Comma after ‘i.e.’ and ‘e.g.’

by Jakub Marian

Tip: See my list of the Most Common Mistakes in English. It will teach you how to avoid mis­takes with com­mas, pre­pos­i­tions, ir­reg­u­lar verbs, and much more.

The abbreviations i.e. (which means “that is” or “in other words”, from Latin id est) and e.g. (which means “for example”, from Latin exempli gratia) are always preceded by a punctuation mark, usually a comma or a bracket, as in

They sell computer components, e.g.[,] motherboards, graphic cards, CPUs.
The CPU (i.e.[,] the processor) of your computer is overheating.

The question is, should a comma also follow the abbreviation? The answer is: It depends on whether you want to follow the American style or the British style.

In British English, “i.e.” and “e.g.” are not followed by a comma, so the first example above would be:

They sell computer components, e.g. motherboards, graphic cards, CPUs.

Virtually all American style guides recommend to follow both “i.e.” and “e.g.” with a comma (just like if “that is” and “for example” were used instead), so the very same sentence in American English would become:

They sell computer components, e.g., motherboards, graphic cards, CPUs.

Nevertheless, many American authors and bloggers are unaware of this recommendation, so you are much more likely to read a text with no commas after “i.e.” and “e.g.” written by an American than a text written by a British author with the commas included.

By the way, if you haven’t read my guide on how to avoid the most common mistakes in English, make sure to check it out; it deals with similar topics.