1 If, again, they declare that these things [below] are a shadow of those [above], as some of them are bold enough to maintain, so that in this respect they are images, then it will be necessary for them to allow that those things which are above are possessed of bodies. For those bodies which are above do cast a shadow, but spiritual substances do not, since they can in no degree darken others. If, however, we also grant them this point (though it is, in fact, an impossibility), that there is a shadow belonging to those essences which are spiritual and lucent, into which they declare their Mother descended; yet, since those things [which are above] are eternal, and that shadow which is cast by them endures for ever, [it follows that] these things [below] are also not transitory, but endure along with those which cast their shadow over them. If, on the other hand, these things [below] are transitory, it is a necessary consequence that those [above] also, of which these are the shadow, pass away; while; if they endure, their shadow likewise endures.
2. If, however, they maintain that the shadow spoken of does not exist as being produced by the shade of [those above], but simply in this respect, that [the things below] are far separated from those [above], they will then charge the light of their Father with weakness and insufficiency, as if it cannot extend so far as these things, but fails to fill that which is empty, and to dispel the shadow, and that when no one is offering any hindrance. For, according to them, the light of their Father will be changed into darkness and buried in obscurity, and will come to an end in those places which are characterized by emptiness, since it cannot penetrate and fill all things. Let them then no longer declare that their Bythus is the fullness of all things, if indeed he has neither filled nor illuminated that which is vacuum and shadow; or, on the other hand, let them cease talking of vacuum and shadow, if the light of their Father does in truth fill all things.
3. Beyond the primary Father, then— that is, the God who is over all— there can neither be any Pleroma into which they declare the Enthymesis of that Æon who suffered passion, descended (so that the Pleroma itself, or the primary God, should not be limited and circumscribed by that which is beyond, and should, in fact, be contained by it); nor can vacuum or shadow have any existence, since the Father exists beforehand, so that His light cannot fail, and find end in a vacuum. It is, moreover, irrational and impious to conceive of a place in which He who is, according to them, Propator, and Proarche, and Father of all, and of this Pleroma, ceases and has an end. Nor, again, is it allowable, for the reasons already stated, to allege that some other being formed so vast a creation in the bosom of the Father, either with or without His consent. For it is equally impious and infatuated to affirm that so great a creation was formed by angels, or by some particular production ignorant of the true God in that territory which is His own. Nor is it possible that those things which are earthly and material could have been formed within their Pleroma, since that is wholly spiritual. And further, it is not even possible that those things which belong to a multiform creation, and have been formed with mutually opposite qualities [could have been created] after the image of the things above, since these (i.e., the Æons) are said to be few, and of a like formation, and homogeneous. Their talk, too, about the shadow of kenoma— that is, of a vacuum— has in all points turned out false. Their figment, then, [in what way soever viewed,] has been proved groundless, and their doctrines untenable. Empty, too, are those who listen to them, and are verily descending into the abyss of perdition.
Source: Adversus haereses (New Advent)