The grammatical colon is not to be confused with the anatomical colon.
All-l-l-l-l-l righty, then.
The colon has three main functions:
1. to introduce identifications,
2. to introduce examples, and
3. to introduce quotations.
The colon separates two units; the second unit expands on the first. The first unit is a sentence or clause, which sets up the second unit. the second unit is a quotation, or a list, or an identification of the first unit.
1. Identification: second unit identifies what the first unit is talking about.
A. Today they face a further treat to their survival: starvation.
B. There are numerous variables that can contribute toward an increasing totalitarianism within a new religious movement: one obvious one is physical isolation.
2. Examples: when phrases such as for example, as follows, namely, and for instance are not used, a colon is used.
A. There were three reasons for his failure: laziness, ill health, and lack of training.
(If the verb of the first unit directly precedes the list, no colon is used. Ex: The three reasons for his failure were laziness, ill health, and lack of training.)
B. To install the application:
1. Put the OED2 CD in the CD drive.
2. Run Windows.
3. Double-click on the program file SETUP.EXE.
4. Follow the instructions on the screen.
3. Quotations: a colon is used to introduce a long or formal quotation. Direct quotations after a colon begin with a capital letter.
A. The goal was clearly stated: "[T]o discover an architectural form that can accommodate all these functions at once."
B. One broker said: "Even as late as yesterday, I suppose the market had a 90% belief in war."
Source: The Oxford English Grammar, by Sidney Greenbaum, 1st Ed.; The Elements of Grammar, by Margaret Shertzer, 1st Ed.
OK, we covered the three main functions. There are lesser functions. To wit:
4. After a formal salutation in a business letter: Gentlemen: To Whom It May Concern: Dear Madam:
5. To separate a title from a subtitle: Jazz Lives: Portraits in Words and Pictures
6. Preceding the restatement of an idea: The sentence was poorly constructed: it lacked both unity and coherence.
7. Separating hours and minutes: 2:30
8. In biblical references, separating chapter from verse: Genesis 11:1-9
9. Separating units of a ratio: 2:1 3:1:1
10. In some abbreviated forms, to separate the heading from the accompanying information.
PS: I forgot to mention that . . . .
Admission: Members $5, Guests $7
1st Prize: . . . .
Note: Punctuation varies for items in a list; questions should end with question marks. For example:
Before you leave on a long road trip, ask yourself:
1. Have you packed everything you need?
2. Do you have emergency road supplies?
3. Have you had the car checked?
If the list isn't a group of questions, you may use a period after each list item, or a period after the last item only, or no punctuation at all. Formal business documents use a semi-colon after each item, and a period after the last item.
Source: The Oxford English Grammar, by Sidney Greenbaum, 1st Ed.; The Elements of Grammar, by Margaret Shertzer, 1st Ed.
Woman in front of a whiteboard briefly explains colon usage.
Source: YouTube
I always thought the semi-colon was easier than a colon, because it's basically used to separate clauses in a compound sentence, if there's no conjunction there. (Otherwise, use a comma.) There are variations on that theme, but that's the bottom line. Here are some variations:
1. A. If there is no coordinating conjunction between the clauses of a compound sentence, put a semi-colon there. EX: Johnny whistled and ran after the bus; the bus driver still didn't stop.
1.B. Also, in "A," if there is a quoted word or phrase just before the next clause, then the semi-colon comes after the quotation. EX: The bus driver's name was "Lawrence"; he preferred "Larry."
2. If any of the clauses themselves have commas in them, put a semi-colon between the clauses. (Makes it easier to read, instead of having commas everywhere.) EX: Johnny whistled and ran after the bus; but the bus driver not only didn't stop, he sped up.
3. If you have three or more clauses with no conjunctions, that is likely a list, and the clauses are separated by semi-colons. EX: We are a nation of softies: we ride instead of walking; we take an elevator instead of the stairs; we spend our free time in front of a television or computer.
4. Situation: You have two clauses. The second one is dependent (doesn't make sense without the first), and there's a conjunctive (connecting) adverb, like consequently, therefore, however, also, moreover, and so on. Put a semi-colon before the connecting adverb (and a comma after it). EX: Johnny saw the bus coming; however, he made no attempt to run to the bus stop.
5. If you have a name with a title (like a job title: Frank Jones, CEO), then the name will be separated from the job title by a comma. But if you have a list of names and titles, the name-title combinations are separated by semi-colons. Think about it: without the semi-colons, you'd have commas all over, and you'd have a hard time figuring out which name goes with which title. EX: The newly-elected student council officers were: Johnny, president; Judy, vice-president; Jimmy, secretary; and Jessica, treasurer.
6. In a footnote or bibliography reference, where you have a series of book or article names, authors, and page numbers, use a semi-colon between each reference. EX: Hart, American History Told by Contemporaries, 2nd Ed., pp. 493-499, 523-530; and Elson, History of the United States, 3d Ed., pp. 101-114.
5. If a list when the list is preceded by introductory phrases such as for example, for instance, to wit, i.e., and so forth, then put a semi-colon before the phrase. EX: Johnny didn't have any of his athletic gear with him; that is, neither his shoulder pads, his cleats, his helmet, nor his brain. (NOTE: the list may or may not be in sentence form.)
Source: The Oxford English Grammar, by Sidney Greenbaum, 1st Ed.; The Elements of Grammar, by Margaret Shertzer, 1st Ed.
The ubiquitous Paige Carrera explains the use of a semi-colon when two clauses are joined by a conjunctive adverb, such as HOWEVER or THEREFORE. Relates to #4 in the preceding text explanation.
Source: YouTube