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Some of the most consistent problems that I see while editing academic papers are the incorrect usage and inconsistent punctuation of i.e. and e.g. These two elucidating pairs of letters seem to cause quite a few problems for even the most erudite of academic writers, so the subject of how to use the abbreviations i.e. and e.g. properly and consistently certainly deserves its own post. In many cases, it’s clear to me as an editor that the author just doesn’t know which one to use, even though the rest of their project may be brilliant. In other cases, it’s clear that the author knows which one to use, but the inconsistent punctuation used throughout the project reveals that effective comma usage remains a mystery. This post should clear up both of those issues.
To understand the rules on both proper usage and the proper punctuation when using i.e. or e.g., it’s helpful to understand their origins. It’s true that too many English grammar and punctuation rules aren’t rules at all. English is full of ambiguity and exceptions. So isn’t it a good thing i.e. and e.g. originate in Latin? Both letters are abbreviations for Latin phrases and are meant to clarify something or provide additional information. The letters i.e. come from the Latin phrase id est, which means that is. The letters e.g. come from the Latin phrase exempli gratia, which means for the sake of example.
Understanding their origins, then, clarifies the scenarios in which we should use each phrase. The letters i.e. are only used when restating or more succinctly clarifying something that was already stated, that is, it is not used to precede a list of examples. A list of examples is primarily the function of e.g., as demonstrated by its Latin origin, exempli gratia.
To illustrate: I love the best team in baseball, i.e., the Milwaukee Brewers. In the preceding sentence, I use i.e., because I’m clarifying that the best team in baseball is the Milwaukee Brewers and none other. There is no other best team in baseball.
Argue with me on that. Go ahead. I dare you.
In contrast, I love all the best sports teams, e.g., the Milwaukee Brewers, the Green Bay Packers, and the Milwaukee Bucks. Here, I’m providing a list of examples, and it is not necessarily an all-inclusive list. I could love other great sports teams, e.g., any sports team fielded by the University of Wisconsin. See what I did there?
Likewise, remembering the origins of the abbreviations i.e. and e.g. aids in remembering that a comma should be placed after the letters. Simply replacing the Latin abbreviations with their English translations demonstrates the point. Using the above examples, we could just as easily write the following: I love the best team in baseball, that is, the Milwaukee Brewers; and I love all the best sports teams, for example, the Milwaukee Brewers, the Green Bay Packers, and the Milwaukee Bucks. When using each phrase in English, a comma would be appropriate; therefore, a comma is appropriate when using the Latin abbreviations. Although a comma is almost always called for in American English, British English may sometimes omit the comma. If you don’t want to take my word for it, check out the Grammar Girl post on the subject. She has worked up a chart demonstrating which style guides recommend a comma and which ones don’t.
Here’s a hint to save you some time: Nearly all style guides recommend using a comma after i.e. and e.g. when introducing clarification or examples, respectively.
If all that is too complicated to remember, try using a memory trick. The trick that I have found to be the most popular and effective involves coming up with your own English translation for the letters. When using i.e., pretend that it means in essence. This will help remind you that you’re clarifying or restating what you’ve already said. For e.g., pretend that it means example given. This will help remind you that you’re providing a non-exhaustive list of examples.