। ॥ १८ ॥
In plain words
That, this, like that, like this, this much, that much — whatever no such words can reach: know that as brahman. If any of them could reach it, it would be an object, and known only at second hand.
Close to the Sanskrit
That which would not become 'that', 'this', 'of that kind', 'of this kind', 'this much', 'that much', and so on — that is to be understood as brahman. If it were not so, it would become an object, and indirect as well.