What’s the difference, you ask? The distinction may be slight, but it’s also significant: these abbreviations are absolutely not interchangeable. Blindly using one in place of the other creates a nasty blemish on an otherwise stellar piece of writing.
To put it simply, i.e. (from the Latin id est) translates roughly to “that is.” It is used to provide further clarification for or define a point made earlier in the sentence. For instance:
“Although she prefers to wait for the DVD release, Susie will go to the movie theater to see certain films, i.e, potential Oscar nominees.”
This sentence implies that the only movies Susie will see in theaters are potential Oscar nominees. On the other hand, e.g. (from the Latin exempli gratia) translates to “for example” and provides examples for a point made earlier in the sentence.
“Although she prefers to wait for the DVD release, Susie will go to the movie to see certain films, e.g., potential Oscar nominees.”
This sentence lists potential Oscar nominees as one example among others of the type of film Susie will see in theaters.
Having some trouble remembering the rule? Here’s an easy trick:
e.g. = for example
i.e. = in other words
If you’re looking for further clarification, check out an official grammar guide. If you’re looking for a comic spin on the subject, check out this visual lesson from the ever-hilarious The Oatmeal.