I’ve seen the abbreviations “i.e.” and “e.g.” used often and interchangeably in various places (i.e. in lectures at school)to, I take it, indicate an example of something. But what do they actually mean? Are they interchangeable, and how should the be used properly? (While we’re at it, how about “et al.”?) Thanks for helping to clear this up!
They’re not used interchangeably. I think http://www.m-w.com will give you the definitions and the full Latin names. They are abbreviations for Latin words. I.e.is Latin for “that is.” E.g. is Latin for “for example.” “Et. al.” is Latin for “and others.” Use i.e., when you are further explaining something. Use e.g., when you’re giving an example. I often see “et al” used after only one item in a series. That is not correct. Also don’t use “and et al” since that is redundant.
They’re not interchangable. Both are abbreviations for latin phrases; e.g. for exempli gratia and i.e. for id est. e.g. means “for example” and i.e. means “that is”, so you use e.g. to give examples of what you’re discussing, and i.e. to clarify what you’re discussing.
And it’s e period g period comma, and i period e period comma
etc.: Et Cetera, and so on, and other things.
i.e.: Id Est, that is. (Often used before clarification on a point.)
q.v.: Quod Vide, which see. (Used after a subject to which the reader is additionally referred.)
et al. Et Allii, Et Alia, and other people, other things.
cf.: Confer, compare. (Used to draw the reader’s attention to a point of comparrison.)
viz.: Videlicet, namely, that is to say. (Used to elaborate.)
N.B.: Nota Bene, note well, carefully.
e.g.: Exempli Gratia, for example, for instance.
c.: Circa, about, approximately.
And probably lots more.
For some reason this quote from Get Shorty got stuck in my mind (but not enough to memorize it, it was quoted on IMDB):
Ray Barboni: Let me explain something to you. Momo is dead. Which means everything he had now belongs to Jimmy Cap, including you. Which also means, when I speak, I speak for Jimmy. E.g., from now on, you start showing me the proper fuckin’ respect.
Chili Palmer: “E.g.” means “for example”. What I think you want to use is “i.e.”.
Ray Barboni: Bullshit! That’s short for “ergo”.
Chili Palmer: Ask your man.
Bodyguard: To the best of my knowledge, “e.g.” means “for example”.
Ray Barboni: E.g., i.e., fuck you! The point is this: When I say “jump”, you say “OK”, okay?
When I was a kid I remembered i.e. and e.g. this way:
i.e. = “in ether” words
e.g. = egzample
…I kinda still do!
Well, you learn something new every day!
I always thought “i.e.,” and “e.g.,” were latin abbreviations for “I’m smarter than you.”
Ok, so it should have been “e.g., in lectures at school, posts on SDMB, etc.” 
Thanks for all the help!
One more question inspired by Attrayant’s list: are “etc.” and “et al.” used differently, or are they interchangeable?
Are you sure? When referencing multiple authors, is it not correct to say (Bakunin et al., 1927)?
I don’t have any style guides here to check, but I never heard this rule before.
I’d say that that is the exact situation when you should use it.
et al is latin for “and others” so technically you could use it after just one thing, but it’s kinda vague, e.g., bananas, et al. Other what? Fruit? Yellow things? Phallic objects? Monkey food? Slippery thing?
In the law, et al is used after the first name in a series. I vaguely remember my high school english teacher telling us to cite collectively-written works of literature or criticism by the first two names and then et al, but that was a long time ago and my memory may be faulty.
I don’t think etc. and et al are interchangeable. Etc. is used specifically with things, et al primarily with people.
–Cliffy
What about Q.E.D.?
What about it? It means that which was to be proved, if that’s your question. You append that after proving a proposition, usually syllogistically or in mathematical proofs.
Quantum ElectroDynamics?
Quad Erat b]D**emonstrandum?
Come on, that’s even in Merriam-Webster’s. Doesn’t anyone do the homework anymore?
Some people don’t even re-read what they write! I did preview, but what good is that, if you don’t pay attention.
I thought everyone knew that QED means Quite Easily Done.
*Letters on his back I. N. R. I.? No: I. H. S. Molly told me one time I asked her. I have sinned: or no: I have suffered, it is. And the other one? Iron nails ran in.
—James Joyce, Ulysses
[sub]Of course, Bloom here is pondering completely erroneous explanations for the Latin initialisms he saw on the priest’s vestments. Probably no one here will need them spelled out, but just in case: Iesus Hominorum Salvator (Jesus the Savior of Men) and Iesus Nazarenus Rex Iudaeorum (Jesus of Nazareth, King of the Jews).[/sub]
I work in medical research. I use et al. every day. It’s ALWAYS used to start a list.
e.g. W.C. Cole et al. (2001) Endothelium-derived hyperpolarizing factors… *Circ.Res.*12:223-226.