What about being a Predecessor necessarily makes one a Father? Is it not perhaps possible that the Holy Spirit proceeds from the Son by a dispensational allowance on the Father's part. This would permit speaking of the Holy Spirit's procession from both the Father and the Son, while yet maintaining the ontological primacy of the Father's "fountain-ness". If we say that the Father spirates the Holy Spirit, and that the Son returns this Spirit back to the Father out of love, then the Father's spiration still holds primacy over that of the Son, and yet nevertheless the Holy Spirit still proceeds (albeit in a somewhat secondary way) from the Son.
It is entirely His nature as a Predecessor and Father that distinguishes the Father from the Son; the only way we can distinguish the persons of the Trinity is in their relationships to one another; thus, when the filioque redefines the nature of the relationships, we redefine our understanding of the Trinity from how it has been revealed to us. The Son is ontologically Son; He is not Father, or a Progenitor to the Spirit; if He was, then He would possess a similar role to the Father, and thus break the bond of unity in diversity
that characterizes the love of the Trinity. For it is in their perfect love and unity despite their ontological differences that characterizes the Unity of One God in Three persons. Thus, the Son cannot be Father or Progenitor to the Spirit; if the Spirit is returned to the Father through the Son, then we are not
speaking of His Source of being, but rather His activity in eternity, a different argument.
This idea of a "dispensational allowance" is strange; the Son has no need or ambition to duplicate the role of the Father as the Source; therefore, "dispensational allowance" would be unnecessary. Even if you argue the Son is the agent of the procession of the Spirit (as He is the agent of the creation of the world, according to Orthodox theology) - the being still comes from the Father, and thus the agent used does not contribute from His own being, nor does he add to the being, but instead acts with the being that proceeds from the Father in eternity.
Anyway, the major argument that I would have against this line of thinking (that the Son is the agent of the procession) is this: the action of the Son through time has been interaction and deification of humanity; He was the agent of Creation because He was willing to undergo self-limitation to participate in the act; this was His role, His job, as a member of the Trinity performing the will of the Trinity. He then again limited Himself to enter His very own creation and take on flesh. And He again limited Himself to allow Himself to become subject to death on the Cross as the incarnate Son.
But the nature of the Trinity, the begetting of the Son and procession of the Spirit are in the realm of God the Father; it was His nature and will that the Son be begotten and the Spirit proceed.
In any case, it can also be difficult to specifically say that the Son could have been the source or co-source through which the Spirit proceeds since it introduces the possibility of temporal difference in the actions of begetting and proceeding; can we really say that the Son was begotten before the Spirit proceeded in order to participate in the procession of the Spirit? Is that really possible before the creation of time?
We have to be careful as to how technical we want to become when speaking of the procession of the Spirit; it is hazardous to attempt to over-clarify things that cannot be contained by human logic and thought.
At best, this is merely an argument from silence. At worst, this is simply another example of Byzantine-elitism whereby we simply ignore the Latin Fathers up to the year 1054. Remember, they still were our Fathers.
No elitism here, the Fathers in the West (that I've read) make no claims of an essential procession of the Spirit from the Son. Even if you were to find one that does, it doesn't mean he is even close to right: if one guy goes agaisnt the rest of the tradition, it's safe to say he's off-base. We have had this reaction in the past to our own Eastern Fathers as well - thus, the love/hate relationship with Origen.
Another argument from silence. Neither does the Scripture explicitly deny that the Spirit proceeds from the Son. Scripture doesn't explicitly affirm a lot of things. For example, where in Scripture do you find an explicit demonstration that the Holy Spirit is an hypostasis in itself, and not simply a mode of either the Father's or Son's being (not that I believe this. I affirm the hypostaticness and consubstantiality of the Spirit for the sake of Tradition....not the sake of Scripture, for you won't find it in there)?
I'm not going to spend the time re-hashing the Orthodox arguments regarding Modalistic Monarchiansim; the Fathers answered the questions better than I, and they used the Tradition and Scripture to do so.
I feel like I'm running in circles. I ask you guys what the metaphysical danger is in affirming the Filioque, and you give me more arguments from authority. You also seem to come to non-sequitor conclusions as to what affirming the Filioque might lead to. I'm not interested in what it can lead to. Whether or not the Filioque can lead to some conclusion is neither rationally demonstrable nor empirically verifiable. I want to know what affirming the Filioque actually does......and HOW it actually does this.