What is a Semicolon?

Punctuating Two Cores in One Sentence

Here’s an assertion I encountered when working on my dissertation: Adults rarely use semicolons incorrectly; in fact, they rarely use semicolons! (Still, I have observed some wonderfully creative uses.) However, I am not proposing a greatly increased use of semicolons. What I am suggesting is that there are places where they are useful and places where they are incorrect. You just oughta know which is which—and what your other options are!

Semicolons serve to separate two Cores in one sentence. We’ll get there, but first let’s just consider how and why we might put two Cores together in the first place when they could be two separate sentences:

1. They are logically related.
2. The are parallel.
3. They are short. 

Punctuation Options for Two Cores in One Sentence

1. Cores can be connected with a comma plus and, or, but:
I like coffee, and she likes tea. I like coffee, but she does not.
Notice that the only pause is after coffee. (We’d never pause after but.) And if you know these are coordinate conjunctions, you probably don’t need to read this!

2. Cores can be connected with a semicolon: a “soft period.” This means the Cores, again, could be separate sentences. So, the semicolon requires a Core on each side.
I like coffee; she prefers tea.
Dark chocolate is not just better; it is better for you. Incidentally, don't use a semicolon with and, or, but (except as indicated in # 6 below).

3. Cores can be connected with a qualifying word or phrase: however, moreover, furthermore, on the other hand:
I like coffee; however, she prefers tea.
Although these connectors look like and or but, they are not. Notice that while and and but are stuck between the two cores, these words can move around: I like coffee; she, however, prefers tea. I like coffee; she prefers tea, however. Unfortunately, many writers do not see (or hear) the difference and tend to punctuate them the same. 

Here’s what I often find: I like coffee, however she prefers tea. Whoops, just read the sentence aloud to test it. In fact, this is a sentence with two Cores where the second Core is preceded by the introductory word, however. Without the semicolon, this is a terrible error: a comma splice.

4. The second Core can serve as an explanation for the first Core: They have canceled the event: there is too much snow. Arguing purely from punctuation, one could use a semicolon here (they are both Cores); however, these two sentences don’t just sit side-by-side: in fact, the second explains the first, and only the use of a colon predicts that for the reader (remember “yoo hoo.”)
 
5. Semicolons can serve to separate sets of words in a sentence when the sets contain internal commas: We’re excited to be considering venues in these locations: New York, Monday, April 5; Boston, Monday, April 12; and Baltimore, Tuesday, April 20. (If the list is long or complicated, I'd strongly advise presenting the information in a table.)

6. Commas serve to separate a series of short Cores—usually: I walked the walk, I talked the talk, but I did not fool anyone. However, if one or more of the items in the series contains an insert, it is necessary to separate the items with semicolons: I walked the walk; I talked the talk; but, in fact, I did not fool anyone. (Remember, don’t use commas at two levels in the same sentence.) And, finally, note that when you do use a semicolon after the first Core, you must also do so before the and or but.

I think these guidelines have addressed the key ways to use a semicolon. And I hope they make sense, because their function is really to help you help your reader.