I thought that the grave mark meant that a vowel was pronounced where it otherwise wouldn’t be, like “séance”. But in “résumé”, the first e is pronounced the same as in “resume”, so why does it have a mark over it?
First, it’s not an accent grave, it’s an accent aigu (the accent grave goes down into the grave; clever, n’est pas?). The first accent aigu is to let you know how it’s pronounced-like the “ay” in “eight.” Without the accent it would sound like the e in “angel.” The one at the end is to let you know that it has that sound, and is pronounced (e’s at the end of words without accents are silent).
é has an acute mark.
è has a grave mark.
I think that the acute e is prononced like a long A, like in way or play or touché. I don’t know why it’s not pronounced like that in résumé, but I do know that resumé is a valid alternate spelling.
But even so, it’s not pronounced like the first e in resume. That has a long e sound (EE), not a short e (EH).
résumé takes an acute (not grave) accent over both Es (if we choose to include French diacriticals) because that is how it occurs in French. That is probably because it is a back-formation from the French participle résumer, where the accent ensures that a later syllable does not accidentally get the stress, as happens in many (most) three syllable French verbs.
Okay, right, in case you weren’t aware, this word comes from the French word for summarized. (And the French word for acute is aigu.) I guess the pronunciation changed when English adopted the word, but not the spelling. Why, I don’t know. Here’s a job-hunting tip from The Onion this week that might help you out:
No, the diacritic mark that does that job is the diaeresis, as in naïve, Zoë or Citroën.