5 Then, again, their first and first-begotten Ogdoad will be overthrown as follows: They must admit that Bythus and Sige, Nous and Aletheia, Logos and Zoe, Anthropos and Ecclesia, do individually dwell in the same Pleroma. But it is impossible that Sige (silence) can exist in the presence of Logos (speech), or again, that Logos can manifest himself in the presence of Sige. For these are mutually destructive of each other, even as light and darkness can by no possibility exist in the same place: for if light prevails, there cannot be darkness; and if darkness, there cannot be light, since, where light appears, darkness is put to flight. In like manner, where Sige is, there cannot be Logos; and where Logos is, there certainly cannot be Sige. But if they say that Logos simply exists within (unexpressed), Sige also will exist within, and will not the less be destroyed by the Logos within. But that he really is not merely conceived of in the mind, the very order of the production of their (Æons) shows.
Source: Adversus haereses (New Advent)