2 For the first exercise of that [power] respecting anything, is styled Ennœa; but when it continues, and gathers strength, and takes possession of the whole soul, it is called Enthymesis. This Enthymesis, again, when it exercises itself a long time on the same point, and has, as it were, been proved, is named Sensation. And this Sensation, when it is much developed, becomes Counsel. The increase, again, and greatly developed exercise of this Counsel becomes the Examination of thought (Judgment); and this remaining in the mind is most properly termed Logos (reason), from which the spoken Logos (word) proceeds. But all the [exercises of thought] which have been mentioned are [fundamentally] one and the same, receiving their origin from Nous, and obtaining [different] appellation according to their increase.
Just as the human body, which is at one time young, then in the prime of life, and then old, has received [different] appellations according to its increase and continuance, but not according to any change of substance, or on account of any [real] loss of body, so is it with those [mental exercises]. For, when one [mentally] contemplates anything, he also thinks of it; and when he thinks of it, he has also knowledge regarding it; and when he knows it, he also considers it; and when he considers it, he also mentally handles it; and when he mentally handles it, he also speaks of it.
But, as I have already said, it is Nous who governs all these [mental processes], while He is himself invisible, and utters speech of himself by means of those processes which have been mentioned, as it were by rays [proceeding from Him], but He himself is not sent forth by any other.
Source: Adversus haereses (New Advent)