Existem muitos fantasmas em Arda
Os termos "wraith", "wight" e "ghost" são um pouco intercambiáveis. Pelo menos, eles não foram usados consistentemente por Tolkien. Vamos ignorar os Espectros do Anel, pois eles parecem ser um caso único de "nem mortos nem vivos", estando ligados ao Anel.
Almas sem corpos
Um "fantasma" no Arda seria um feä ("alma") sem um hroä ("corpo"). Normalmente, um feä não estaria apenas perambulando por aí. No caso de um elfo, seria nos salões de Mandos. Não se sabe onde o feä dos homens vai.
É importante saber que uma vez que um feä seja desdobrado, Mandos apenas convoca para seus corredores. Essa convocação pode ser recusada. Embora fosse raro, enquanto Melkor e Sauron estavam em Arda, parece ter se tornado mais frequente nesta "era dos homens":
But it would seem that in these after-days more and more of the Elves, be they of the Eldalie in origin or be they of other kinds, who linger in Middle-earth now refuse the summons of Mandos, and wander houseless in the world, unwilling to leave it and unable to inhabit it, haunting trees or springs or hidden places that once they knew.
The History of Middle-earth Volume 10: Morgoth's Ring, The Later Quenta Silmarillion (II), p. 223
Sem Casais e Lingerers
Parece haver uma diferença entre um elfo que "morre" e outro que "desvanece":
On the one hand, the Houseless, rebels at least against the Rulers, and maybe even deeper under the Shadow; on the other, the Lingerers, whose bodily forms may no longer be seen by us mortals, or seen only dimly and fitfully. [...]
Moreover, the Lingerers are not houseless, though they may seem to be. They do not desire bodies, neither do they seek shelter, nor strive for mastery over body or mind.
The History of Middle-earth Volume 10: Morgoth's Ring, The Later Quenta Silmarillion (II), p. 224
Assim, um Houseless seria um feä que recusasse a convocação para os Halls of Mandos e um Lingerer seria um Elf que se tornasse " sombras e memórias ". Os Lingerers também são referidos em O Silmarillion :
In after days, when because of the triumph of Morgoth Elves and Men became estranged, as be most wished, those of the Elven-race that lived still in Middle-earth waned and faded, and Men usurped the sunlight. Then the Quendi wandered in the lonely places of the great lands and the isles, and took to the moonlight and the starlight, and to the woods and caves, becoming as shadows and memories, save those who ever and anon set sail into the West and vanished from Middle-earth.
The Silmarillion, Of Men, p. 117
Comunicação
Nem todos esses fantasmas são pacíficos:
Some are filled with bitterness, grievance, and envy. Some were enslaved by the Dark Lord and do his work still, though he himself is gone. They will not speak truth or wisdom. To call on them is folly. To attempt to master them and to make them servants of one own's will is wickedness. Such practices are of Morgoth; and the necromancers are of the host of Sauron his servant.
The History of Middle-earth Volume 10: Morgoth's Ring, The Later Quenta Silmarillion (II), p. 224
Comunicar-se com um fantasma também é perigoso, já que alguns deles estão buscando desesperadamente um novo corpo:
Some say that the Houseless desire bodies, though they are not willing to seek them lawfully by submission to the judgement of Mandos. The wicked among them will take bodies, if they can, unlawfully. The peril of communing with them is, therefore, not only the peril of being deluded by fantasies or lies: there is peril also of destruction.
ibid.
Ver um feh
Finrod fala sobre ver um feä em uma discussão com Andreth:
'Men say various things, be they Wise or no,' said Andreth. 'Many hold that there is but a single thing: the body, and that we are one of the beasts, though the latest come and the most cunning. But others hold that the body is not all, but contains some other thing. For often we speak of the body as a "house", or as "raiment", and that implies an indwelling, though of what we speak in uncertainty.
'Among my folk men speak mostly of the "breath" (or the "breath of life" ), and they say that if it leaves the house, it may by seeing eyes be seen as a wraith, a shadowy image of the living thing that was.'
'That is but a guess,' said Finrod, 'and long ago we said things similar, but we know now that the Indweller is not "breath" (which the hroä uses), and that seeing eyes cannot see one that is houseless, but that the living eyes may draw from the feä within an image which the houseless conveys to the housed: the memory of itself.'
The History of Middle-earth Volume 10: Morgoth's Ring, Athrabeth Finrod ah Andreth, p. 352
Então parece que você normalmente não pode ver um feh a menos que transmita uma imagem de si mesmo para você.
Gorlim
O único exemplo que encontrei de um "fantasma" seria Gorlim, que conversou com Beren em um sonho. Gorlim foi morto por Sauron antes.
Then Beren was aware in his dream of a form that came to him across the water, and it was a wraith of Gorlim; and it spoke to him declaring his treachery and death, and bade him make haste to warn his father.
The Silmarillion, Of Beren and Lúthien, p. 191
Tolkien dedicou algum tempo à "comunicação de pensamento" no Ósanwe-kenta , onde ele diz que uma combinação de urgência do remetente e passividade no receptor facilitaria a transmissão do pensamento:
Urgency is imparted by great need of the "sender" (as in joy, grief or fear); and if these things are in any degree shared by the "receiver" the thought is the clearer received. [...]
These causes may strengthen the thought to pass the veils and reach a recipient mind. But that mind must remain open, and at the least passive. If, being aware that it is addressed, it then closes, no urgency or affinity will enable the sender's thought to enter.
Ósanwe-kenta
Como Beren estava dormindo e Gorlim queria avisá-lo de um ataque iminente, isso parece provável. Embora o Ósanwe-kenta apenas fale sobre feär , é possível que o feä
De qualquer forma, embora seja comunicação com um "fantasma", não encontrei textos sobre ver um.