I'm reading Familia Romana book and encountered these 2 sentences.

Corsica et Sardinia insulae magnae sunt.


Brundisium et Sparta oppida magna sunt.

Why does the ae changes to a and vice versa?


1 Answer 1


In Latin, nouns belong to different groups, which are called declensions. The word insula is of the first declension, whereas the word oppidum is of the second declension. Each declension has its own endings. In addition, oppidum is neuter.

Neuter words of the second declension have a singular ending -um, plural -a; words of the first declension have a singular ending on -a, and a plural on -ae. That's why it is one oppidum, two oppida; but one insula, two insulae.

By the way, the fact that both oppida (plural) and insula (singular) end on -a is best considered coincidental in the present context.

  • Is there a context in which the shared -a is more than coincidental?
    – BThompson
    Commented Apr 14, 2021 at 12:39
  • 1
    @BThompson Interesting question! I am far from well-informed about this, someone else will be able to provide better references.... but I found discussion in this thread: forum.wordreference.com/threads/… and in this article: Rovai, F. (2012). Between Feminine Singular and Neuter Plural: Re-Analysis Patterns. Transactions of the Philological Society, 110(1), 94–121. onlinelibrary.wiley.com/doi/epdf/10.1111/… Commented Apr 14, 2021 at 15:23
  • 1
    @BThompson The answer to this question latin.stackexchange.com/questions/2132/… by TKR also gives a relevant example relating Latin pilus "hair" and pila "ball". Commented Apr 14, 2021 at 15:35
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    @BThompson: I think the neuter plural and feminine -a are thought to have been related in Proto-Indo-European, the neuter -a being originally an abstract collective suffix. I'm not sure how well established this theory is.
    – Cerberus
    Commented Apr 14, 2021 at 16:46
  • Interesting, thank you both!
    – BThompson
    Commented Apr 14, 2021 at 16:57

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