts of the quotation.
McKenzie reports, " The reproductive capacity of the blue whale was the lowest of all baleen species."
"The reproductive capacity of the blue whale," McKenzie reports, "was the lowest of all baleen species."
"The reproductive capacity of the blue whale was the lowest of all baleen species," McKenzie reports.
3. An Independent Clause Precedes the Quote
If you precede your quotation with an independent clause or complete sentence, use a colon to introduce the quotation.
Hedley Bull is quite clear on this point: "We are accustomed, in the modern world, to contrast war between states with peace between states, but the historical alternative to war between states was more ubiquitous violence."