# Does "Either must die at the hand of the other" imply both that A can only be killed by B and that B can only be killed by A?

The prophesy made by Professor Trelawney about Harry Potter includes the phrase "Either must die at the hand of the other", speaking of Harry and Lord Voldemort.

Does this mean that both Voldemort must be killed by Harry and Harry must be killed by Voldemort?

Or merely that one must be killed by the other?

If the former, then presumably Harry is immortal after Voldemort's death.

• Either = one of them; Other = the other one. Your logic is faulty: after the death of one, the other simply continues to live his life until he dies. Commented Sep 11, 2020 at 16:39
• @Greybeard no faulty logic, just asking which is the meaning -- so you're saying it is the latter case, i.e. one must be killed by the other as 'either' means one of them. That makes sense to me. Commented Sep 11, 2020 at 16:53
• @Greybeard Your comment is surely a reasoned answer? Apart from the minor and almost venial fault of attributing flawed logic to what is merely a supposition. I have accordingly voted up. Commented Sep 11, 2020 at 17:05

As a pronoun, either has a meaning of "one or the other of two people or things" (Lexico). In the sentence, the contrast is between one of them and the other one: one must die at the hand of the other. Logically, this gives two mutually exclusive possibilities:

• Voldemort must die at the hand of Harry
• Harry must die at the hand of Voldemort

Once one of these possibilities happens, the prophecy is fulfilled: either has died at the hand of the other.

The alternative interpretation you give that requires both possibilities to be true would require a different initial pronoun, e.g. both:

• Both must die at the hand of the other.

Or better yet:

• Both must die at the hand of each other.

In math logic, A OR B statement can True in three cases:
(1) A is True and B is False
(2) B is True and A is False
(3) A and B is True

If “Either” means: one OR the other of two people or things, then "Either must die at the hand of the other" could be true in the case that both will die at the hand of each other. This is similar to the case (3) above. This prophecy admits a few ways of being fulfilled but in the HP series the third option is chosen.

• I think, though, that in the archaic diction being used in this quoted sentence, "either" essentially means "each." Commented Oct 21, 2021 at 7:41