If you are like many people, you understand i.e. and e.g. based on how you’ve seen them used in other sources or contexts. But has anyone actually defined these terms for you? And did you know that they are not interchangeable? In fact, they’re as different as apples and oranges!
Although they mean different things, both terms are abbreviations of common Latin phrases. They are often found in academic writing and are used to introduce material that’s enclosed in parentheses. Here’s a breakdown of the difference between i.e. and e.g. and some tips for using each one correctly in your own writing.
I.e. is an abbreviation of the Latin term id est, which literally translates to “that is.” A good way to determine where this term is appropriate is to remember that i.e. can stand in for “in other words” (this is especially helpful because both i.e. and “in other words” begin with the letter i). I.e. is used to provide further detail when explaining a concept or term:
Unfortunately, unicorns are mythical creatures (i.e., they are imaginary and never actually existed).
In this example, the use of i.e. prefaces an explanation of what “mythical creatures” means in more detail. Try rereading the sentence and replacing i.e. with “in other words” in your head (just remember: i = in other words).
E.g. is an abbreviation of the Latin term exempli gratia, which translates to “for example.” A good memory trick for this one is to remember that e = example. This abbreviation is more common than i.e. and is used to list examples:
Dragons are a popular type of mythical creature in fantasy fiction (e.g., The Lord of the Rings, Game of Thrones, and Eragon).
In this example, e.g. introduces a list of examples of popular fantasy fiction that contains dragons.
Punctuation when using i.e. and e.g.
In addition to misunderstanding the difference between i.e. and e.g. in terms of context, many writers do not know that there are certain punctuation rules that go along with these abbreviations based on the style of English being used.
In American English, these phrases are placed in parentheses with a comma following the final period in the abbreviation:
I love all kinds of sandwiches (e.g., turkey sandwiches, bologna sandwiches, and salami sandwiches).
British English is a little different and usually offsets these phrases by placing them between commas, although a comma is not required to follow the final period in the abbreviation:
In our study we surveyed 248 students, i.e. 62% of the school’s population.
If you’re worried about how to use these abbreviations correctly in formal writing, be sure to consult the style guide you’re using. However, by following these simple rules, you should have no problem navigating the difference between i.e. and e.g.