I.E. and E.G.
The English language has a lot of words borrowed from Latin and words with Latin roots. I.E. and E.G. are abbreviations of Latin words. There are some clear reasons why Latin features so heavily in the English language—Norman French is very close to Latin, and the Norman invasion and conquest of England in the year 1066 resulted in the English speaking A LOT of Norman French! Furthermore, Latin was the language of the church and academia (later medicine, and science) making it the go-to second language for the learned, and upper classes all over Europe.
I.E. and E.G. are 2 Abbreviations of Latin Words
So, What do I.E. and E.G. Mean?
“I.E.” is an abbreviation for the Latin phrase, id est. That translates in English to that is, as in “that is to say” or “in other words”.
“E.G.” is an abbreviation for the Latin phrase, exempli gratia. That translates in English to for example, or “for the sake of example”.
How did these phrases and their abbreviations survive into present-day usage? The same way you know and use “lol”—culture and common habit. All the hip, important people were using them (the abbreviations i.e. and e.g.) so everyone else did too…and they all just kept right on using them.
Now that you know the translated definitions for each of the abbreviations when to use which should be more evident. You’re listing examples you use e.g. For example:
The English language instructor listed the classes’ most common errors, e.g., incorrect verb tense usage, using non-words, and omitting articles in sentences.
Now I want you also to note that there is a comma, used before and after e.g., some modern style guides say one is not necessary after, however, I think with any writing rule it’s always better to err on the side of caution particularly in professional writing.
The abbreviation i.e. is used when you want to rephrase to clarify something you wrote. For example:
Knowing how to speak English is a valuable skill—i.e., you are more likely to advance your career if you work for a multi-national corporation.
Now here I want you to notice that I used an elongated dash before i.e. and a comma after. This abbreviation is more akin to an aside and is, therefore, most often used with a dash or parenthesis.
*NOTE—e.g. may also be used in parenthesis. Both abbreviations go inside the parenthesis and have a comma following the abbreviation.