FSA (first declension) question

[tbjohnston]

Is there any way to tell from the standard form of the noun (singular nominative, singular genitive ending, pronoun) whether the FSA ending is ην vs. αν?

For example:
Standard Form__________Accusative Singular
βουλή, ῆς, ἡ _____________βουλήν θεά, ᾶς, ἡ ______________θεάν θάλασσα, ης, ἡ ___________θάλασσαν

Thank you

(Apologies if this has already been asked & answered):

[annis]

This is one of those situations where paying attention to vowel length matters. The short-alpha -αν ending will only happen when the nominative ending is also a short alpha. In the case of θάλασσα we know from the accent that the final vowel must be short, or the accent couldn't be where it is. In other situations you'll have to pay close attention to your dictionary.

I think you'll see the short-alpha nom/acc. most often in the participles.