I'll admit that my memory of the arguments presented in the thread is fuzzy, but I do remember Azzy bringing up a quote from The Dunwich Horror that attributes Yog-Sothoth as all-encompassing and all-knowing:
"Yog-Sothoth knows the gate. Yog-Sothoth is the gate. Yog-Sothoth is the key and guardian of the gate. Past, present, future, all are one in Yog-Sothoth. He knows where the Old Ones broke through of old, and where They shall break through again. He knows where They have trod earth’s fields, and where They still tread them, and why no one can behold Them as They tread." ~The Dunwich Horror
This happens to be consistent with what Randolph Carter realizes when Yog-Sothoth confronts him:
"It was an All-in-One and One-in-All of limitless being and self—not merely a thing of one Space-Time continuum, but allied to the ultimate animating essence of existence’s whole unbounded sweep—the last, utter sweep which has no confines and which outreaches fancy and mathematics alike. It was perhaps that which certain secret cults of earth have whispered of as YOG-SOTHOTH, and which has been a deity under other names; that which the crustaceans of Yuggoth worship as the Beyond-One, and which the vaporous brains of the spiral nebulae know by an untranslatable Sign—yet in a flash the Carter-facet realised how slight and fractional all these conceptions are." ~Through the Gates of the Silver Key
Also of note is that this is stated to come from a passage of the Necronomicon, which also has instructions on how to summon Yog-Sothoth:
"“More space, Willy, more space soon. Yew grows—an’ that grows faster. It’ll be ready to sarve ye soon, boy. Open up the gates to Yog-Sothoth with the long chant that ye’ll find on page 751 of the complete edition, an’ then put a match to the prison. Fire from airth can’t burn it nohaow.”" ~The Dunwich Horror
"Almost eight feet tall, and carrying a cheap new valise from Osborn’s general store, this dark and goatish gargoyle appeared one day in Arkham in quest of the dreaded volume kept under lock and key at the college library—the hideous Necronomicon of the mad Arab Abdul Alhazred in Olaus Wormius’ Latin version, as printed in Spain in the seventeenth century. He had never seen a city before, but had no thought save to find his way to the university grounds; where, indeed, he passed heedlessly by the great white-fanged watchdog that barked with unnatural fury and enmity, and tugged frantically at its stout chain. Wilbur had with him the priceless but imperfect copy of Dr. Dee’s English version which his grandfather had bequeathed him, and upon receiving access to the Latin copy he at once began to collate the two texts with the aim of discovering a certain passage which would have come on the 751st page of his own defective volume." ~The Dunwich Horror
As well as instructions on how to communicate with 'Umr at-Tawil:
"A moment later Carter knew that this was so, for the Shape had spoken to his mind without sound or language. And though the name it uttered was a dreaded and terrible one, Randolph Carter did not flinch in fear. Instead, he spoke back, equally without sound or language, and made those obeisances which the hideous Necronomicon had taught him to make. For this Shape was nothing less than that which all the world has feared since Lomar rose out of the sea and the Winged Ones came to earth to teach the Elder Lore to man. It was indeed the frightful Guide and Guardian of the Gate—’Umr at-Tawil, the ancient one, which the scribe rendereth the Prolonged of Life." ~Through the Gates of the Silver Key
Based on the above things, it is clear that the Necronomicon is a credible source, although there are some inaccuracies to be found- for example, this excerpt:
"“And while there are those,” the mad Arab had written, “who have dared to seek glimpses beyond the Veil, and to accept HIM as a Guide, they would have been more prudent had they avoided commerce with HIM; for it is written in the Book of Thoth how terrific is the price of a single glimpse. Nor may those who pass ever return, for in the Vastnesses transcending our world are Shapes of darkness that seize and bind. The Affair that shambleth about in the night, the Evil that defieth the Elder Sign, the Herd that stand watch at the secret portal each tomb is known to have, and that thrive on that which groweth out of the tenants within—all these Blacknesses are lesser than HE Who guardeth the Gateway; HE Who will guide the rash one beyond all the worlds into the Abyss of unnamable Devourers. For HE is ’UMR AT-TAWIL, the Most Ancient One, which the scribe rendereth as THE PROLONGED OF LIFE.”" ~Through the Gates of the Silver Key
The author (Abdul Alhazred) talks at length about how the Ancient Ones are these malevolent forces that cannot be trusted, but Randolph Carter realizes how childish of a notion this is:
"The Guide knew, as he knew all things, of Carter’s quest and coming, and that this seeker of dreams and secrets stood before him unafraid. There was no horror or malignity in what he radiated, and Carter wondered for a moment whether the mad Arab’s terrific blasphemous hints, and extracts from the Book of Thoth, might not have come from envy and a baffled wish to do what was now about to be done. Or perhaps the Guide reserved his horror and malignity for those who feared." ~Through the Gates of the Silver Key
"Damnation, he reflected, is but a word bandied about by those whose blindness leads them to condemn all who can see, even with a single eye. He wondered at the vast conceit of those who had babbled of the malignant Ancient Ones, as if They could pause from their everlasting dreams to wreak a wrath upon mankind. As well, he thought, might a mammoth pause to visit frantic vengeance on an angleworm." ~Through the Gates of the Silver Key
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Anyway, despite the Necronomicon accurately articulating Yog-Sothoth's boundlessness and even providing ritualistic gestures and chants related to him, Abdul Alhazred still treats Azathoth as the ruler of all things. There are a few references to Azathoth being in the Necronomicon:
"He must meet the Black Man, and go with them all to the throne of Azathoth at the centre of ultimate Chaos. That was what she said. He must sign in his own blood the book of Azathoth and take a new secret name now that his independent delvings had gone so far. What kept him from going with her and Brown Jenkin and the other to the throne of Chaos where the thin flutes pipe mindlessly was the fact that he had seen the name “Azathoth” in the Necronomicon, and knew it stood for a primal evil too horrible for description." ~The Dreams in the Witch House
"There were suggestions of the vague, twilight abysses, and of still vaster, blacker abysses beyond them—abysses in which all fixed suggestions of form were absent. He had been taken there by the bubble-congeries and the little polyhedron which always dogged him; but they, like himself, had changed to wisps of milky, barely luminous mist in this farther void of ultimate blackness. [...] Eventually there had been a hint of vast, leaping shadows, of a monstrous, half-acoustic pulsing, and of the thin, monotonous piping of an unseen flute—but that was all. Gilman decided he had picked up that last conception from what he had read in the Necronomicon about the mindless entity Azathoth, which rules all time and space from a curiously environed black throne at the centre of Chaos." ~The Dreams in the Witch House
"The legend of Yig, Father of Serpents, remained figurative no longer, and I started with loathing when told of the monstrous nuclear chaos beyond angled space which the Necronomicon had mercifully cloaked under the name of Azathoth." ~The Whisperer in Darkness
The second thing explicitly describes Azathoth as the ruler of all time and space, which is further backed up by certain other quotes:
"Out in the mindless void the daemon bore me, Past the bright clusters of dimensioned space, Till neither time nor matter stretched before me, But only Chaos, without form or place. Here the vast Lord of All in darkness muttered Things he had dreamed but could not understand, While near him shapeless bat-things flopped and fluttered In idiot vortices that ray-streams fanned. They danced insanely to the high, thin whining Of a cracked flute clutched in a monstrous paw, Whence flow the aimless waves whose chance combining Gives each frail cosmos its eternal law. “I am His Messenger,” the daemon said, As in contempt he struck his Master’s head." ~Fungi from Yuggoth
"Before his eyes a kaleidoscopic range of phantasmal images played, all of them dissolving at intervals into the picture of a vast, unplumbed abyss of night wherein whirled suns and worlds of an even profounder blackness. He thought of the ancient legends of Ultimate Chaos, at whose centre sprawls the blind idiot god Azathoth, Lord of All Things, encircled by his flopping horde of mindless and amorphous dancers, and lulled by the thin monotonous piping of a daemoniac flute held in nameless paws." ~The Haunter of the Dark
"The passage through the vague abysses would be frightful, for the Walpurgis-rhythm would be vibrating, and at last he would have to hear that hitherto veiled cosmic pulsing which he so mortally dreaded. Even now he could detect a low, monstrous shaking whose tempo he suspected all too well. At Sabbat-time it always mounted and reached through to the worlds to summon the initiate to nameless rites. Half the chants of the Sabbat were patterned on this faintly overheard pulsing which no earthly ear could endure in its unveiled spatial fulness. Gilman wondered, too, whether he could trust his instinct to take him back to the right part of space. How could he be sure he would not land on that green-litten hillside of a far planet, on the tessellated terrace above the city of tentacled monsters somewhere beyond the galaxy, or in the spiral black vortices of that ultimate void of Chaos wherein reigns the mindless daemon-sultan Azathoth?" ~The Dreams in the Witch House
Meanwhile, Yog-Sothoth is identified with all time and space:
"Then, in the midst of these devastating reflections, Carter’s beyond-the-gate fragment was hurled from what had seemed the nadir of horror to black, clutching pits of a horror still more profound. This time it was largely external—a force or personality which at once confronted and surrounded and pervaded him, and which in addition to its local presence, seemed also to be a part of himself, and likewise to be coexistent with all time and coterminous with all space. There was no visual image, yet the sense of entity and the awful concept of combined localism, identity, and infinity lent a paralysing terror beyond anything which any Carter-fragment had hitherto deemed capable of existing." ~Through the Gates of the Silver Key
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With all of this out of the way, I still can't give a concrete answer as to how Yog-Sothoth and Azathoth compare to each other. An agreement will be reached sooner or later, but for now, I want you guys to draw your own conclusions based on everything I just said in this post and in my last few posts on the other thread.