でも in 国民の権利でもあれば、同時に義務でもある

Question

選挙権は国民の権利でもあれば、同時に義務でもある。

I just came across this sentence in my textbook. I notice that the sentence use "でも" instead of simply "も." What's the difference between "でも" and "も" in this context?

Answer 1

Xでもある and Xもある are different. Xでもある is Xである with も ("also") added after で. Xもある is the same as Xがある but が is replaced by も ("also").

• Xである = is X
• Xでもある = is also X
• Xがある = there is X
• Xもある = there is also X

Compare the following sentences:

• 冷蔵庫にはリンゴもあり、バナナもある。
  In the fridge, there is an apple, and there is a banana, too.
• 彼の好きな食べ物はリンゴでもあり、バナナでもある。
  His favorite food is an apple, and a banana, too.

Here the sentence wants to say "選挙権 is 国民の権利 and also 国民の義務", so でもある is the correct option.

(BTW 選挙権は国民の義務である seems to be a wrong opinion to me, but that's another story.)