A Colon is a punctuation mark in English. It consists of two round dots, one above the other (although occasionally these are small squares).
The colon immediately follows the word before and there is a space between the colon and what follows.
Note that the colon is a very different punctuation mark to the semicolon and although they have similar names (because they look similar), they are not really related in their usage.
In the TESOL classroom you can explain how the colon is primarily used to introduce what follows and usually this is a list of items. This explanation will cover the majority of uses of the colon.
The most common English punctuation marks are: comma, semicolon, colon, period, exclamation mark and question mark.
In American English what follows the colon often begins with a capital letter, however in British English it is usually lower case (unless it's a proper noun or would normally begin with a capital).
Colons are used in several different ways in writing.
Colons are most commonly used after a statement to introduce a list. For example:
the following items were stolen by the removal company: a gold tin, a silver bracelet, a set of brass scales...
only a few states have nuclear weapons: the USA, Russia, the UK, France, China, India, Pakistan, North Korea and Israel.
Sometimes if we want to give emphasis, we can introduce just a single item with a colon:
Guess what he was wearing: nothing!
There is just one rule of fight club: you don't talk about fight club.
Colons can be used to introduce quotations:
As Bertrand Russell said: "Men are born ignorant, not stupid. They are made stupid by education."
And although direct speech is usually introduced by a comma, sometimes you can also use a colon, especially if what is said is not just part of the conversation but more of an emphasized quotation or something which will be quoted later on. Notice how only the final piece of direct speech is introduced by a colon, the earlier examples are introduced by commas:
Lady Marcia turned to me and asked, "Have you got the time please?"
"Sorry," I said, "But I don't wear a watch."
Lady Marcia gave me a withering look: "Servants wear watches; a gentleman carries a timepiece."
Colons can also be used to explain the previous statement:
I'm cold: the boiler isn't working.
She arrived late: the train was delayed.
Finally, colons are used to introduce examples. You'll have noticed that we've used them a lot on this page (and also throughout all the TESOL resources on this site).
In writing, the colon is also used in special cases such as the following:
1) Biblical citations to show Chapter and Verse
"I permit no woman to teach or have authority over men; she is to keep silent." (Timothy 2:11)
"For every one that curseth his father or his mother shall be surely put to death: he hath cursed his father or his mother; his blood shall be upon him." (Leviticus 20:9)
The meeting will commence at 13:30 and conclude at 14:45.
Note that British English will more commonly use a full stop (or period):
The meeting will commence at 13.30 and conclude at 14.45.
The ratio of male to female Oscar winning directors is 65:1.
Although you can sometimes see a colon used after a salutation in a formal letter, it's more common to use a comma:
Dear Mr Smith:
Thank you for your letter of 16th August...
The word colon comes from the Latin, colon which itself comes from the Ancient Greek kolon (κῶλον) meaning limb or member. There is evidence that the colon was used before Ancient Greek, but it appears not have been used as the Greeks (and now modern English) used it.
William Caxton (the first printer of English) used a colon in 1474 to mark distinct pauses in a sentence.
By 1600 some printers used it to mark a pause or separation in writing which was less definitive than a period but stronger than a semicolon. Meanwhile at the same time other printers used the colon, comma and period almost interchangeably. The grammarian Justin Brenan wrote at the time that a dash should be used instead of a colon which he disliked, however the colon could not be killed off.
Note that the word colon referring to the intestine has a different etymology and Ancient Greek root and is not related to the word colon used in punctuation.