Punctuation: Traffic Signals in a Sentence

Structural Punctuation in a Sentence

First, here is a little punctuation “quiz.”
(Just add punctuation and justify it.)
1. When I called Jane came running.
2. We moved to Liberty Missouri years ago.

3. My best friends Tom Dick and Harry enjoy my corny humor.
4. These are my best friends Tom Dick and Harry.
5. Here is why I like them they laugh at my jokes!  (Answers below)

Punctuation is not arbitrary! It makes sense because it makes a sentence flow. I have received a variety of interesting requests to address punctuation, especially the comma! What I want to present is a logical analysis of a sentence to show where punctuation fits— and where it does not. Here’s a practical tip: Listen to yourself. If you hear a pause, “feed it”—but, please, not always with a comma. 

Analyzing the Core Sentence
Instead of using grammatical language, let me begin with the simple idea of a Core: the essence of a sentence. When a set of words comprises a story—an actor and action; a subject and a predicate—we have a sentence. For example: John reads books. Sue reads slowly. The children are happy with their books.
Notice two features of these Core sentences:
1. As you read each basic Core sentence aloud, you do not pause; therefore, you have nothing to feed until the period.

2. At the end of a Core sentence, your voice falls. In contrast, here is a bunch of words where your voice would rise to indicate a lack of closure: After thinking about the problem for weeks and asking countless questions . . . . Clearly, this is not a story; in fact it is that awful monster, a fragment.

Punctuating Before the Core: the “Introductory ” 
It is quite appropriate to create a sentence with “attachments” to the Core. However, because the Core is the basic structure for meaning, any attachments must be indicated with punctuation!

Before the Core, a comma functions to convey the pause (as it did in this sentence). It may also serve to avoid temporary ambiguity, as in After I called Bill answered. (Actually, I did not call Bill—but that is what the sentence first seems to convey.)
After I called, Bill answered. (Now, the ambiguity is gone.)
Since the writer always knows what is intended and may not recognize an ambiguity, The Gregg Reference Manual suggests always using the introductory comma, even with very brief introductory elements. The Associated Press Stylebook disagrees and first wants the writer to first determine if there might be an ambiguity. But most of us don’t write for the press, so why not do it the easy way?

Punctuating Within the Core: “Inserts”
An insert is a group of words within the Core that provides useful information, but is not essential to the Core. An insert actually results in two audible breaks when read aloud and needs two pieces of matching punctuation to set it off: a pair of commas, a pair of parentheses, or a pair of em dashes.
1. My younger sister, who lives nearby, is a good friend.
2. Your book (in case you hadn’t noticed) is overdue.
3. Three very important people—my spouse, my best friend, and     my supervisor—will help me.
Some comments on my punctuation:
1. For the first sentence, a pair of commas works best because this is a simple insert, and there is no other internal punctuation. With an emphatic statement, I could also have used a pair of em dashes. (An em dash is two hyphens with no space on either side.)
2. For the second sentence, instead of a pair of parentheses, I could again have conveyed emphasis with a pair of em dashes. (Commas do not provide an adequate break here.)
3. For the third sentence, a pair of em dashes is necessary for two reasons: (a) Setting the series off with commas would create confusion because commas are already associated with the list. Tip: Never use commas at two levels at once.
(b) Parentheses convey material that is “parenthetical”—not so important. Clearly, that's actually contradictory here.

Further Explanation after the Core
Information after the Core has punch! Here’s what I mean: BAM! The end of the Core is a great place for a word or phrase, a series, or even an explanatory sentence. 

For a word or phrase following the Core, there are three punctuation options: a comma, a colon (my favorite), or an em dash.
 I have one important goal—survival! Compare that sentence with this one: Survival is my most important goal. (Clearly this second sentence lacks punch.)

For a series, there are only two punctuation options: a colon or an em dash. Using a comma to set off a series would truly be confusing. I like to think of the colon as a “Yoo hoo”: it is a clear signal that whatever follows the Core will point back to and elaborate on the Core itself. I really enjoy these three fruits: mangoes, passion fruit, and pineapple. An em dash also works here—if the statement is emphatic. 

For an explanatory sentence after the Core sentence, a colon serves best: It clearly conveys that the second Core explains the first. I have one request: please come early. An em dash here would convey emphasis, but otherwise, it looks too casual. Although a semicolon is grammatically correct between the two sentences, it fails to convey that the second Core explains the first, and thus a semicolon is not helpful here. (More in a later posting.) 

Answers: Remember, it is not enough to be right, you need to know why!

1. When I called, Jane came running. (an introductory to avoid ambiguity)
2. We moved to Liberty, Missouri, ten years ago. (an insert—hear the pause?)
3. My best friends—Tom, Dick, and Harry—enjoy my corny humor. (an insert)
4. These are my best friends: Tom, Dick, and Harry.     
    (an explanation after the Core)
5. Here is why I like them: they laugh at my jokes!
    (an explanation after the Core)