Qui Ex Patre Filioque Procedit?

Any and every textbook treatment of Catholic-Orthodox division puts the filioque high on the list of issues driving the two apart. In the last fifteen years, however, great strides have been made, and many no longer regard this issue as church-dividing.There are at least three important texts to consider here:

1) The 1995 clarification issued by Rome, available here. The pope asked for this to be published when the Ecumenical Patriarch visited him in June of that year for the Church of Rome's patronal feast. Met. John (Zizioulas) of Pergamon has commented on that document here.

2) The 2003 declaration of the North American Orthodox-Catholic dialogue, available here.

3) John Zizioulas, Lectures on Christian Dogmatics, where he says (as Kallistos Ware and other Orthodox theologians have before him) that "understood in the right way, we may indeed accept the filioque." He notes that we cannot talk about a filioque in the eternal Trinity because the Father is sole cause of the Spriit. But the Greek Fathers allow for a role for the Son in the procession of the Holy Spirit. This is clearest in St. Gregory of Nyssa's That There Are Not Three Gods.

Now we have a new work out from Oxford University Press that gives an overview of this whole debate:

A. Edward Siercinski, The Filioque: History of a Doctrinal Controversy (Oxford Studies in Historical Theology) (Oxford, 2010), 368pp.

This looks to be a very major and substantial work, and I asked the Orthodox historian Dr. Robert Haddad, Sophia Smith Professor Emeritus of History at Smith College in Northampton, MA, who has published on the filioque, to review this for us in Logos in 2011.