Students of mine asked:
1.1. What is the difference between i.e. and e.g.?
I.e. is the abbreviation for the Latin phrase id est, which means “that is (to say).”
E.g. stands for the Latin phrase exempli gratia, which means “for (the sake of) example.”
Here are two examples taken from Dictionary.com:
1. “I like citrus fruits, e.g., oranges and lemons” (for example, oranges and lemons).
2. “I like citrus fruits, i.e. the juicy, edible fruits with leathery, aromatic rinds of any of numerous tropical, usually thorny shrubs or trees of the genus Citrus” (that is to say, the juicy, edible fruits…).
In the first sentence (1) you are giving an instance, whereas in the second (2) you are giving an explanation.
1.2. When should we use these abbreviation?
These abbreviations are mostly used in formalized contexts (such as grammar books, treatises and the like), in writing rather than colloquially. However, i.e. is known to have been frequently used in colloquial American English over the last three decades – which makes it more “popular” than e.g. in spoken English on that continent.
My suggestion is to think of them as Math language: you are more likely to refer to the “pluses of,” the “minuses of,” or the “equation within,” say, relationships, than to use q.e.d. (from the Latin phrase “quod erat dēmōnstrandum,” meaning which was to be demonstrated) during a casual conversation. As David Crystal was commenting on one of his posts, “Obviously, if people aren’t taught Latin, they’re not going to understand jokes based on Latin. And the way things are going in modern foreign language teaching, I wonder how many of these jokes will make sense to young people today.”
My final recommendation? Every speaker has the freedom of choosing the words they use, from the most mundane to the very specialised. Beware, though, of overzealous uses of abbreviations like i.e. and e.g., unless, of course, you are in the process of reading out loud from a textbook. You can always use “for example” or “in other words” instead of e.g. and i.e. during a conversation. If, on the other hand, your intention is to revolutionise the common language of conversation, to make waves, or, in the very least, to stand out in an English speaking crowd, be bold and dare to use the unexpected! Surprises are bound to occur every step of each way – the safe, the less safe, or any other variety!
More questions? Go ahead, and ask!