Here I shall consider three criticisms. The first and most important concerns my actual argument; it comes from a Christian philosopher and fellow "filioquist" who has not stated his ecclesial affiliation. The latter two concern the filioque's dogmatic authority, and come from Orthodox believers.
I. In a post entitled "Interposition," philosopher Brandon Watson of Siris actually registers two objections to my account as outlined in "The filioque IV: the issue narrowed further." The first is that my claim that it can also be said that the Son is begotten ex Patri spirituque, "if true (I'm actually not convinced it is), would be a reductio ad absurdum of the account." The second is that, contrary to what I hold, filioquists need not reject the Cappadocian principle ('CP' for short) that every divine property must be either individual, and thus unique to a particular hypostasis, or common to all three and thus "of the nature."
On reflection, I think the second objection is right. I had taken CP to entail, in conjunction with the doctrine of the monarchy of the Father (DMF), that there is no sense in which it could be said that either the Son and the Spirit have anything to do with each other's origination from the Father as hypostases. And I had adopted that construal because the Eastern Christians with whom I have most often discussed the filioque issue do so, or at least seem to do so. But Brandon has shown why, logically speaking, one needn't construe CP as I and they have.
The upshot is this. All sides agree that the Son and the Spirit are each "God from God" (cf. St. Anselm), and thus each can be said to have the property of being God by derivation. But that is not a violation of CP; for it is equally generally agreed, as a requirement of orthodoxy, that the modes of origination of the Son and the Spirit respectively are not precisely identical. Although both "come from" the Father, who is their sole fons et origo, the Son is "begotten" and the Spirit is "spirated"; so, aside from what, exactly, that difference consists in, we must say that there is a difference. Accordingly, the fact that the Son and the Spirit each have the property of "being God from God" is only what Brandon terms a "notional" identity; in reality, the respective modes of derivation are different, and thus the modes of origination by the Father are different. So if the Son does have something to do with the Spirit's origination from the Father, the uniqueness of personal properties ad intra is preserved for the Son and the Spirit—provided that the something in question is not ekporeusis, which has already been conceded to be the unique, personal property of the Father. Following St. Gregory of Nyssa's account, Brandon labels that something as "interposition" and fleshes out a bit about what that meant for Gregory. The details of Gregory's account are interesting, but I shall not review them here. It seems to me that several possible "filioquist" accounts could observe the same stricture that Gregory's does and be at least as illuminating.
The advantage of such a result, besides its truth, is ecumenical: it does not require Eastern Christians to give up CP. I confess to feeling a bit sheepish for missing that. For the reasons Brandon gives, all the present result requires is rejecting the criticism offered by St. Photios in the Mystagogia that the filioque violates CP. And the reason why it doesn't violate CP is also a reason why it doesn't violate DMF.
By the same token, however, I can't make much sense of Brandon's other criticism of my account. My main claim has been that the Father originates the Son and the Spirit "only in relation to each other." From that, I concluded, there is a sense in which the Son is begotten ex Patri spirituque. But that is only to say that the Spirit has something to do with the Father's origination of the Son, even as the Son has something to do with the Father's origination of the Spirit; it is not to say that the sense in which the Spirit has to do with the Son's origination is the same as the sense in which the Son has to do with the Spirit's origination. Indeed, Brandon himself hints at the relevant sense of spirituque (emphasis added):
To say that the Spirit is from the Father and the Son is as much to say that the Father is together-with-the-Son in the procession of the Spirit, just as to say "Paul and Silvanus" is as much to say "Paul-with-Silvanus". This is why there is only one spiration; the spiration is always from the Father; but the Son is with the Father in the Spirit's being breathed forth by the Father, and thus distinctively interposes without detriment to the Spirit's full Godhead. The Son, on the other hand, is in being begotten together-with-the-Spirit from the Father (begotten from the Father and the Spirit), and together-with-the-Father in the Spirit's proceeding, as the only-begotten who has the same Spirit as His Father.
I don't think the boldfaced text is saying anything different from, still less incompatible with, what I've been saying. In fact, I agree with everything Brandon says. Once my mistake about CP is corrected, we're saying pretty much the same thing.
II. Now for the simpler of the two objections from the Orthodox.
In a long thread at Energetic Procession, I had written: "In fact, I do think there are problems with the filioque. E.g., I have said many times that I believe Rome needlessly wounded Church unity by inserting the phrase into the Ecumenical Creed" in AD 1014 under pressure from the "Holy Roman" Emperor. That's something I've said, in substance, many times both online and off. But a man who names himself "David" and identifies himself as a Catholic philosopher "on the verge of becoming Orthodox" objects to that as follows:
Strictly speaking, this is not a position open to a Roman Catholic, for the council of Florence declares (session 8): “In the first place, then, we give them the holy creed issued by the hundred and fifty bishops in the ecumenical council of Constantinople, with the added phrase and the Son, which for the sake of declaring the truth and from urgent necessity was licitly and reasonably added to that creed”Strictly speaking, this is not a position open to a Roman Catholic, for the council of Florence declares (session 8): “In the first place, then, we give them the holy creed issued by the hundred and fifty bishops in the ecumenical council of Constantinople, with the added phrase and the Son, which for the sake of declaring the truth and from urgent necessity was licitly and reasonably added to that creed.”
I treat that objection as "Orthodox" because it comes from somebody leaning to Orthodoxy and entails a conclusion I've heard before from some Orthodox: that Catholics cannot self-consistently affirm the truth of the filioque and the unwisdom of its addition to the Creed.
The argument itself, however, is a non-sequitur. In no sense are Catholics bound to accept the judgment that the filioque had been added to the Creed "from urgent necessity" and "reasonably." For one thing, the decree being cited had only juridical not dogmatic force. It was meant to establish only that the Council of Basel be "one" council, which indeed it became even as it was eventually moved to Florence and Ferrara. What Catholics are bound to accept, by giving the assent of faith to, is the proposition that the dogma of the filioque defined by the Council of Lyons (1274) and in due course by Florence (1442) is true. Of course I render such assent precisely as a Catholic. But that is altogether different from saying that Rome's original insertion of the phrase in 1014 was a sound move in some practical sense. Logically, one who accepts the dogmatic infallibility of general councils, and hence the truth of the filioque in particular, can affirm the former while denying the latter. That's just what I do.
III. The final objection I shall consider comes from—who else?—Perry Robinson, and is that, by Roman standards themselves, the council held at Constantinople in 879-80 binds Rome. Among other things, that council forbade any attempt to "add" to the ecumenical creed of 381; and historically, the the filioque is the only candidate for such addition. This issue has come up before between Perry and me; here, I link to the latest iteration of it.
There are two difficulties with his objection: one historical, one logical. The historical has been cited deftly by Greg DeLassus (emphasis added):
In his work The Photian Schism, Francis Dvornik [a Jesuit—ML] quotes the letter which Pope John VIII sent to Patriarch Photios wherein he recognizes Photios as Patriarch and the Constantinopolitan synod of 879-80 as a legitimate ecumenical council rescinding the synod of 869-70.
Basically, in his letter, John accepts Photios and his council conditionally. John intructed that his legates should insist on certain assurances from Photios. If his conditions (including that Photios acknowledge Roman supremacy) are met, then the council is accepted. If his conditions are not met, then the council is rejected. So, were John’s conditions accepted by Photios and the Constantinopolitan church? We have no letter in reply from Photios to John which would make his acceptance explicit. As such, given that John’s reception of the 879 synod is conditional on such acceptance, we cannot say with any precision that Rome did or did not receive the 879 synod as authoritative.
The relevant text of the letter reads: Nam et ea, quae pro causa tuae restitutionis synodali decreto Constantinopoli misericorditer acta sunt, recipimus. Si forasse nostri legati in eadem sinodo contra apostolicam preceptionem egerint, nos nec recipimus nec iudicamus alicuius existere firmitatis.
Now given that Rome eventually repudiated said council, we may conclude that in due course she judged the conditions not to have been met. Hence, the council can be said to have bound Rome only if one asumes that its authority obtained with or without Rome's consent. Catholics as such cannot accept that assumption. And given the broader issues between Catholicism and Orthodoxy, such an assumption would only beg the question against the former.But even supposing, for argument's sake, that Rome really had accepted the council of 879-880, there remains the logical question whether the condemnation of adding anything to the confession embodied in the Nicene-Constantinopolitan Creed of 381 ('NCC' for short) is dogmatically binding by Rome's own standards. That would indeed be the case if the condemnation entails that the filioque is, in fact, false, or otherwise adds anything of substance. But the pertinent conciliar text entails no such result. In the translation and with the emphasis Perry uses, here's the most pertinent passage:
If one dares to rewrite another Symbol besides this one, or add to it, or subtract from it, or to remove anything from it, and to display the audacity to call it a Rule, he will be condemned and thrown out of the Christian Confession. For to subtract from, or to add to, the holy and consubstantial and undivided Trinity shows that the confession we have always had to this day is imperfect. It condemns the Apostolic Tradition and the doctrine of the Fathers. If one, then having come to such a point of mindlessness as to dare do what we have said above, and set forth another Symbol and call it a Rule, or to add to or subtract from the one which has been handed down to us by the first great, holy and Ecumenical Synod of Nicaea, let him be Anathema.
The key thing to note about that is its conditionality. Its condemnation extends to the filioque only if it be granted that the doctrine of the filioque "adds to the holy and consubstantial and undivided Trinity" and thus shows that the earlier confession is "imperfect." But that is precisely what Rome does not grant.
The position of the Catholic Church is that the filioque does not "add" to the doctrine of the Trinity as developed by councils acknowledged as ecumenical by East and West. The Roman claim is that the phrase filioque merely helps to make explicit what was implicit in NCC, the "symbol" being referred to by the above condemnation. But it follows that the "confession" embodied in NCC is "imperfect" only if Rome's later adding the filioque to NCC implies that she holds there is something wrong with the confession NCC embodied when it was issued in 381. No such implication holds, nor does Rome think it does. NCC was a perfectly adequate and orthodox response to the issues of its time, and its original text remains perfectly true. It just doesn't say everything true that later contingencies might call for saying. Now as I've said before, I believe that Rome's later judgment that the filioque was worth adding to NCC was pastorally unsound. But that doesn't affect the question of the truth of the doctrine expressed by that phrase.
As always, the key issue lurking in the background here is that of "development of doctrine." In a spirit quite similar to that of certain Catholic traditionalists and Protestant fundamentalists, Perry and some other Orthodox deny that there is any legitimate DD. I shall shortly resume addressing that issue in its own right.