accents in MOUSA

[John]

Why is the circumflex accent used in the nom pl of the first declension feminine noun MOUSA (Muse), e.g.,
Mousai with circumflex over the penultimate dipthong -ou, and then the acute accent is used in the dat pl, e.g., Mousais with acute over the penultimate dipthong? Does -ai count as short, but -ais count as long?

[annis]

Does -ai count as short, but -ais count as long?

Yes. Final -[face=spionic]ai[/face], the first declension nominative plural counts as short when you determine the accent. The same is true of final -[face=spionic]oi[/face], the second declension nominative plural.

Final -[face=spionic]ai[/face] in verbs is often short for accent, too. The exception is the optative mood, which you'll not see until quite a few more lessons have passed.

And welcome to Textkit.