While my academic choices may have strayed from the most practical paths, they have not been completely useless*. For example, I know that "e.g." is the abbreviation of the Latin expression, exempli gratia, which translates as "for example."
I also know that it should be punctuated with a period after each letter. When used in a sentence, it should be followed by a comma and then an open-ended list (i.e., not a finite list) of examples, thus:
I like many kinds of cheeses, e.g., Gruyère, ricotta, and cheddar.Note that this list is not complete. It only mentions a few examples.
I also know that "i.e." is the abbreviation of id est and simply means, "that is." It is used to reiterate something in different words. (In "tight" writing, it is often redundant, but can still be warranted if you are explaining a confusing topic; in most cases, you are better off to simply use the wording that follows the "i.e.".)
As with e.g., it also should be followed by a comma.
Kanga, from Winnie-the-Pooh, is a marsupial (i.e., carries her child, Roo, in a pouch).See what I mean? That sentence could have been much more clearly written this way:
Kanga, from Winnie-the-Pooh, carries her child, Roo, in a pouch.Now, here's where people get confused and sometimes use one abbreviation when they mean the other. "I.e." may be used to preface a list, but (and it's a big but), it must be a complete list of all the possible items. For example, if I modify the cheese example for e.g.:
I like only three kinds of cheese, i.e., Gruyère, ricotta, and cheddar.In summary, you have two things to remember.
- e.g. = for example, and i.e. = that is.
- Follow each with a comma.
Is that clear as mud?
(By the way, my favourite part of writing these posts is coming up with the examples.)
* Except the Old Norse. That has proven to be singularly useless. Even if I ever go to Iceland, which I would love to do, the language I learned is dead. Deader than a doornail.