Many people use these interchangeably, but as you look into what “i.e.” and “e.g.” actually mean, you start to see how they are distinct. Specifically, “i.e.” is an abbreviation for the Latin “id est”, more or less meaning “that is”. “E.g.”, on the other hand, is an abbreviation for the Latin “exempli gratia”, meaning “for the sake of example”, or the easier to remember shortened version, “for example”.
As a general rule, if you can substitute in “for example” where you’ve used “e.g.”, you are probably using it correctly. Likewise, if you can substitute in “that is” where you’re using “i.e.”, you are also probably using it correctly.
One way to remember what “i.e.” and “e.g.” actually mean is to notice that “i.e.” starts with an “i”, as does the second word in “that is”. Further, “e.g.” starts with an “e”, as does the second word in “for example”.
The key distinction here with “i.e.” versus “e.g.” is that with “e.g.” you are simply stating one or more examples, of which there could be many more items that you didn’t include. With “i.e.”, you aren’t talking about anything but what you specifically say.
So to illustrate the difference between “i.e.” and “e.g.”, let’s look at a specific example:
I love sports, e.g., baseball, basketball, and tennis.
I love sports, i.e., baseball, basketball, and tennis.
In the first sentence, the use of “e.g.” (for example) implies that there are other sports besides baseball, basketball, and tennis that I love. In the second sentence, the fact that I used “i.e.” (that is) indicates that the only sports I love are baseball, basketball, and tennis.
If you’re still having trouble remembering the distinction with “that is”, another tip from Grammar Girl is to throw out the Latin definition altogether and just think of “i.e.” as, “in other words”. So, “I love sports, in other words, baseball, basketball, and tennis.” So to sum up, “e.g” = “E” = “Example” | “i.e.” = “I” = “In other words”.
Another potential bugaboo when it comes to the use of “i.e.” and “e.g.” is whether or not to put a comma after them when using them in a sentence. What to do here is somewhat personal preference, as well as what side of the pond you are on. Most American English writing style guides do recommend including the comma (e.g., Chicago Manual of Style and the Blue Book of Grammar and Punctuation).
You can see why this would be the case when you go back to the meaning of “i.e.” (that is) and “e.g.” (for example). For example, you wouldn’t exclude the comma after the preceding “example” in this sentence. That being said, you might think it looks messy to have a comma following a period, so some American English writers elect not to include it.
On the other hand, most British English stylistic guides, such as OED, state that you should not put a comma after “e.g.” or “i.e.” Further, they also recommend that you never capitalize the “e” or the “i”, even when starting a sentence with “i.e.” or “e.g.” This is contrary to many American English guides which recommend capitalizing the “e” or “i” if you’re starting a sentence with one of those abbreviations.
The bottom line is that if you’re writing for professional publication in the United States, it’s probably best to go with the comma after “i.e.” and “e.g.” If you’re writing for professional publication in areas where British English is king, you should probably exclude the comma. If you’re simply writing a blog posts, it’s your blog, do what you want, just be prepared for a Grammar Nazi or two to call you out on it from time to time either way, depending on where they are from.
Another common stylistic mistake used (one I myself have been guilty of on numerous occasions) is to include an “etc.” after an “e.g.” list. Because “e.g.” has been used, “et cetera” (which is Latin for “and other things” or “and so forth”) is implied, so it shouldn’t be included at the end of such a list.
If all these grammatical and stylistic rules surrounding “i.e.” and “e.g.” seem cumbersome, you can, of course, simply not ever use them. They are a substitution for things like “that is” and “for example”, so you can always just use those words or other similar phrases instead where the grammatical rules are often more self evident.
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