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It seems that "e.g." is always followed by a comma but "i.e." is not. Why is that?

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7 Answers 7

up vote 35 down vote accepted

The distinction probably emerges from their different meanings in Latin, which grants them different usages in writing.

E.g. (exempli gratia in Latin, meaning “for example”) should be generally followed by a list of examples. Thus, adhering to proper English style usually requires commas to follow e.g. to delimit the beginning of that list.

I.e. (id est in Latin, meaning “that is”) is used to recapture the meaning of an antecedent clause by rephrasing. Typically, it is only followed by a clause describing a singular entity, and so does not require a comma.

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+1 for using e.g. without comma and i.e. with. –  Tim N Mar 13 '11 at 12:31
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@Tim I used neither term in their usual sense, I only referred to them as proper nouns. Besides, I did use a comma with the first e.g.. –  Uticensis Mar 13 '11 at 12:41
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I thought it was intentional. Please edit your answer so I can remove the upvote. :p –  Tim N Mar 13 '11 at 12:43
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Hm, you introduced an error in your second edit. You changed which means "that is" in Latin to which means "that is" is Latin... –  Timwi May 3 '12 at 12:39
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It seems irrelevant that e.g. often has a list of items following it and i.e. does not; the introduction to the list has no need of being explicitly delimited from the e.g. –  mgkrebbs Jan 25 at 6:31
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Grammar Girl did some research and determined that five out of six style guides lean toward using a comma after both i.e. and e.g. Here's the gist of the table she shared on her site:

  • Chicago Manual of Style: A comma is usually used
  • Blue Book of Grammar and Punctuation: Commas are preferable/optional
  • The Columbia Guide to Standard American English: Editors require a comma
  • The Guide to Grammar and Writing: The commas makes good sense
  • Lynch Guide to Grammar: Should be followed by comma
  • Fowler's Modern English Usage: Commas do not usually follow i.e. (No comment on e.g.)

She also gives an excellent rundown on when to use each of these abbreviations. She suggests that you think of i.e. as meaning "in other words" and e.g. as meaning "for example." I recommend reading her whole article.

Addition: My daughter just reminded me of an excellent and entertaining explanation of usage for i.e. and e.g. from The Oatmeal. This one I can't summarize. You must view it in all its glory.

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Good link, Kristina, probably better than my answer. It'd help if you'd summarize the most useful part of your link for the benefit of readers so they might not have to click through. It's easy rep points, and besides, links are susceptible to link rot, i.e. they die. –  Uticensis Mar 13 '11 at 18:40
    
thanks for the great link, +1. I agree with @Billare that if possible please summarize the key takeaways from that article. It will be helpful to readers on this site. –  evergreen Mar 13 '11 at 22:35
    
@Billare & @evergreen, Thanks for the suggestions. Will edit. : ) –  Kristina Mar 14 '11 at 20:28
    
I like how the Oatmeal cartoon specifically addresses the comma issue, stating that most style guides recommend using a comma after the abbreviation, and yet in this panel, they have one ‘i.e.’ with a following comma, and one without! –  Janus Bahs Jacquet Aug 26 '13 at 8:43
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It is not true that i.e. is never followed by a comma, nor that e.g. is always followed by a comma. You could also write sentences like the following.

Similar dynamics that resulted in the development of new local art forms have been documented elsewhere (e.g. Chibnik 2008).
My walking boots are synthetic, i.e., not leather or suede.

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+1 for deciding individually for each case. I really dislike the widely-used rule that “e.g.” (and sometimes “i.e.”) is always followed by comma. –  Konrad Rudolph Mar 13 '11 at 16:00
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I think it’s clear that e.g. has to have full stops/periods. As for using a comma after it, that should only be done in some rare cases, as in the sentence “e.g., i.e., and other abbreviations of Latin forms are often a source of confusion for English learners.” In other cases, I can see no logical reason for it to be used except a puzzling convention followed by some writers. As for convention, style guides typically don’t recommend this. Why not follow logic rather than convention, or if you follow convention, follow all major style guides, which use e.g.? I recently wrote a blog post on this issue at http://www.makeyourenglishwork.com/2012/05/17/eg-or-e-g/ if you’re interested.

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I strongly agree that one should write “for example” and “that is” — or their equivalents — out in full and in English. –  tchrist May 17 '12 at 19:03
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I think we will usually use a comma. We can confirm the same by substituting the abbreviation with original word, i.e., with "For example" and "That is" in this case. E.g.:

I like you, that is, I think I like you.

Although I am not sure what will be case if the sentence ends with e.g. or i.e.

  • I think I will die soon. I did not do anything in my life. But still it might not be a complete waste, i.e. (e.g.)...
  • I think I will die soon. I did not do anything in my life. But still it might not be a complete waste, i.e. (e.g.),..

The first one seems correct to me.

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Please change My walking boots are synthetic, i.e., not leather or suede. to My walking boots are synthetic, i.e., not leather nor suede. Nor is not used enough.

Also, it is easy to remember which to use, i.e. or e.g., by thinking of i.e. as 'in essence'. That way, you never mix them up.

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I would always place a comma after ie. and eg.

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protected by tchrist Jul 1 at 0:46

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