My own belief about the
half-elven, and this isn't written anywhere that I know of, just what I believe, is that they have fëar not bound to
Arda as the
elves do, but like elves they have a greater control over their body with their fëar. And when a half-elf gets to choose which
race to be counted among, his fëa would become bound to the world or not, depending upon his choice.
fëa - this is the elves' word meaning somthing very much like "spirit". Fëar is the plural form.
If a baby
elf gets his fëa from
Iluvatar but it is nourished also by his parents, then this could explain why an half-elf could have a spirit not bound to Arda, but still have something extra which allows the half-elven to live a longer life than
men, even before making the big choice. Fëa nourished by an elf (or two half elves).
Why did
Elros ever weary of life, and age faster than elves eventually, and especially why did he die much younger than
Elrond's children had lived to be before making their choice?
In Laws and Customs we learn that the Eldar believe the fëar of all elves come from
Eru. In the earlier days elves thought otherwise; that both body and fëa comes from the parents, but some disagreed saying that as elves grow up they show some character trait that is new, not of their parents. But more still they decided this could not be because if it were, then 'rebirth' would be an injustice as it would deprive the parents of half of their input - the fëa half. Now, this latter reason is tricky to me, because
Tolkien later dropped 'rebirth' and went with 'rehousing', therefore this can not have been the reasoning of the elves. All the same it is made clear that the Eldar believe that fëar come from Eru.
rebirth - the return of a deceased elf via birth
rehousing - the return of an elf directly into a body identical to his former, so the above mentioned injustice would not exist here, even if elf fëa came originally from parents and not Eru.
In this theory, a half-elf (Elros) who decides to be counted a man and has a human wife, would produce children with fëa not bound to Arda, and with a much smaller amount of
elvish nourishment of the fëa. I say small amount, because in theory the half-elf who decided to be a man would still have that extra elvish kick to his fëa and so he may provide a little to his children. These children would reallybe men with perhaps a notably longer life span, but not that elvish mastery over the body with spirit, as did the half-elven acording to my belief.
Laws and customs also tells us that both parents (father no less than mother) nourish the fëa of their child. Also, both parents pass strength of mind and body into their children. But it must be the mother passes more strength in body (mind? doubt it, but am unsure), since we also learn that females have less strength (and speed) after bearing children.
They Eldar also hold that a greater part of their strength goes forth in the begetting and bearing of children, that does with men.
So in my theory, the children of Elrond would have had more elvish nourishment of the fëa than Elros had, since he came of two half-elves, rather than an half-elf and an elf. Since my theory also says that it is the elvish nourishment of the fëa not bound to Arda (the half-elven), which allows them to live longer than men, this could explain why Elros passes at a younger age than Elrond's childern were at when they made their choice.
The problem that I can't explain so well to myself is why Elladan and Elrohir feared the dead. This mostly because I can't understand why the men feared the dead as much as they did. Perhaps there is something in the Letters about this?
But if we just chalk it up to being a spiritual thing, then I will guess that men fear the dead since their own
spirits are not bound to the world (though I am still not sure why this should be). This being so, and according to my theory, I would say that the half-elven who had not yet made their choice, would fear the dead because they have spirits not bound to Arda.
There is a quote from Letters (which I do not have, but it is used in that debate that
Ancalagon linked to above) saying that Elladan and Elrohir's choice is not told, and that they delayed their choice for some time (paraphrasing - watch out!
). But to me this seems to clearly mean that at the time of the Paths of the Dead, they hadn't made their choice.
In theory, Elrond for example, would not have feared the dead.
So my belief is that his sons feared the dead, not because they were half-elven, but because they were half-elves that had not chosen to be counted as elves yet.
