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Suppose I have a phrase that expresses two statements as being equivalent. The details aren't important (they happen to be mathematical statements, and for the purpose of illustration, let's use "A is greater than B" and "C is greater than D"), but the structure of the phrase is:

A>B or equivalently C>D

What's the correct punctuation here - comma or semicolon, where does it go, and why? Possibilities (which all seem somewhat reasonable...my intuition is failing me here):

A>B or, equivalently, C>D

A>B or equivalently, C>D

A>B, or equivalently C>D

A>B or equivalently; C>D

A>B; or equivalently C>D

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I know you've probably got what you came for, but it'd be great if you'd login again and mark an answer as correct :) –  andrewdotnich Apr 10 '12 at 3:12
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3 Answers

I would use parentheses to show the "aside" nature of the second half:

"A > B (or equivalently, C > D)"

EDIT: OP mentioned the phrase is already in parens, and is reluctant to nest. I still think it's acceptable, because it's only a few words. Perhaps use different symbols, like []?

If the phrase is at the end of a sentence, you could also use just a semicolon:

"(… A>B; equivalently, C > D. …)"

In this case, the or is unnecessary because the semicolon already signals a break in the main thought.

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problem is, I'm already using this phrase in a parenthetical statement. Too bad I can't nest parentheses in English. OT: you must be a lindy hopper... –  jd444 Apr 4 '12 at 1:10
"I can't nest parentheses in English" — why not? :) –  andrewdotnich Apr 4 '12 at 1:22
And yes, I'm a lindy hopper - you? –  andrewdotnich Apr 4 '12 at 1:23
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I like the parentheses idea, but, since we're already in the middle of a parenthetical statement, how about a dash?

A >B – or, equivalently, C >D

If the sentence doesn't end with C >D, then use a second dash to continue:

(The parenthetical statement starts here with A >B – or, equivalently, C >D – and then the rest of the statement comes after the second dash).

According to one website:

Use a dash [ — ] as a super-comma to set off parenthetical elements, especially when those elements contain internal forms of punctuation...

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Not sure why you were downvoted, like this idea too… –  andrewdotnich Apr 4 '12 at 6:48
Somebody downvoted this idea? Oh, dash it all! –  J.R. Apr 4 '12 at 8:23
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A>B, or equivalently C>D" or "A>B or, equivalently, C>D".

For the first one, it would be: a>b or c>d. After stating a relationship with "or", you then include how the two are related by including it between two commas.

The second one would mean that either a>b or that equivalently. This makes no sense.

It cannot be the last two because collins separate complete thoughts.

One way you could figure this out yourself is by reading it out loud with extended pauses for each comma, and see which one makes sense.

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I'm not a fan of the "reading it aloud" heuristic. For example, it's common to pause in speech before an and which joins a non-independent clause, but there shouldn't be a comma there. I'm not so sure about the semicolon being incorrect. Technically "X>Y" is an independent clause - subject: "X" predicate: "is greater than Y". Not positive though... –  jd444 Apr 3 '12 at 22:31
The reading out loud is just a suggestion and could be one of the steps you take. In "A>B or equivalently; C>D", "A>B or equivalently;" is not a complete statement. Equivalently what? Nor is "or equivalently C>D". –  stas Apr 3 '12 at 22:36
you're probably right that semicolon is the wrong punctuation here. Commas it is. –  jd444 Apr 4 '12 at 1:11
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