The Western gloss on oikonomia, as summarized by Tertullian in Ch. 8 of Against Praxeas:
If any man from this shall think that I am introducing some probolh -- that is to say, some prolation of one thing out of another, as Valentinus does when he sets forth AEon from AEon, one after another -- then this is my first reply to you: Truth must not therefore refrain from the use of such a term, and its reality and meaning, because heresy also employs it. The fact is, heresy has rather taken it from Truth, in order to mould it into its own counterfeit. Was the Word of God put forth or not? Here take your stand with me, and flinch not. If He was put forth, then acknowledge that the true doctrine has a prolation; and never mind heresy, when in any point it mimics the truth. The question now is, in what sense each side uses a given thing and the word which expresses it. Valentinus divides and separates his prolations from their Author, and places them at so great a distance from Him, that the AEon does not know the Father: he longs, indeed, to know Him, but cannot; nay, he is almost swallowed up and dissolved into the rest of matter. With us, however, the Son alone knows the Father, and has Himself unfolded "the Father's bosom." He has also heard and seen all things with the Father; and what He has been commanded by the Father, that also does He speak. And it is not His own will, but the Father's, which He has accomplished, which He had known most intimately, even from the beginning. "For what man knows the things which be in God, but the Spirit* which is in Him?" But the Word was formed by the Spirit*, and (if I may so express myself) the Spirit* is the body of the Word. The Word, therefore, is both always in the Father, as He says, "I am in the Father;" and is always with God, according to what is written, "And the Word was with God;" and never separate from the Father, or other than the Father, since "I and the Father are one." This will be the prolation, taught by the truth, the guardian of the Unity, wherein we declare that the Son is a prolation from the Father, without being separated from Him. For God sent forth the Word, as the Paraclete also declares, just as the root puts forth the tree, and the fountain the river, and the sun the ray. For these are probolai, or emanations, of the substances from which they proceed. I should not hesitate, indeed, to call the tree the son or offspring of the root, and the river of the fountain, and the ray of the sun; because every original source is a parent, and everything which issues from the origin is an offspring. Much more is (this true of) the Word of God, who has actually received as His own peculiar designation the name of Son. But still the tree is not severed from the root, nor the river from the fountain, nor the ray from the sun; nor, indeed, is the Word separated from God. Following, therefore, the form of these analogies, I confess that I call God and His Word -- the Father and His Son -- two. For the root and the tree are distinctly two things, but correlatively joined; the fountain and the river are also two forms, but indivisible; so likewise the sun and the ray are two forms, but coherent ones. Everything which proceeds from something else must needs be second to that from which it proceeds, without being on that account separated: Where, however, there is a second, there must be two; and where there is a third, there must be three. Now the Spirit indeed is third from God and the Son; just as the fruit of the tree is third from the root, or as the stream out of the river is third from the fountain, or as the apex of the ray is third from the sun. Nothing, however, is alien from that original source whence it derives its own properties. In like manner the Trinity, flowing down from the Father through intertwined and connected steps, does not at all disturb the Monarchy, whilst it at the same time guards the state of the Economy.
[* As I noted in my earlier post, "Spirit as Divine Substance," the usage of the term spiritus in these cases refers to the divine substantia, not the Person of the Holy Spirit.]
Note the contrast here between Tertullian's characteristically Stoic idea of probole and the Neoplatonic notion of "emanation," with which it could easily be confused. I'll explain how that distinction plays out in more detail in the near future, as well as how it relates to Tertullian's use of the term "form" (forma) in the description above.
