He is the world, or the world is within Him, for He—glorified is He—is self-subsisting. When something self-subsisting is co-located with something else, one must indwell the other. This differs from things that are not self-subsisting, such as attributes, which may all subsist in something else.
He had no need to mention this possibility, since its invalidity is evident and no one maintains it. Everyone knows that Allah Most High is self-subsisting; He cannot belong to the category of accidents, which require a substrate in which to subsist.
The assertion, “He is neither separate nor co-located,” is of the same kind. Since its invalidity is known through clear reason, he did not include it among the alternatives. For clear reason firmly establishes that an existent is either separate from another or interpenetrating it. Ruling out these two possibilities invalidates both the position that makes Him neither separate nor interpenetrating, like something nonexistent, and the position that makes Him indwell the world, dependent on a substrate like accidents. Whatever depends on a substrate is neither self-subsisting nor independent of everything else; it therefore cannot be necessarily existent in itself.
For this reason, no rational person has maintained such a position, although some have said things that entail it. Not everyone who adopts a position accepts its implications.
He also refuted the assertion, “He is everywhere,” through another division into alternatives of this kind. For someone who maintains that He is neither within the world nor outside it cannot