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William Strunk's Rules of Usage states:

If a dependent clause, or an introductory phrase requiring to be set off by a comma, precedes the second independent clause, no comma is needed after the conjunction.

Strunk's example illustrates the point:

The situation is perilous, but if we are prepared to act promptly, there is still one chance of escape.

However, I would be tempted to put a comma after the "but," like this:

The situation is perilous, but, if we are prepared to act promptly, there is still one chance of escape.

So, I know you're thinking, "Well, Strunk's Rules of Usage says that you're wrong. No comma."

But is Rules of Usage really the best source? I'd like to see this rule in a more contemporary and authoritative source, like the Chicago Manual of Style.

There are many instances — such as in The New York Times — where the comma is included before a parenthetical comment that comes after a coordinating conjunction.

Any authoritative source on the issue?

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Nitpick: it is William STRUNK, not STUNK. – Chris B. Behrens Feb 3 '11 at 20:32
Oops, good catch. Thanks! – Paul Murray Feb 3 '11 at 22:07
up vote 6 down vote accepted

Ordinarily parenthesis should be marked with commas on both sides. But Fowler recommends that the first comma should be left out after a coordinating conjunction if what follows is a simple adverbial phrase—if I interpret him correctly. (Coordinating conjunctions are and, or, but, and possibly some semi-conjunctive adverbs like so, therefore, however, etc.) The comma should be retained before a subordinate clause or when its omission would cause ambiguity. This probably includes conjunctions that are not at the beginning of a sentence. Fowler's advice seems balanced and practical.

  • Cleopatra appeared poised and composed. But on the inside, she was seething with rage. — Simple adverbial phrase at the beginning of a sentence.

  • Her only option was to support Mark Anthony once again. But, if he should perish, it would be the end of her. — Not a simple adverbial phrase but a clause.

  • She knew her cause was lost and, in a fit of final despair, had a serpent brought in to extinguish her life with its venom. — Not at the beginning of a sentence.

The relevant text from Fowler's The King's English follows. He is arguing for general laxity with adverbial phrases, and would generally allow both commas and no commas around them. He goes on to say that, if commas are used, one must never omit one but write the other; however, he gives the above rule as an exception, in order to avoid an abundance of commas, logical though they might be.

Laxity once introduced, however, has to be carefully kept within bounds. It may be first laid down absolutely that when an adverbial clause is to be stopped, but incompletely stopped, the omitted stop must always be the one at the beginning, and never the one at the end. Transgression of this is quite intolerable; we shall give several instances at the end of the section to impress the fact. But it is also true that even the omission of the beginning comma looks more and more slovenly the further we get from the type of our above cited sentence. The quotations immediately following are arranged from the less to the more slovenly.

  • His health gave way, and at the age of fifty-six, he died prematurely in harness at Quetta.—Times.

  • If mankind was in the condition of believing nothing, and without a bias in any particular direction, was merely on the look-out for some legitimate creed, it would not, I conceive, be possible...—Balfour.

  • The party then, consisted of a man and his wife, of his mother-in-law and his sister.—F. M. Crawford.

  • These men in their honorary capacity, already have sufficient work to perform.—Guernsey Evening Press.

It will be observed that in the sentence from Mr. Balfour the chief objection to omitting the comma between and and without is that we are taken off on a false scent, it being natural at first to suppose that we are to supply was again; this can only happen when we are in the middle of a sentence, and not at the beginning as in the pattern Cranmer sentence.

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I don't have a membership to the CMS, so I can't speak to their take on it. But I would say that the meaning, or at least the tone that you're trying to communicate it subtly different between the two phrases. In your punctuation, the speaker is expressing doubt that "we are prepared to act promptly", and perhaps expressing the subjunctive as a bit of an aside.

And if the actual meaning is different, then rules of usage be damned. I personally would punctuate it thusly:

The situation is perilous; but - if we are prepared to act promptly - there is still one chance of escape.

No commas at all.

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Well, that's not my sentence, just the example from Rules of Usage. I was looking more for a generic guideline — someone was trying to tell me that a comma after the conjunction is just plain wrong. In any case — and for what it's worth — I do like your version of the sentence. – Paul Murray Feb 3 '11 at 22:04

I was once an editor of a law review journal. I did not find Strunk helpful as to this issue. Generally, I would insert a comma after the conjunction but, for the sake of clarity, I would not place a comma before the conjunction. My wife, an English major and also a lawyer, however, disagrees with me. Of all of the grammar issues we have ever discussed, this is the only issue upon which we disagree.

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I don't have a lot of time for style guides anyway, and as I understand it, Strunk is better-known as a target of criticism than as a serious contender for the misguided concept of "absolute authority". But on the principle that "less is more", and also in line with the modern trend towards using less commas overall, they're quite correct to say that first comma is unnecessary. And like you, I would discard it. It adds nothing to legibility, and the sheer preponderance of commas is just pointlessly distracting. AND you wouldn't pause in speech! – FumbleFingers Sep 9 '12 at 21:43

"Well, Stunk's Rules of Usage says that you're wrong. No comma."

"no comma is needed" does not mean "it is wrong to use a comma."

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Hmm, good point. This arose from a debate where the other side was arguing that it was just plain wrong. The CMS has a really great Q&A Page, and I really like the way they answer a lot of questions, like this one. People come in with a lot of nit-picky questions, and they always seem to respond along the lines of "do whatever makes the most sense." I like that approach. – Paul Murray Feb 3 '11 at 21:59
I do too. Writing is about communication. The point is to be as clear as possible. – horatio Feb 3 '11 at 22:06

Well my wife just showed me the new Chicago Manuel of Style. According to provisions 6.28 and 6.32, I lose the argument. As always, she wins. Do not insert a comma after a conjunction, but according to the Chicago Manuel of Style, you should insert a comma before the conjunction.

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I don't know if you can't post comments because you don't have sufficient reputation points, but the moderators won't like you posting comments as answers. I'm actually going to vote to close this question now it's come to my attention (pointless and subjective, imho). But please stick around, and post some answers that can get upvoted, so you'll be able to post real comments! – FumbleFingers Sep 9 '12 at 21:49

protected by RegDwigнt Sep 9 '12 at 21:20

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