You might be surprised to learn that the colon is one of the most helpful and easiest to use of all the punctuation marks. You dont need to remember six or seven rules to understand how a colon works. In prose, a colon really does only one thing: it introduces. It can introduce just about anything: a word, a phrase, a sentence, a quotation, or a list. Youll notice that weve used colons in the two preceding sentences to introduce a sentence, in the first case, and a list, in the second case. This is how simple the colon is. Lets look at some other examples:
Joe has only one thing on his mind: profit.
We have used a colon in these four sentences to introduce various kinds of things: a word, a phrase, a sentence, and a list. You can use a colon in your prose in any place where you must directly introduce something. A colon gives special emphasis to whatever youre introducing because readers must first come to a stop, and so they pay more attention to it. For example, lets say you are writing a letter describing a product, and you want to emphasize above all that this product, the Jacobsen lawn mower, is reliable. You could very well write:
The Jacobsen lawn mower beats its competitors especially in the key area of reliability.
While this sentence gets the point across, it doesnt place much emphasis on reliability. A sentence using a colon is much more emphatic:
The Jacobsen lawn mower beats its competitors especially in one key area: reliability.
Notice that the second example places clear emphasis on the point that the writer is trying to communicate to his or her reader: that the Jacobsen lawn mower is above all reliable. The writer of this sentence has used the colon effectively.
Perhaps the most common way to use a colon is to introduce a list of items, as in this sentence:
This report reviews five main criteria to determine whether to purchase the IBM PC: hardware, software, maintenance agreements, service, and customer support.
If you arent sure whether you need a colon in a particular sentence, here is a handy test: read the sentence, and when you reach the colon, substitute the word namely; if the sentence reads through smoothly, then theres a good chance that you do need a colon. For example, you can read any of the example sentences above with the word namely in the place of the colon:
Joe has only one thing on his mind [namely] profit.
This test may not work 100 percent of the time, but it is a fairly reliable indicator of whether you need a colon.
One word of caution: do not place the colon after the verb in a sentence, even when you are introducing something, because the verb itself introduces and the colon would be redundant. For example, you would not write:
My three favorite friends are: Evelyn, Marlyne, and Ronni.
The colon is not necessary in the sentence above because the verb does the work of introducing the three friends. You can check this sentence by using the test we just mentioned. It would seem awkward to read this sentence, My three favorite friends are, namely, Evelyn, Marlyne, and Ronni. The fact that the sentence is awkward when you read it with namely is an indication that the colon is unnecessary. Remember, the colon shows emphasis and, therefore, you want the reader to stop at the colon before preceding on to whatever it is you are introducing.