Which of the following ways of using i.e. in a sentence is correct?

1) The elephant is a pachyderm, i.e., an animal with thick skin and nails resembling hooves.
2) The elephant is a pachyderm (i.e., an animal with thick skin and nails resembling hooves).

Also, if we use i.e. as in the first sentence, should we use a comma before it?

  • A modern way to use "i.e." is to use it without periods and italicize it, i.e., ie. One way to clean things up is to get rid of unncessary periods. And I think that because fewer people realize that "i.e." comes from an abbreviation in Latin that ie is now used (by those in the know) as a sort of term, or even a symbol, for "that is" that doesn't necessarily hearken back to the Latin words. The same for eg (for example). Of course, one still has to know what the English words are, or at least to use one and when the other--which is another thing many writers fumble at. – user6951 Feb 27 '15 at 5:34

First question: The i.e., which means "that is", is unnecessary in both sentences. It's clear from context that "an animal with thick skin and nails resembling hooves" is a definition of "pachyderm". However, it isn't necessarily incorrect, just verbose.

Second question: Yes, the comma is necessary, but style manuals don't all agree on whether the second comma is required. Some publishers don't require it, some do, and some forbid it.

Third question: "When should I use i.e.? Answer: When it isn't clear that what follows is in apposition. Two good examples of when i.e. is useful:

"He did not respond, i.e., he declined".
"Eating squirrel taco without any ranch dressing is like playing leapfrog with a unicorn, i.e., a very bad idea."

In both sentences immediately above, it's not as clear as in your two sentences that the final phrase is apposite to the initial clause, especially in the second example: What exactly does "a bad idea" refer to?

Rule of thumb: Avoid these Latin abbreviations whenever possible if they seem superfluous. Always avoid unnecessary words.

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  • Thanks a lot for explaining how and when we should use i.e :) . When do we use i.e within parenthesis ? – kartshan Apr 26 '13 at 6:46
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    Using parentheses is a style choice. Unless your prescribed style manual tells you when to & not to use parenthetical remarks, it's up to you. A good rule of thumb is to avoid using them too often: they clutter up a page. You can see this very (very (very (very))) clearly on any page in a paper that uses the inane APA Style Guide, which requires all reference citations to be enclosed in parentheses. – user264 Apr 26 '13 at 7:04

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