La diferencia entre "aun" y "aún"

Question

aun - even

aún -1. still (con afirmación); yet, still (con negación)

   2. even  (incluso)

These are the definitions I got, but the two words still seem pretty hard to differentiate.

Is there an easy way to tell the difference between the two, or are they just used the same way interchangeably?

Also are the pronunciations different? If I remember right, "aun" has the stress on the "a". Is this right?

Answer 1

The RAE has the following to say about this issue:

ORTOGR. Escr. con acento cuando pueda sustituirse por todavía. Aún ('todavía') está enfermo. En los demás casos, se escribirá sin tilde. Te daré 100 duros, y aun ('hasta') 200, si los necesitas. No tengo yo tanto, ni aun ('ni siquiera') la mitad.

It is written with accent when it can be substituded by "todavía". Otherwise it's written without tilde.

Pronunciation stays the same, by the way. - Gekkosan, May 11, 2010

I thought that since "a" is a strong vowel, and "u" is a weak vowel, when put together the "a" would get the stress, unless a tilde was put over the weak vowel. Not that it makes that much of a difference in this case. - bmancornelious, May 15, 2010