Consider the colon: It is another device to alter emphasis in a sentence subtly. Starting with a not, it is not a semi-colon which is a device used in place of a period to separate independent clauses. “John went out to play baseball; he took his bat.” A semi-colon is used in lieu of two separate sentences because the thoughts are closely linked; although separate sentences would be grammatically proper.
A colon on the other hand introduces something that follows: a list or a statement are examples. It is almost always used after the word following. It is very close to the dash, and there are times when they might be used interchangeably, though a colon is thought to be more formal than a dash. It has apparently been a tool used much more by our British cousins, though its use seems to be rising here.
Should the first word after a colon be capitalized? Not if what follows is less than a complete sentence. We finally settled on the following colors: green for the bedroom, blue for the kitchen, and red for the dining room. (There’s a house you would not want to live in!) Only three members attended the meeting: the president, the secretary, and the treasurer. We know when to expect him to explode in anger: when his ears flushed red.
In all three illustrations what follows the colon is less than a full sentence; the first two contain lists of nouns without verbs, and the last contains a dependent clause (i.e., the clause after the colon has a verb, but it is not a complete thought).
Where a complete sentence follows the colon, it is proper to capitalize. The president gave the treasurer who embezzled the funds two choices: He could either resign and reimburse the company, or he could risk criminal indictment. Know, though, that there are those who would not capitalize; it is optional but most would capitalize. If a dash were used in lieu of the colon, the following he would have a lowercase h.
Consider The president gave us a choice: Should we jail the treasurer or sue him civilly? Again, following the colon is a complete sentence but this illustrates the use of a question and a question mark. Note that the s in Should is capitalized.
Show restraint in the use of the colon; by its nature it causes even though slightly an interruption in the thought process of the reader. Given a choice between The women were distressed: It was the mens� rude behavior and It was the mens� rude behavior that caused the women to be distressed, the latter would be preferred since it eliminates the mental check imposed by the colon.
A final proscription: Do not separate a verb from its direct object with a colon. The tools the mechanics were told to carry included: a drill, a set of wrenches, and an electric saw. The same can be said of the object of a preposition. Smoking was permitted only in: the special room in the rear, a designated exterior area, and the basement. The preposition in should not be segregated from its objects, and the use of a colon there was improper.
Now, about that colonoscopy . . .
– Ken Butera