They may be small, but their power to befuddle writers and speakers of the English language is mighty: what’s the difference between i.e. and e.g.? And what are the correct uses of these commonly confused abbreviations?
The term i.e. is a shortening of the Latin expression id est, which translates to “that is.” It is used to introduce a rephrasing or elaboration on something that has already been stated: “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.” In this example, i.e. introduces an elaboration on citrus fruits.
The term e.g. is an abbreviation of the Latin expression exempli gratia, meaning “for the sake of example” or more colloquially, “for example.” It follows that this term is used to introduce examples of something that has already been stated: “I like citrus fruits, e.g., oranges, lemons, and limes.”
One easy way to remember the difference between these two is by employing a simple mnemonic device: think of the i at the beginning of i.e. as standing for the first word in the phrase “in other words,” indicating that the clause that follows will rephrase or explain what precedes the term. E.g. is a little more straightforward since e stands for exempli meaning “example.” To ensure your mastery over these terms is not tarnished by misplaced punctuation, remember that in formal writing, e.g. and i.e. are often set off in parentheses and followed by a comma; in less formal writing, it is standard to place a comma before and after these terms.
* http://blog.dictionary.com/whats-the-difference-between-ie-and-eg/
