aun vs. aún

[Robie]

I'm having a battle against my teacher about these two words. According to the dictionaries that I have, they have these two words listed separately - both of them having similar meanings of 'yet' or 'even' but the entries seem to indicate a different usage without actually specifying what that might be.

Has anyone run across a "rule" that might help me understand first whether there really is a difference or whether these are interchangable? And if there is a difference, how do I know when to use one instead of the other.

Thanks,
Robie

[sendai]

Native speakers have no end of trouble with these two words, and they constantly mix them up. For that reason, if you get them wrong few people will notice or care.

I have a rule that works well for native speakers, but I don't know if it will help you. Here's the rule: If you can substitute "todavía", then it's "aún" with the tilde. Otherwise, it's not. ("Aun" without the tilde can generally be substituted with "incluso", but that's not part of this rule.) I believe this rule works in 100% of the cases.

For non-native speakers it's more difficult, but this might help you:

aun
even except in comparisons
aunque
aun cuando
aun si
aun así
ni aun

aún
still/yet
even only in comparisons (aún más, aún mejor, aún menos, etc.)

[Robie]

Thanks! I'll digest this a little and see if I can apply it after I have more time to let it sink in.