Should e.g. and i.e. have periods, e.g. "e.g.", or no periods, eg "eg"? Should they be italicized, e.g. "i.e." or not, eg "i.e"?
In formal contexts, I would go with "e.g." and "i.e.", with two periods and without a whitespace. The spellings without periods are quite popular, but informal. For example, Merriam-Webster does not have an entry for either "eg" or "ie". Wiktionary marks "eg." and "eg" as informal, and offers the following usage notes:
- Opinion is mixed about whether this term should be italicized as although it is Latin, it has become part of standard English, and whether it should be written with a separating space "e. g." as it was originally two separate words.
It also offers the following usage notes for "i.e.":
- Opinion is mixed about whether the abbreviation should be italicized, or whether there should be a separating non-breaking space as in i. e..
- ie is often found in current usage, and is perhaps now considered acceptable.
Personally, I would argue that there's no need whatsoever to italicize "e.g." or "i.e.". Both expressions are extremely common in English, and have been for a long time. They are full-fledged citizens of the English language, and as such, they do not have to be italicized as if they were foreign words.