This is an abbreviated version of what is in my book on these eight parentheticals.
PARENTHETICAL TO INTRODUCE AN APPOSITIVE
Sometimes, when a person wants to explain, reiterate, rename, or restate something — that is, he wants to use an appositive — he uses a parenthetical before the appositive.
These are the expressions most commonly used as parentheticals before an appositive:
…that is namely
…i.e. to wit
…for example in other words
…e.g. for instance
The punctuation for these words falls into six categories:
1. When the parenthetical is followed by a fragment at the end of the sentence, use commas around the parenthetical.
…I am sure it was a large car, that is, a sedan.
…He was in desperate need of a specialist, namely, a surgeon.
…She showed me the selections, e.g., the carpet samples.
2. When the parenthetical is followed by a complete sentence at the end of the first sentence, put a semicolon in front of the parenthetical and a comma after it.
…I am sure it was a large car; that is, it was a sedan.
…He was in desperate need of a specialist; namely, he needed a surgeon.
…She showed me the selections; e.g., I saw carpet samples.
NOTE: If one or both of the sentences are particularly long, it is probably better to use a period before the parenthetical rather than the semicolon.
…She was traveling a little faster than I would have liked her to. That is, she was really speeding in an area that was more of a residential neighborhood.
3. When the parenthetical is followed by a list at the end of a sentence, put a colon in front of the parenthetical and a comma after it.
…We toured four cities: that is, Reno, Las Vegas, Phoenix, and Tucson.
…I sent it to them immediately: i.e., Jim, Bill, and Tony.
…The tax errors were in several categories: e.g., supplies, travel, gifts.
4. When the parenthetical and the appositive are at the end of the sentence and the sentence is over and the appositive renames something at the beginning of the sentence, put a dash in front of the parenthetical and a comma after it.
…I had a major headache when she called me into her office and was really having trouble concentrating — that is, a migraine.
…He has been accused of a crime that is all too common in our society today — namely, grand theft auto.
…That is exactly what we had discussed and settled on — that is, that he would pay off the loan in full by March 1.
5. When the parenthetical is in the middle of the sentence, put a dash before the parenthetical and a comma after it and put a dash after the appositive.
…I saw him early in the day — that is, around 7:30 — and did not see him again.
…There were three — e.g., red, pink, and salmon — that she particularly liked.
…I had several — i.e., John, Joe, or Harry — that I was going to recommend.
6. When a question is followed by a parenthetical, which is then followed by a second question or clarifying information, put a question mark after the question. Put a comma after the parenthetical and a period or a question mark at the end of the second element, depending on the intonation you hear as it is said.
…What time did this occur? That is, what time did he call?
…Do you know the name he was using? In other words, his alias(?) OR (.)
…Did he show you the line? For example, some of the power tools(?) OR (.)
…What time did this occur? What time did he call, that is?
…Do you know the name he was using? His alias, in other words(?) OR (.)
…Did he show you the line? Some of the power tools, for example(?) OR (.)