Truth in eidolons

Before dissolving into nothingness, the aquastor Malrubius in CITADEL said he and Triskele were "beings created and sustained by the power of the imagination and the concentration of thought." He went on to say, "The machine [on the Hierodule ship, which had departed via the Corridors of Time] looked among your memories and found us. Our lives in your mind are not so complete as those of Thecla and the old Autarch, but we are there nevertheless, and live while you live. But we are maintained in the physical world by the energies of the machine, and its range is but a few thousand years." B, F & O said much the same thing about eidolons while in Apu's tomb in URTH, explaining that mighty Tzadkiel had revived the Severian killed in the fall on the Ship by using "remembrance taking [taken?] from your dead mind to build your mind and you anew." That's easy enough to grant mighty Tzadkiel. And B, F & O had a machine on their craft to do the job of looking into dead Apu's head to make the new eidolon of Severian they were talking to. That's okay, too. They also explained that the eidolon of Severian created by Tzadkiel went on to eventually achieve independent physical substantiality by eating, breathing and the like. Then they faded into the past. That's still okay, so long as they didn't travel too far into the past for the machine on their craft to sustain his new body. But Severian soon escaped from the tomb and went far into the future, to the beach on Ushas. Why didn't he dissolve to nothingness, like Malrubius? We were led to believe that after the New Sun arrived he lost most of his supernatural powers. What sustained his body on Ushas long enough for it to achieve substantiality? Aquastor Malrubius had imparted certain information to Severian, including "The Key to the Universe". If, as both Malrubius and the Hierodules claimed, an eidolon's mind is created from the mind of another, then where does the eidolon's knowledge come from if not the mind of the person it was created from? How could the eidolon of Malrubius know anything not known to Severian? Godel would not approve. -Roy

Severian was an unusual fellow, and his eidolon bulked up more quickly than most. It's also possible that B, F & O didn't know everything about eidolons (2 of them being youngsters, and the other one a not very intelligent robot).

Eidolons must be able to acquire and store additional information after they are created, or they wouldn't be able to carry on a conversation, or otherwise interact. The eidolon of Malrubius must have learned "The Key to the Universe" at some point after being created, but before dissolving.

It's arguable that the newly-breathing Apu Punchau left behind was the eidolon, while "Severian" was actually the "original". Or, it could be that when the light of the White Fountain restored his ability to traverse the Corridors, it also restored his flesh.

IIRC, eidolons were used by intelligent machines to communicate with and teach uneducated people. It's simple to see that an eidolon-projector takes appearances and behaviors from the minds of the audience, but the subject matter comes from the operator.