Os elfos da Terra Média são mortais ou imortais?

Eles não podem morrer com a idade, mas podem morrer pela espada ou pesar.

De acordo com Tolkien, quando um Elfo se torna adulto, ele deixa de envelhecer. Eles também são menos vulneráveis a danos físicos, mas não são imortais. As vidas dos Elfos só perduram enquanto o mundo perdura.

De acordo com Wikipedia

Elves are naturally immortal, and remain unwearied with age. In addition to their immortality, Elves can recover from wounds which would normally kill a mortal Man. However, Elves can be slain, or die of grief and weariness.

Spirits of dead Elves go to the Halls of Mandos in Valinor. After a certain period of time and rest that serves as "cleansing", their spirits are clothed in bodies identical to their old ones. However, they almost never go back to Middle-earth and remain in Valinor instead. An exception was Glorfindel in The Lord of the Rings; as shown in later books, Tolkien decided he was a "reborn" hero from The Silmarillion rather than an individual with the same name. A rare and more unusual example of an Elf coming back from the Halls of Mandos is found in the tale of Beren and Lúthien, as Lúthien was the other Elf to be sent back to Middle-earth – as a mortal, however. Tolkien's Elvish words for "spirit" and "body" were fëa (plural fëar) and hröa (plural hröar) respectively.

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While the three cycles are not specifically defined, the first cycle is likely childhood and adolescence, which ended at the 100th year, the second is adulthood which could continue for Ages, and the third is for extremely old Elves; Elves did not physically age after they reached maturity, but they did age in a different sense than Men. They became ever more weary of the world and burdened by its sorrows. Elves are naturally immortal; like the Ainur, they are bound to Arda until its End. Elves are immune to all diseases, and they can recover from wounds which would normally kill a mortal Man.

Os únicos "seres inutilizáveis" no SdA são os soldados do Exército dos Mortos. O Exército dos Mortos foi amaldiçoado por Isildur com a imortalidade na forma de uma existência como esqueletos mortos-vivos depois que eles abandonaram seu juramento na Guerra da Última Aliança. Sua única chance de morrer era cumprir seu juramento.

Sim, eles são imortais até serem mortos:

As told in The History of Middle-earth and in Tolkien's Letters, Elves had a different life cycle from Men. Most of the following information strictly refers only to the Eldar, as found in his essay Laws and Customs among the Eldar, found in Morgoth's Ring.

Elves are born about one year from their conception. The day of their conception is celebrated, not the actual birthday itself. Their minds develop more quickly than their bodies; by their first year, they can speak, walk and even dance, and their quicker onset of mental maturity makes young Elves seem, to Men, older than they really are. Physical puberty comes in around their fiftieth to one hundredth year (by age fifty they reach their adult height), and by their first hundred years of life outside the womb all Elves are fully grown. Elven bodies eventually stop aging physically, while human bodies do not

Elves are naturally immortal, and remain unwearied with age. In addition to their immortality, Elves can recover from wounds which would normally kill a mortal Man. However, Elves can be slain, or die of grief and weariness. - wikipedia