If an adjective ends in an "o," you change it to an ___a___ before adding the adverbial ending.

I know the answer BUT why is it a?

Question

If an adjective ends in an "o," you change it to an ___a___ before adding the adverbial ending.

I know the answer BUT why is it a?

anonymous · Answer

So far as I know, we change it to an A simply because that's just how the language is built. 

I really can't think of any special reasons for why we would change the O to an A, 
anymore than I can think of a reason for why we add LY onto the end of our adjectives, in English.

anonymous · Answer

InYourHead is right as far as I know. Latin languages like Portuguese, Spanish and Italian have adjectives ending in 'o' in the masculine case and 'a' in the feminine case in most cases.