As far as I know, "in addition" is a prepositional phrase, and you're not supposed to put a comma after a prepositional phrase with less than five words when it's at the start of a sentence. Is "in addition" an exception, or if I'm going by that rule, should I omit the comma after "in addition" as well?

The Purdue OWL says, among other things:

Common introductory phrases that should be followed by a comma include participial and infinitive phrases, absolute phrases, nonessential appositive phrases, and long prepositional phrases (over four words).

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    I can't find any other reference to this five word rule you mention. My feeling is that it should have a comma. See more here. – Josh Friedlander Apr 20 '17 at 20:56
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    Here is one: owl.english.purdue.edu/owl/resource/607/02. It states "b. Common introductory phrases that should be followed by a comma include ... long prepositional phrases (over four words)." – Natalie Apr 20 '17 at 22:25
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    'In Paris we stayed at the Ritz' sounds fine; 'In addition his mother had just died' less natural without the pause. The sentence-connector usage usually attracts a comma. Compare 'On the contrary,', 'On the other hand,'. – Edwin Ashworth Apr 20 '17 at 23:11

Good question. "In addition", in addition to being a prepositional phrase (apologise for tautology), is an adjunct. Adjuncts, according to nearly all style manuals, should be set off with a (pair of) comma(s). Josh Friedlander has done poor research: The Chicago Manual of Style clearly says, "when clauses are very short and closely connected, the comma may be omitted", which, I suspect, is what you are referring to. I, personally, don't agree with it - as it makes rules much vaguer and less precise - but it is up to you decide whether to follow it or not; regardless of your opinion on it, though, a comma should always be placed after adjunct introductory phrases such as "in addition".

  • "should always"? what will happen if someone doesn't? blow up? get no gift from Santa? These are style guides. There's no punctuation overlord of English. – AmE speaker Nov 8 '17 at 23:30
  • @Clare Pedantry at its best. Of course, you don't absolutely HAVE TO put commas anywhere, but if you ever decide to use them, putting a comma after (introductory) adverbial phrases is one of the first things you should do. Nearly all style manuals agree on this. The reasons are obvious - if adverbial phrases are not marked with commas, the sentence may become ambiguous and may be interpreted in more than one way, giving rise to confusion. For example, the sentence, "Basically explained material in school really is only one of many reasons for the popularity of pseudoscientific theories – Max Nov 9 '17 at 20:42
  • such as creationism" can be interpreted in FOUR different ways: explained material truly is one of the reasons for pseudoscience; material explained only basically truly is one of the reasons for pseudoscience; it may seem like explained material is one of the key reasons for pseudoscience, but, really, it is just one of many; it may seem like material explained only basically is one of the key reasons for pseudoscience, but, really, it is just one of many. If we don't punctuate adverbial phrases then there is no reason to punctuate anything. I think you should reconsider you downvote - if – Max Nov 9 '17 at 20:50
  • that indeed is your primary reason for it. – Max Nov 9 '17 at 20:51

I always use a comma after "In addition."

I try to use a comma (or some other punctuation) when there is a significant pause, because that's what commas are for — to indicate a pause.

Other punctuation that can be used to indicate a pause are em dashes, colons, and semicolons. However, in the case of "in addition," you would only use a comma.

  • 4
    But . . .. "In addition to being a jerk, he is also a boor." (No comma needed after "In addition.") – rhetorician Apr 21 '17 at 1:21
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    That would be a fragment. – Natalie Apr 21 '17 at 2:28
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    "that's what commas are for — to indicate a pause." That is a misconception that is all too common. Commas exist to denote grammatical information. They are sometimes denoted in spoken speech with a pause, but using merely to indicate a pause is an abuse of punctuation, impedes communication, and can change the meaning of a sentence. Commas are not for whenever you feel like putting one in. And throwing a colon or semicolon into your sentence just to "indicate a pause" is even worse. – Acccumulation Nov 9 '17 at 5:03
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    Debbiesym, we generally try to back up our answers with evidence instead of going from personal preference. Do you have any supporting website or source for your claim? – KumaAra Nov 9 '17 at 7:18
  • @Acccumulation It’s true commas denote grammatical information. But they also indicate a pause in speech. When readers see a comma — one that’s properly placed — they almost always pause. Try reading a long passage without pausing at the commas. It’s difficult to do. (I recommend the “To be or not to be” soliloquy from Hamlet.) There are other ways to indicate a pause, of course, and there may be places without a comma where the reader wants to pause. But I think it’s hard to make the case that commas don’t have anything to do with pauses. – debbiesym Nov 13 '17 at 20:14

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