See this online text:

See also the texts listed on the page God and Christ and on the post ‘Online text: “On the Procession of the Holy Spirit”, by Msgr. John F. McCarthy‘; as well as the following texts and ebooks:

A. By Catholic Authors: Explanations and Positive Theology

  • Ending the Byzantine Greek Schism; Containing: The 14th c. Apologia of Demetrios Kydones for Unity with Rome & the ‘Contra Errores Graecorum’ of St. Thomas Aquinas, edited by James Likoudis (New Rochelle, NY: Catholics United for the Faith, 1992), with Imprimatur. May be purchased on this page of James Likoudis’ page and at Amazon.
  • “Filioque” by Anthony Maas. The Catholic Encyclopedia, Vol. 6 (New York: Robert Appleton Company, 1909). May be read online on this page of New Advent.
  • On the Holy Trinity [De Trinitate, Libri XV], by St. Augustin [Bishop St. Augustine of Hippo], translated by Arthur West Haddan, revised and annotated, with an introductory essay, by Professor W.G.T. Shedd. In A Select Library of the Nicene and Post-Nicene Fathers, edited by Dr. Philip Schaff, Volume III. St. Augustin: On the Holy Trinity; Doctrinal Treatises; Moral Treatises (Buffalo: Christian Literature Company, 1887): pp. 1-228. May be read online, and available in pdf, mobi, epub, and other formats at Internet Archive, and at Online Library of Liberty. Also available at Google Play Books
    • The text as republished in Nicene and Post-Nicene Fathers, First Series, Volume 3, edited by Philip Schaff (Buffalo, NY: Christian Literature Publishing Co., 1887) may be read online and is available in pdf, mobi, epub, and other formats at Christian Classics Ethereal Library. The text, sans preface and notes, may be read online on this page of Catholic Culture (copyright © 2021 Trinity Communications) and on this page of New Advent (copyright © 2020 by Kevin Knight).
    • The original translation is also available: On the Trinity, [by Bishop St. Augustine of Hippo,] translated by Arthur West Haddan. Volume VII of The Works of Aurelius Augustine, Bishop of Hippo: A New Translation, edited by Marcus Dods (Edinburgh: T.&T. Clark, 1873). May be read online, and available in pdf, mobi, epub, and other formats at Internet Archive, with a 2nd copy at Internet Archive. Also available at Google Play Books.
  • [The Person of the Holy Ghost], by Saint Thomas Aquinas, O.P., in the Summa Theologica, First Part, QQ 36-38. May be read online at New Advent: Question 36, Question 37, and Question 38.

B. By Catholic Authors: Ecumenical Perspectives

  • “The Filioque: What Is at Stake?”, by Dr. Avery Cardinal Dulles, S.J., Concordia Theological Quarterly, Volume 59, Number 1 (1995): pp. 31-47. The entire volume is available in pdf format at Concordia Theological Seminary. [Caution: Persons without both adequate theological formation and the state of sanctifying grace are counselled to avoid essays in the volume other than those of Cardinal Dulles, as the volume itself is an issue of a non-Catholic journal.]
  • “The Greek and Latin Traditions regarding the Procession of the Holy Spirit”, by the Pontifical Council for Promoting Christian Unity, L’Osservatore Romano, Weekly Edition in English, 20 September 1995, page 3. May be read online on this page of the EWTN Library. Under the title “The Father as the Source of the Whole Trinity: The Procession of the Holy Spirit in Greek and Latin Traditions”, from Catholic International (January 1996), pages 36-43, the text is available on this page of Catholic Culture. The text is also appended to “The Church Fathers and the Filioque” by Joe Gallegos (1998), which may be read online on this page of Catholic Fidelity.com (Joseph A. Gallegos © 1998 All Rights Reserved).
  • “St. Augustine’s Theology of the Holy Trinity”, by Rev. Dr. Yves Cardinal Congar, O.P.. May be read on the post “Augustine, the Trinity, and the Filioque” at Crossroads Initiative, which states that it is ‘an excerpt from Yves Congar’s book “I Believe in the Holy Spirit”’.

C. By Catholic Authors: Explorations or Speculative Theology

  • “Eternal Happening: God as an Event of Love”, by Prof. Rev. Antonio López, F.S.C.B., Ph.D., Communio, Volume 32.2 (Summer 2005): pp. 214-245. Available in pdf format through this page of Communio.
  • The Father’s Spirit of Sonship: Reconceiving the Trinity, by Rev. Dr. Thomas G. Weinandy, O.F.M., Cap. (Eugene, OR: Wipf and Stock Publishers, 2011). The ebook and the printed book may be purchased at Barnes & Noble. The printed book may be purchased at Amazon.
  • “The ‘Filioque’: Beyond Athanasius and Thomas Aquinas: An Ecumenical Proposal” by Rev. Dr. Thomas G. Weinandy, O.F.M., Cap., in Ecumenical Perspectives on the Filioque for the 21st Century, edited by Myk Habets (London, New York: Bloomsbury T&T Clark, 2014): pp. 185-197. The ebook and printed text of the larger work is available at Bloomsbury.
  • “God the Father: A Beginning Without Beginning”, by Prof. Rev. Antonio López, F.S.C.B., Ph.D., Communio, Volume 36.2 (Summer 2009). Available in pdf format through this page of Communio.
  • “The Holy Spirit as the Mutual Love of the Father and the Son”, by David Coffey, Theological Studies 51 (1990), pp. 195. Available in pdf format at Theological Studies. [Caution: Persons without both adequate theological formation and the state of sanctifying grace are counselled to avoid other essays on the website, as some of them appear to depart from the received Tradition or are liable to misunderstanding by the faithful.]

D. By Non-Catholic Authors (Read with caution.)

  • On the Clause “and the Son” in Regard to the Eastern Church and the Bonn Conference: A Letter to the Rev. H.P. Liddon, by the Rev. E.B. Pusey (Oxford: James Parker & Co.; London, Oxford, Cambridge: Rivingtons; New York: Pott, Young & Co., 1876). May be read online, and available in pdf, mobi, epub and other formats at Internet Archive with a 2nd copy at Internet Archive. [Read with prayerful caution, as this work is written by the great Dr. Pusey from a non-Catholic perspective.]
  • A Short Explanation of the Nicene Creed, for the Use of Persons Beginning the Study of Theology, by Alexander Penrose Forbes (Oxford and London: Parker & Co., 1866): pages 256–263, at Internet Archive. [Read with prayerful caution, as this work is written from a non-Catholic perspective.]

On the Memorial of Saint Paulinus II of Aquileia in the Ordinary Form of the Roman Rite (calendar of Slovenia) and in advance of the Memorial of Saint Benedict Biscop in the Personal Ordinariate of the Chair of Saint Peter. For other texts and ebooks, you may access the List of Free eBooks (Arranged by Title), the List of Free eBooks (Grouped by Subject), the List of Worth-It Catholic Books & eBooks, and the main page of the Catholic eBooks Project.

“But when he, the Spirit of truth, is come, he will teach you all truth… All things whatsoever the Father hath are mine. Therefore, I said, that he shall receive of mine, and will shew it to you.” (St. John xvi, 13-15)