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Although most of the lessons in our English usage series thus far have focused on homonyms and homophones, after doing some keyword research earlier today I discovered that many of you have been searching for information on the correct usage of different kinds of punctuation marks. The correct use of apostrophes is one of the most popular, but since I have already covered this, we will move on to the next most popular in terms of search volume, which is “correct use of colon.”

It turns out that the colon actually has a significant number of uses, which I will describe below followed by an example of each. Afterward, I will briefly deal with other uses of the word colon that do not involve its use as a punctuation mark. The purpose of this is to clear up any confusion that readers may have about the word, also known as disambiguation.

• Deductive: the colon is placed before a logical consequence or effect that is deduced from something that happened before.
  1. After losing hundreds of dollars on AdWords, the newbie affiliate marketer finally realized his mistake: he was setting the bid amounts far too high in the beginning without doing the proper tracking to find out which keywords were actually converting into sales.
• Descriptive: the colon introduces items in a series or elements of a set.
  1. To carry out war, three things are necessary: money, money, and still more money. (Gian Giacomo Trivulzio, 1499)
• Appositive: A colon can be placed in between a noun and its appositive, a word or group of words that describes or renames the noun.
  1. One way to build a list is to use the ever-popular squeeze page: a simple opt-in form that displays some enticing text, collects a visitor’s name and email address, and usually includes a privacy policy stating that this information will not be shared with any third parties.
• Segmentation: The colon can introduce a direct speech or quote without actually using quotation marks.
  1. Albert Einstein once pointed out the significance of saving money: the most powerful force in the universe is compound interest.
• Introducing definitions:
  1. Libertarian: a person who believes in minimizing the use of force by governments while maximizing the freedom of individuals.
• Separation of titles and subtitles in movies, video games, and other such productions:
  1. Because of Akella’s unbelievable incompetence, the PC game Age of Pirates has been satirically renamed by forum members as Age of Bugs: Caribbean Bugtales.
• When writing the time of day, a colon is often used to separate the hours and minutes. A second colon may be used to separate the minutes and seconds if the latter item is included.
  1. The time 5:00 p.m. would be written as 17:00 in the 24-hour format.
• Separation of chapter and verse numbers in religious texts such as the Bible or Quran:
  1. John 3:16
  2. Sura 5:18
• In a formal letter, colons are used after the introductory greeting:
  1. Dear Sir or Madam:
     We regret to inform you that your application to our affiliate program has been rejected.
• In a memo or e-mail, colons are used after the introductory fields that are placed before the body text:
  1. From:
  2. To:
  3. Date:
  4. Subject:
• In mathematics, a colon is placed between two numbers to indicate a ratio. A similar usage of the colon occurs in cartography and model building where it is used between two number to indicate scaling.
  1. Traffic exchanges usually allow free members to earn credits at a ratio of around 2:1, which means that for every two pages you view in the rotator, you will receive one visit back to your site.
  2. If a model kit has a scale of 50:1 printed on the package, this means that the actual object is 50 times larger than the model will be after it has been assembled.
• In Internet chat jargon, colons may be combined with other symbols to form emoticons:
  1. If a colon is placed directly before a right parenthesis symbol, this indicates a smile. In WordPress blogs such as this one, this syntax is automatically converted into a smiley face icon like this:

Grammatically, the important rule to remember is that whatever you write before the colon is supposed to be an independent clause, meaning that it should be able to stand on its own as a complete sentence. If it does not, then you can either reword the sentence so that you have an independent clause before the colon or simply replace the colon with another punctuation mark such as a comma.

In terms of style and syntax, in modern usage a single space is placed after the colon but no spaces before it. This replaces the older convention of placing two spaces after colons and periods, which is what I was originally taught in typing class. After computers, the Internet, and word processors replaced typewriters, the second space became unnecessary.

Other meanings of colon:

• A part of the anatomy comprised of the large intestine. It is advisable to avoid developing cancer here if at all possible.
• A unit of currency in the countries of Costa Rica (CRC) and El Salvador (SVC).
• A city in the countries of Panama and Cuba (actually spelled Colón).