The colon (:) is one of my favourite forms of punctuation in the English language. In a sense, this is because it always serves as a threshold or introduction to information that complements the previous sentence. It also acts as a convenient bridge to bulleted items, quotation marks, and small but relevant details that expand or amplify the content of the previous sentence. It is important to remember that, formally, you should use colons only after complete sentences; furthermore, the colon is always substitutable by the words "namely," or "that is"; so, if "namely" or "that is" fits perfectly at the end of the first part of your sentence, so will the colon. It is important to remember that the colon is a pause before introducing more elements relating to the previous sentence. Let us take an example. You want to describe your experience skydiving today, so you write,
"I felt so many emotions while plummeting to earth from the wing strut of an airplane today."
That is a sentence on its own, but if you want to elaborate, you write,
"I experienced so many sensations when I was plummeting to earth from the wing strut of an airplane today: exhilaration, fear, and absolute wonder."
In this case, the colon lays out the red carpet for more information about skydiving. And notice that the colon can be substituted by the word "namely." Of course, the colon would not work if your sentence was incomplete; for instance,
"When I am plummeting to earth from the wing strut of an airplane:"
That is not a sentence, so Mr. Colon has no right to be there!
Introducing the next visitor
In the book, Punctuate It Right (which I discovered while reading Grammar Girl), the author calls the colon a mark of expectation. I regard it as the messenger of the King's court, blowing his trumpet as a signal announcing the arrival of an important visitor. Although those "visitors" might only be a basket of groceries or camping accessories, their introduction is important and, in the context of the colon, neat and presentable.
"I bought some interesting things for my trip to the bush today: a lion-proof tent, some sedatives, and a satellite phone in case we are surrounded by elephants and need to be evacuated by helicopter."
Notice again, that you can substitute "namely" for the colon.
To cap or not to cap
A common confusion that results from the use of the colon is when to capitalize the first word following a colon and when not to. When a single independent clause follows a sentence, you don't need to capitalize the first word following the colon (unless it is a Proper noun). For example,
"I experienced many sensations plummeting to earth without a parachute today: loathing, fear, dread, and panic."
However, when you use two or more sentences after a colon you would capitalize the first letter of the first words starting each sentence. For example,
"Three thoughts went through my mind as I was plummeting to earth without a parachute today: First, what is my family going to do without me? Second, what will I look like when I hit the ground? Third, why did I take up parachuting in the first place?"
Emphasizing a point
An understated attribute of the colon is its usefulness in adding emphasis to a point made in the opening sentence. This is illustrated by the following sentences, where the second part of each sentence is clearly the one that needs emphasis.
"If you are scuba diving 40 meters under the ocean and you start panicking, it is essential to remember three things: stop, breathe, and look around."
"The doctor was clear in his message about his patient's obesity: if you continue overeating, you will die."
Colons and quotations
Colons are also very useful as precursors to quotations. When introducing a quotation, such as "He said," "She stated," or "The Minster intoned" the common practice in US English is to use a comma. For example,
He said, "I am going to Starbucks today,"
She said, "I discovered an archaeological ruin today."
However, a colon can be used when preceded by an independent clause, one that serves as a sentence on its own. For example, the first part of the following sentence is an independent clause, so a colon would follow it.
Responding to the judge's question in court, the accused stammered: "I don't remember, M'Lord."
However, if the sentence was transposed and started with a quotation then the quotation would always be closed with a comma, for example,
"I don't remember," the accused stammered,
Colons and lists
Colons are also popular in introducing vertical lists or bulleted items. A typical example would be the following:
The research article made three important findings regarding risk factors facing the US population:
- Heart disease kills about 610,000 people every year
- Cancer claims the lives of 592,000 Americans every year; and
- Lower respiratory disease claims 147,000 American lives annually
It is important to remember that a colon should always follow text introducing bulleted or otherwise listed items. There has been much discussion around whether to capitalize bulleted items after a colon. The rule of thumb is this: If the text following the bullet forms a complete sentence, it should begin with a capital letter; lowercase can be used if it does not, but often this rule is flexible according to the author or relevant style book's preference. Technically, a period should be placed at the end of a bulleted phrase or sentence, but this rule is flexible and is also at the author's discretion. When using bullets in association with colons, the bulleted items should ideally be kept short for more impact and easy reading. Elaboration of such bulleted items can be made in subsequent paragraphs.
Spacing after colons
A question often asked in using colons is the number of spaces that should be placed after a colon. The short answer is one. In the days of typewriters, two spaces were used, but now one is standard around the world.
Dashes
Some writers seem to prefer using dashes instead of colons. For example,
"The skier recorded the fastest time in the event—25 minutes and three seconds."
A colon can just as easily be used in this context, and often the author's personal choice wins the day here. However, it is important to remember that a colon can never be used to introduce a phrase unrelated to the first part of the sentence. For example,
"Mrs. Jones brought a long list of items at Walmart: thinking of the housework."
That, of course would have to be,
"Mrs. Jones brought a long list of items at Walmart: oranges, pears, lentils, rice, potatoes, and assorted cookware. Afterwards she went home."
In the first sentence, the second independent clause is not related to the first; in the second example, it is.
Multiple other uses of the colon
Colons also serve an important role in the English language as separators in references and book titles, in the use of times, and to separate main titles from subsidiary titles. Here are a few book titles examples:
"On the Campaign Trail: A politician's personal odyssey to the White House."
"Hatha Yoga: A handbook for personal change."
Colons are also used in bibliographies and references to separate cities and publishers. They are also used in ratios, particularly mathematical ratios, in model building, and in equations, where they are often used to denote a ratio, such as "10:1" (ten to one). The colon is also often used in business letter addresses, and, in US English, to separate hours and minutes.
Abbreviated lists
While the general rule is to use a colon only after a sentence, there is flexibility in the sense that people using abbreviated lists may use a colon after just one or two words. For instance, in an agenda for a business meeting, a colon may be used after the time and a single/double word description. For example,
9 am: Introductory speech: State of the Economy
10 am: Discussion: History and Future Trends
11 am: Closing speech: Acknowledging hosts.
In the above example, the colon facilitates the brevity of the meeting's format and serves as a perfect bridge between the time, the subject (not a full sentence), and the following phrase. Similarly, to accentuate items on an itinerary, a travel organizer may write:
Monday, October 10: Beijing; Tuesday October 11: New Delhi; Wednesday, October 12, New York.
Essential rules
Some useful rules to follow when using colons are: Do not use a list following a verb or preposition. For example, you would not say,
"I can play: the flute, the guitar, and bagpipes."
You would rather say,
"I can play the flute, the guitar, and bagpipes."
Some people make the mistake of using a colon after a preposition. A typical example would be,
"The dinner consisted of: a main course and a dessert."
Rather, you would say,
"The dinner consisted of a main course and dessert."
Another important rule is never to use a colon after the words "include," "including," or "included." For example, you would not write:
"The flowers I saw during my walk today included: hyacinths, roses, and poppies."
Instead, you would say,
"The flowers I saw during my walk today included hyacinths, roses, and poppies."
Another important rule to consider is that a colon may be used instead of a semicolon to separate two independent clauses, when both clauses are sentences in their own right. For example,
"The law is very clear on this matter: throw stones at your neighbor's greenhouse, and you will go to jail."
Some purists argue that when the second clause forms a sentence, then the first letter of that sentence should be capitalized… e.g., "Throw stones…" However, there is flexibility in the English language and whether to capitalize depends on the author's preference (mine would be lower case). Another rule is that if a quote is followed by two or more sentences, a colon would be preferable. For example,
The tycoon said: "Work until you can work no more. Focus on the goals you wish to achieve. Be honest at all times."
In academic writing, a colon is often used to introduce long tracts of information or long quotations. In these instances, the text following the colon is usually indented half an inch on the left and right margins. Here's an example:
Dylan Thomas, the author of Under Milkwood, started his book with the following paragraph:
To begin at the beginning:
It is Spring, moonless night in the small town, starless and bible-black, the cobblestreets silent and the hunched, courters'-and- rabbits' wood limping invisible down to the sloeblack, slow, black, crowblack, fishingboat-bobbing sea. The houses are blind as moles (though moles see fine to-night in the snouting, velvet dingles) or blind as Captain Cat there in the muffled middle by the pump and the town clock, the shops in mourning, the Welfare Hall in widows' weeds. And all the people of the lulled and dumbfound town are sleeping now.
To summarise, the colon is an excellent bridge-building punctuation mark that serves both as a threshold to further elaboration of ideas or as a door that offers an opening to quotation marks, lists, bulleted items, ratios, and references. It is easy to use and works to simplify even the most complex presentations or dissertations into incisive, easy-to-read prose.