Quote Originally Posted by Throbert McGee View Post
Also, есть is particularly likely to be used if the subject and predicate are the same: A есть А ("A is A," if you were translating Atlas Shrugged into Russian, God help you), or Мальчик есть мальчик ("A boy is a boy", in the sense of "It's a boy's nature to act like a boy", which can also be expressed with Мальчик мальчиком, putting the predicate in the instrumental.)
Is that last bit sort of like Boys "will be" boys, with the will be omitted. As I know that Быть in the past or future causes the nominal predicate to decline to the instrumental case? right?