Even though Latin is considered a dead language (no country officially speaks it), its influence on other languages is significant. Latin words and expressions are present in virtually all languages around the world, as well as in different scientific and academic fields. While writers of dissertations and other formal papers are cautioned to avoid foreign words or phrases unless there really is no natural English equivalent, a number of Latin words and phrases are standard in academic writing.
Two of the most commonly used Latin expressions are also two of the most commonly confused.
Exempli gratia, abbreviated e.g., means for example; and id est, abbreviated i.e., literally translates as that is, and typically means in other words. The two phrases are often incorrectly interchanged. The decision whether to use i.e. or e.g. should be based on whether “for example” or “that is” is what you want in the sentence.
Use e.g. when giving examples of the topic you are discussing but don’t intend to list everything possible to illustrate it. Think of what precedes e.g. as the name of a category and what follows as a few things—but not everything—that would fit into that category:
Many real numbers cannot be expressed as a ratio of integers (e.g., the square root of two).
The square root of two is just one example of the many real numbers that can’t be expressed as a ratio of integers.
Use i.e. to clarify what has already been stated or to explain or define what you just said in a different way:
The elephant is a pachyderm (i.e., an animal with thick skin and nails resembling hooves).
To help you remember the distinction between e.g. and i.e., imagine that e.g. stands for example given and i.e. means in essence. Some people associate the sound of the word example with the letters e.g. – when you use e.g., you’re offering an “egg sample.”
If you're still confused about when to use each abbreviation, you can always just write out the words for example or in other words. There's no rule that says you have to use i.e. or e.g.
Dos and Don'ts
There is no need to italicize i.e. and e.g. when you use them in your writing. Even though they are abbreviations for Latin words, they have entered the common lexicon and are considered a standard part of the English language. (They are italicized in this article because the writer is talking about them—in actual usage, no italics are required.)
Because they are abbreviations, a period is required after each letter, but there is no space between letters.
American English usage requires a comma following both i.e. and e.g., as shown in the earlier examples.
Various authorities (e.g., the Chicago Manual of Style and the APA Publication Manual) support the rule that the abbreviations e.g. and i.e. should be used only in parenthetical comments injected into your text (as the example in this sentence illustrates). If you choose not to use parentheses, spell out the English equivalent instead. For e.g. use for example; for i.e. use that is or in other words.
Another confusing Latin term
Your CV is a vital tool in your professional development toolbox, but be sure you use the right words to talk about it. The correct singular form is curriculum vitae, translated literally from Latin as “course of life.” (For grammarphiles, vitae is the genitive form of life, not the plural.) The plural form is curricula vitae (courses of life: “Jane and Jake submitted their curricula vitae to the fellowship committee.”) The informal shortened form is vita (singular) – translated from the Latin for life – or vitae (plural), lives. Abbreviations are often used: CV or CVs. While it is appropriate to write either curriculum vitae or just vita, it is incorrect to use the phrase curriculum vita when referring to a CV.