Cole comments:

Would you please take a swipe at the fourth part of the prophecy: "�and either must die at the hand of the other for neither can live while the other survives.� This sentence seems crafted with great care and with such ambiguity.. Does it even mean something in and of itself, without further explanation? Could Dumbledore's interpretation be wrong?

Great question! We here at HPProgs have been hard at work analyzing this passage. The common assumption based on the text is that this means either Harry kills Voldemort or Voldemort kills Harry. But as Cole points out, the language is somewhat ambiguous. With the help of Brother Mike, HPProgs resident logician, we have come up with a logical analysis of the text, with some pretty startling conclusions.

Logically there are two parts to this prophecy: the first is "either must die at the hand of the other..." This uncommon verbiage can be unclear at first blush. Brother Mike suggests replacing "either" with the phrase "one of the two" to make it easier to understand. The new phrase reads: "one of the two must die at the hand of the other." This states that the vanquisher (Harry) must kill the Dark Lord (Voldemort) or Voldy must kill Harry.

A few quick points: First, it does not does not rule out both of them dying. It�s quite possible for Harry to kill Voldy and then at some later time die at the hand of a third person or of natural causes.

Second, this part of the prophecy doesn�t preclude the odd possibility of both dying at each other�s hand, as in a old-west-style duel in which each participant simultaneously and lethally shoots the other as he himself is about to die.

Third, if a third person�not Harry and not Voldy�does kill Harry or Voldy it will have to happen after the other one is already dead at the other�s hand. That is, in most cases while both Harry and Voldemort are alive, no one else can kill either of them. We say in most cases because there is an exception to this claim typified by the following. Suppose Voldy feeds Harry a slow acting poison that will kill Harry, but not for several weeks. In the meantime Neville kills Voldy. Neville has killed Voldy while both Harry and Voldy were alive, but still Harry is soon to die at Voldy�s hand fulfilling the prophecy. Notice that in this case Neville can not kill Harry. For if he did then neither Harry would have killed Voldy nor would Voldy have killed Harry.) Harry has been killed at Voldy�s hand; he just hasn�t died�yet.

In summary, excluding the bizarre or unusual, Harry must kill Voldemort (and then someone or something else could kill Harry) or Voldemort must kill Harry (and then someone or something else could kill Voldemort). But, neither can die by anyone else�s hand before one of them (or both of them) is killed by the other.

Very good, let us continue. The second part of the prophecy, which states "neither can live while the other survives�, is trickier than it appears. One way to try to understand this statement is to use logic. (This might get a bit technical, for those unfamiliar with the art of logic, so bear with us.)

If we let H and V stand for �Harry is alive� and �Voldemort is alive� respectively, we can write :

(H -> ~V) & (V -> ~H)

This can be thought of as stating that "Harry�s being alive implies that Voldemort is not alive, and Voldemort�s being alive implies that Harry is not alive"�which seems, at first, a fair interpretation of the prophecy. Those familiar with logic know that:

(P -> Q) <=> (~P OR Q)

(I leave proof of that as an exercise to the reader.) Using this, we can rewrite the above expression as:

(~H OR ~V) & (~V OR ~H)

which is the same as

(~H OR ~V) & (~H OR ~V)

which is the same as

~H OR ~V

i.e., either Harry is not alive or Voldy is not alive, or both are not alive.

(This simple truth table below shows that ~H OR ~V is true if and only if at least one of Harry or Voldy is not alive.)

H	V	~H	~V	~H OR ~V
T	T	F	F	F
T	F	F	T	T
F	T	T	F	T
F	F	T	T	T

One thing to note about the above interpretation: it assumes that we treat the word �survives� just the same as it would treat the phrase �is alive,� and that might not be proper because doing so already falsifies the prophecy. That is, the interpretation given above treats the prophecy as if it states "neither can live while the other is alive," clearly already not true assuming Harry is the vanquisher and Voldy is the Dark Lord because both are currently alive! Harry is clearly alive, and Voldemort more than once states that he has never died. An optional modification would be to understand the prophecy as referring to some point in the future.

Therefore we might suggest another possibility, namely that the word survives is meant to be interpreted in one of its other senses, either:

(1) To carry on despite hardships or trauma; persevere, or
(2) To live, persist, or remain usable through (some event)

Perhaps �survives� might be meant to modify something unstated (as of yet). Perhaps there is some critical, implied event, E, that either the vanquisher or the Dark Lord is not permitted to survive if the other is to live. At such time as E unfolds, it will not be the case�according to the prophecy--that both the vanquisher and the Dark Lord live through E. (Interestingly, if both are alive to experience E, then according to our analysis of the first part of the prophecy, one or the other will kill the other at the end of E.)

In conclusion, we see from this carefully and cryptically worded prophecy that, if our analysis is correct, not only must Harry kill Voldemort, or Voldemort kill Harry, but it is possible, within the logic of the wording prophecy, for both of them to be killed, as long as one of them kills the other. It also follows from our analysis that neither Harry nor Voldemort can die by another�s hand until one of them has been offed by the other. Dumbledore only told Harry that it was a kill-or-be-killed situation; he never mentioned that it might be kill-and-be-killed.

Please let us know if you find any holes in the argument. Big thanks to Brother Mike for his analysis!