"A man is a person."
Translation:Viro estas persono.
"persono" is not in the accusative here; it's a predicate subject as in German (you don't have a subject acting on an object, but a descriptor of said subject after the verb).
Why not "Viro estas persona"? doesn't the word "person" stands as an adjective here?
This grammatical construction of making non-verbs into verbs is used in Esperanto to achieve descriptive meaning (biero bongustas → biero estas bongusta, la ĉielo bluas → la ĉielo estas blua), so the sentence viro personas would most likely be interpreted as viro estas persona, that is “a man is personal”.