1 In this regard, Marcus Plested’s Orthodox Readings of Aquinas (Oxford: Oxford University Press, 2015) is certainly of note. See also idem, “ ‘Light from the West’: Byzantine Readings of Aquinas,” in Orthodox Constructions of the West (ed. George E. Demacopoulos and Aristotle Papanikolaou; New York: Fordham University Press, 2013) 58–70; idem, “Aquinas in Byzantium,” in The Cambridge Intellectual History of Byzantium (ed. Anthony Kaldellis and Niketas Siniossoglou; Cambridge: Cambridge University Press, 2017) 542–56; John Demetracopoulos, “The Influence of Thomas Aquinas on Late Byzantine Philosophical and Theological Thought: À propos of the ‘Thomas de Aquino Byzantinus’ Project,” Bulletin de philosophie médiévale 54 (2012) 101–24. There are also a number of other articles in The Cambridge Intellectual History of Byzantium (ed. Kaldellis and Siniossoglou) that highlight the importance of Western sources in Byzantium and other aspects of Byzantine history and thought relevant to this present study.

2 Some treatments of Kalekas’s work are available, however: see Plested, Orthodox Readings of Aquinas, 114–19. See also idem, “Aquinas in Byzantium,” 549–50. In addition, the work of Claudine Delacroix-Besnier is also noteworthy, providing important insight into Kalekas’s relationship with other Byzantine unionists (Claudine Delacroix-Besnier, “Manuel Calécas et les Frères Chrysobergès, grecs et prêcheurs,” Actes des congrès de la Société des historiens médiévistes de l’enseignement supérieur public 32.1 [2001] 151–64). Concerning Kalekas’s biography, the work of Raymond Loenertz is still the most extensive. In particular, Loenertz’s critical edition of Kalekas’s letters (1950) includes an introduction to his life and works, incorporating material from Loenertz’s work on the letters and other research (Raymond Loenertz, Correspondance de Manuel Calecas [StT 152; Vatican City: Biblioteca Apostolica Vaticana, 1950]). See also Raymond Loenertz, “Manuel Calécas, sa vie et ses oeuvres d’après ses lettres et ses apologies inédites,” Archivum Fratrum Praedicatorum 17 (1947) 195–207. Some other sources from early 20th cent. scholarship also deal with Kalekas’s theology and its relationship to Western sources. See, for example, Jean Gouillard, “Les influences latines dans l’oeuvre théologique de Manuel Calécas,” Échos d’orient 37 (1938) 36–52. Other relevant sources are cited in the following pages.

3 In addition to De fide, Kalekas authored a number of other systematic works, liturgical tracts, and polemical works. Aside from Loenertz’s edition of his letters, almost none of Kalekas’s works are available in a critical edition. The exception to this is Adversus Iosephum Bryennium, which Giovanni Mercati edited in 1931: Notizie di Procoro e Demetrio Cidone, Manuele Caleca e Teodoro Metileniota. Ed altri appunti per la storia della teologia e della letteratura bizantina del secolo XIV (StT 56; Vatican City: Biblioteca Apostolica Vaticana, 1931) 454–73. The textual editions of Kalekas’s other works are as follows: Contra errores Graecorum (Version latine d’Ambroise Traversari; ed. P. Stevartius; Ingolstadt 1608; PG 152:13–258); De essentia et operatione (ed. F. Combefis; Bibliothecae Graecorum Patrum Auctarium novissimum; Paris, 1672; PG 152:283–428); De processione Spiritus Sancti (PG 154:864–958); Expositio missae in Nativitate Domini iuxta ritum Ambrosianum, in Sposizione della Messa che si canta nella festa della Natività di Cristo secondo la tradizione di Santo Ambrogio. Dal Latino tradotta in Greco da Demetrio Cidonio (ed. A. Fumagalli; Milan, 1757). See Loenertz, Correspondance de Manuel Calecas, v.

4 In his seminal work on this subject, Martin Jugie mentions Kalekas’s Contra Graecorum numerous times, basing his assessment of Kalekas’s teaching largely on this text; see Martin Jugie, De Processione Spiritus Sancti ex fontibus Revelationis et secundum Orientales dissidentes (Rome: Istituto Grafico Tiberino, 1936) 332–34; see also 171, 234, 240, 252. Jugie also mentions Kalekas’s De processione in Jugie, De Processione Spiritus Sancti, 334 n. 1. Concerning modern secondary scholarship on De fide itself, few modern studies engage the content of this text directly. Plested does offer a summary of De fide as part of a wider treatment of the influence of Aquinas on Kalekas. On the subject of the Trinity, Plested emphasizes parallels between the text of De fide and Aquinas’s Summa contra gentiles (Plested, Orthodox Readings of Aquinas, 115–17). In this he follows Gouillard, whose work on Kalekas’s Latin sources is notable (“Les influences latines,” 36–52). See also Plested, “Aquinas in Byzantium,” 549–50. The text of De fide deque principiis catholicae fide employed here, which appears in Migne’s Patrologia Graeca (1863), originally appeared in 1698 as part of The Book of Charity Against the Latins. See Τόμος ἀγάπης κατὰ Λατίνων (Jassy, 1698) 413–90. This text was reprinted in PG 152:429–662. See John Meyendorff, “Eglises-soeurs. Implications ecclésiologiques du Tomos Agapis,” Istina 20 (1975) 35–46. Textually, however, De fide stands in need of a modern critical edition. Migne’s reprinting does not engage with the manuscript tradition before 1698.

5 For example, Kalekas’s De processione is not only a postconversion text but is explicitly organized as a defense of Western trinitarian theology (Gouillard, “Les influences latines,” 38). For similar reasons, Plested notes the theological importance of Kalekas’s De fide as an authentically Byzantine text (Plested, Orthodox Readings of Aquinas, 117).

6 Gouillard, “Les influences latines,” 36–52. See also Plested, Orthodox Readings of Aquinas, 116. See n. 31 below.

7 Loenertz, Correspondance de Manuel Calecas, 17–18. For an overview of Byzantine theology during this period, see Gerhard Podskalsky, Theologie und Philosophie in Byzanz. Der Streit um die theologische Methodik in der spätbyzantinischen Geistesgeschichte (14./15.Jh.), seine systematischen Grundlagen und seine historische Entwicklung (Byzantinisches Archiv 15; Munich: Beck, 1977) 173–230.

8 Claudine Delacroix-Besnier, “Conversions constantinopolitaines au XIV^e siècle,” Mélanges de l’École française de Rome–Moyen-Age 105 (1993) 747.

9 Norman Russell, “Palamism and the Circle of Demetrius Cydones,” Porphyrogenita: Festschrift für Julian Chrysostomides (ed. E. Harvarlia-Crook and J. Herrin; Aldershot: Ashgate, 2003) 154.

10 Loenertz, Correspondance de Manuel Calecas, 18.

11 See Plested, Orthodox Readings of Aquinas, 1, 115; Loenertz, “Manuel Calécas, sa vie et ses oeuvres,” 200. In 1305, some extracts from the Summa theologiae were made available in Greek translation by Bernard de Gaillac. Antoine Dondaine, “Contra Graecos. Premiers écrits polémiques des Dominicains d’Orient,” Archivum Fratrum Praedicatorum 21 (1951) 320–446, at 325–27; Giovanni Mercati, Notizie di Procoro e Demetrio Cidone, Manuele Caleca e Teodoro Metileniota ecc., 11; Plested, Orthodox Readings of Aquinas, 66.

12 Judith R. Ryder, The Career and Writings of Demetrius Kydones: A Study of Fourteenth-Century Byzantine Politics, Religion and Society (Leiden: Brill, 2010) 17.

13 Concerning the Tertia pars, only questions 1, 45, 54, and 55 are known to have appeared in Greek translation. John A. Demetracopoulos, “The Sitz im Leben of Demetrius Cydones’ Translation of Pseudo-Augustine’s Soliloquia,” Quaestio 6 (2006) 191–258, at 226–27.

14 Ryder, Career and Writings of Demetrius Kydones, 17 n. 82. In this, Ryder relies on the research of S. G. Papadopoulos, Ἑλληνικαὶ μεταφράσεις Θωμιστιχῶν ἔργων (Athens: Φιλεχπαιδευτιχή Ἑταιρεία, 1967) 43, and elsewhere. Demetrios’s brother, Prochoros Kydones, aided in this translation of the Summa theologiae, including articles from the Tertia pars and supplement. Ryder, Career and Writings of Demetrius Kydones, 17 n. 83.

15 Delacroix-Besnier, “Conversion constantinopolitaines au XIVe siècle,” 747. Loenertz, Correspondance de Manuel Calecas, 18.

16 Loenertz, Correspondance de Manuel Calecas, 22.

17 Plested, Orthodox Readings of Aquinas, 115. See Loenertz, “Manuel Calécas, sa vie et ses oeuvres,” 200. See also Loenertz, Correspondance de Manuel Calecas, 20–22. Gouillard, “Les influences latines,” 43–46.

18 Plested, Orthodox Readings of Aquinas, 118–19. Raymond Loenertz, “Les dominicains byzantins Théodore et André Chrysobergès et les négociations pour l’union des Églises grecque et latine de 1415 à 1430,” Archivum Fratrum Praedicatorum 9 (1939) 5–61, at 8.

19 Kalekas and Maximos were in contact in 1403 and for some time after that. Loenertz, Correspondance de Manuel Calecas, 32; see also 38, 40.

20 Loenertz, “Manuel Calécas, sa vie et ses oeuvres,” 201–2; idem, Correspondance de Manuel Calecas, 24.

21 Loenertz, Correspondance de Manuel Calecas, 25.

22 Ibid., 18; for the text of this apology, see appendix 1, 308–18. At the same time (Autumn, 1396) Kalekas wrote a second apology addressed to those ecclesiastics who had made themselves his adversaries (ibid., appendix 2, 318–21). There are also fragments of a third apology from the same period (ibid., appendix 3, 321–23).

23 Around 1398, Kalekas wrote another text, De essentia et operatione Dei, which was specifically opposed to the theology of Gregory Palamas. Claudine Delacroix-Besnier, Les Dominicains et la chrétienté grecque aux XIV ^e et XV ^e siècles (Rome: École Française de Rome, 1997) 267.

24 Loenertz, Correspondance de Manuel Calecas, 30. Delacroix-Besnier, Les dominicains et la chrétienté grecque, 267.

25 Loenertz, Correspondance de Manuel Calecas, 42.

26 Nickiphoros I. Tsougarakis, The Latin Religious Orders in Medieval Greece, 1204–1500 (Medieval Church Studies 18; Turnhout: Brepols, 2012) 205. See also Loenertz, “Manuel Calécas, sa vie et ses oeuvres,” 195–207. Kalekas also translated many Latin works into Greek, a list of which can be found here: John Demetracopoulos, “Manuel Kalekas’ Translation of Boethius’ De Trinitate: Introduction, New Critical Edition, Index Latinograecitatis,” Synthesis Philosophica 20 (2005) 85–118, at 86.

27 PG 152:430a–31b.

28 For the purposes of this study, we will focus our analysis on the doctrine of trinitarian procession found in the third chapter of De fide (PG 152:473d–529a).

29 See Aquinas, SCG 1.1.

30 See ibid., 4.1–14, 53–55, et al. Compare this structure with that of his treatment of the same material in ST III^a q. 1–26.

31 Gouillard, “Les influences latines,” 44. Plested, Orthodox Readings of Aquinas, 116.

32 PG 152:476d.

33 Aquinas, ST I^a q. 27, a. 1, co.

34 PG 152:476d–77a. The language of πρόσωπα (rather than ὑπόστασις) may indicate another point of Latin influence. There is some precedent for juxtaposing Arius and Sabellius in this way in the Cappadocians as well. For example, see Gregory of Nyssa, Κατὰ Ἀρείου καὶ Σαβέλλιου, Gregorii Nysseni Opera (GNO) (ed. Fredrick Mueller; 3 vols.; Leiden: Brill, 1958) 3.1:71–85.

35 PG 152:477a.

36 Aquinas, ST I^a q. 27–43 deals with the Trinity in itself. While the same doctrine is effectively taught in the Contra gentiles, Aquinas structures his argument differently there; see SCG 4.2–49.

37 Aquinas, SCG 4.10.7 could be a partial exception to this—this text lists objections to the doctrine of divine procession and generation and gives Arianism and Sabellianism as examples of opposing errors that concern the unity of the divine essence. However, the broader structural context still seems to point toward the Summa theologiae as an important influence in this regard. For example, although Aquinas opposes Arianism and Sabellianism here, he does use causality to illustrate their errors. Likewise, although Aquinas treats the errors of Photius, Sabellius, and Arius as trinitarian heresies in the Contra gentiles, he does not use the concept of causality to characterize these positions as false approaches to the concept of trinitarian procession; see SCG 4.4–7.

38 See Aquinas, ST I^a q. 27, a. 4, ad 1; see also Aquinas’s arguments against Arianism in ST I^a q. 27, a. 1, co.

39 PG 152:476d–77a.

40 “God is therefore one substance, three persons: Father, Son, Holy Spirit. And we confess the Father to be the cause of the Son and the Holy Spirit, and the Son and the Holy Spirit to be caused. For from him [the Father], the Son is by begetting, and the Holy Spirit by proceeding. Thence, with the Son and the Spirit referring back to the Father as to one cause, we think the one God is three when considered among themselves, but each is God when contemplated according to himself” (PG 152:477a; translation mine). Ἡ αἰτία and its grammatical variants have a broad semantic field in classical Greek, and differences between the scholastic use of “causa” and use of αἴτιον in 14th-cent. Byzantium cannot detain us here. However, both Aristotle and Plato specifically use the term in a causal sense. See Plato, Tim. 68e, Phaed. 97a, Resp. 464b; see Aristotle, Phys. 194b16, Metaph. 983a26. See LSJ, s.v. αἴτιον, τό; αἰτία, ἡ; αἴτιος, α, ον; et al. Αἴτιον also appears as “cause” or “source” in the New Testament and in the Septuagint; for example, see Heb 5:9; Macc 4:47, 13:4. A Greek-English Lexicon of the New Testament and Other Early Christian Literature: A Translation and Adaptation of Walter Bauer’s Griechisch-Deutsches Wörterbuch zu den Schriften des Neuen Testaments und der übringen urchristlichen Literatur (4th ed.; Chicago: University of Chicago Press, 1957), s.v. αἴτιος, α, ον. See also A Patristic Greek Lexicon (ed. G. W. H. Lampe; Oxford: Clarendon Press, 1961), s.v. αἰτία, ἡ and αἴτιος. Kalekas will continue to apply the language of causality to the internal relations of the trinitarian persons in the fourth book of De fide, which articulates a version of the psychological analogy (PG 152:541a).

41 See text in n. 40 above. The Greek text of the creed that appears in the first Council of Constantinople uses ἐκπορευόμενον to describe what in the Latin text appears as the “processio” of the Holy Spirit. Decrees of the Ecumenical Councils (ed. Norman Tanner; 2 vols.; Washington, DC: Georgetown University Press, 1990) 1:24 ln. 26–28. See also A Patristic Greek Lexicon (ed. Lampe), s.v. ἐκπορευτός, ἐκπορευτῶς, ἐκπορεύω.

42 “That the Holy Spirit proceeds from the Father through the Son is taught from the first to the seventh synod . . . Tarasios, most holy patriarch of Constantinople, convened the seventh synod, with a letter containing a profession of the right faith from the bishops of the East: ‘we believe also, in the Holy Spirit, who proceeds (ἐκπορευόμενον) from the Father through the Son, and is himself revealed to be God’ ” (PG 152:508b). Kalekas is referring to the acts of the council, which records a profession of faith sent by clergy from Antioch, Alexandria, and elsewhere to Patriarch Tarasius of Constantinople that describes the procession (ἐκπορευόμενον) of the Spirit from the Father through the Son. “Concilium Nicaenum II: Actio Tertia,” in Sacrorum Conciliorum Nova et Amplissima Collectio (ed. Joannes Mansi; 53 vols.; Florence: 1766) 12:1122d. (Tanner’s Decrees of the Ecumenical Councils does not reproduce this version of the Creed, instead referring the reader to the Nicene-Constantinopolitan creed; see Decrees of the Ecumenical Councils [ed. Tanner], 1:134.) The council documents, prefaced by a historical introduction, can be found in Sacrorum Conciliorum Nova (ed. Mansi), 12:951–1154.

43 See A. Edward Siecienski, The Filioque: History of a Doctrinal Controversy (New York: Oxford University Press, 2010) 147–48. Nilus Kabasilas (d. 1363), who taught Demetrios Kydones, had argued strongly against the filioque, despite his student’s strong sympathy for Aquinas. Plested, Orthodox Readings of Aquinas, 96–100. See Nilus Cabasilas, Sur le Saint-Esprit (ed. Théophile Kislas; Paris: Cerf, 2001). For a study of Nilus’s engagement with Aquinas’s pneumatology, see Nilus Cabasilas et theologia S. Thomae de processione Spiritus Sancti (ed. Emmanuel Candal; ST 116; Città del Vaticano: Biblioteca apostolica vaticana, 1945).

44 Kalekas, Contra errores Graecorum, I, IV (PG 152:187–212). Jugie, De Processione, 234. Gouillard, “Les influences latines,” 38. See n. 5 above.

45 “The Holy Spirit exists from the substance of the Father and the Son, which the Church of the Romans asserts, saying that he proceeds (ἐκπορεύεσθαι) from both” (De unione 2 [PG 141:17c]). Concerning the nature of this procession, in De unione 9 Bekkos argues that causality (αἰτίαν) can be used to describe the procession of the Son from the Father, and the Spirit from both the Father and the Son. However, because all that belongs to the Son originates from the Father as first cause, it is not necessary, absolutely speaking, to ascribe two independent processional causes to the Spirit (both the Father and the Son). De unione 9 (PG 141:25c).

46 See Christopher Beeley, “Divine Causality and the Monarchy of God the Father in Gregory of Nazianzus,” HTR 100 (2007) 199–214. Joseph Lienhard, “Ousia and Hypostasis: The Cappadocian Settlement and the Theology of ‘One Hypostasis,’ ” in Trinity: An Interdisciplinary Symposium on the Trinity (ed. Stephen Davis, Daniel Kendal, and Gerald O’Collins; New York: Oxford University Press, 2002) 99–121. For a recent study of Gregory of Nazianzus, see Andrew Hofer, Christ in the Life and Teaching of Gregory of Nazianzus (Oxford: Oxford University Press, 2013). For a discussion of the connection between causality and divine paternity in Aquinas and Gregory Nazianzus, see John Baptist Ku, “Divine Paternity in the Theology of Ss. Gregory Nazianzen and Thomas Aquinas,” in Thomas Aquinas and the Greek Fathers (ed. Michael Dauphinais, Andrew Hofer, and Roger Nutt; Ave Maria, FL: Sapientia Press of Ave Maria University, 2019) 110–29. See also idem, “Divine Spiration in the Theology of Ss. Gregory Nazianzen and Thomas Aquinas,” The Thomist 86.3 (2022): 373–415. Gregory of Nyssa’s That There Are Not Three Gods appeared around the year 390, and develops the distinction between ousia and hypostasis using the language of causality (GNO 3.1:55–57). Gregory states explicitly that he does not intend the use of causality in this context to diminish the immutability of the divine nature in any way. Gregory argues that only the difference between the cause itself and the one that is from the cause can provide the necessary distinction between persons in the Trinity (GNO 3.1:56–57. For a discussion of this text and its implications, see Lewis Ayres, “On Not Three Gods: Gregory of Nyssa’s Trinitarian Theology,” in Nicaea and Its Legacy: An Approach to Fourth-Century Trinitarian Theology (Oxford: Oxford University Press, 2004) 344–63.

47 See De unione 9 (PG 141: 25c). Peter Gilbert shows the degree to which Bekkos is reliant on Basil of Caesarea in this text (Peter Gilbert, “Not an Anthologist: John Bekkos as a Reader of the Fathers,” Communio 36 [2009] 259–304, at 285–87). After the Council of Lyon concluded in 1274, Bekkos worked for the acceptance of the council in Byzantine circles (Donald M. Nicol, The Last Centuries of Byzantium, 1261–1453 [New York: Cambridge University Press, 1993] 61–65). Bekkos’s De Unione attempts to argue for the legitimacy of the union achieved at Lyon to a Byzantine audience. Although the exact date of this text is not known, it was likely authored between 1275 and 1280. See Alexandra Riebe, Rom in Gemeinschaft mit Konstantinopel. Patriarch Johannes XI. Bekkos als Verteidiger der Kirchenunion von Lyon (1274) (Mainzer Veröffentlichungen zur Byzantinistik 8; Wiesbaden: Harrassowitz, 2005) 123. For other uses of αἴτιος in the context of trinitarian procession by the Cappadocians and other patristic authors, see A Patristic Greek Lexicon (ed. Lampe), s.v. αἰτία, ἡ and αἴτιος.

48 See Basil of Caesarea, On the Holy Spirit 4.6; as in Basile de Césarée, Sur le Saint-Esprit. Introduction, texte, traduction et notes (ed. Benoît Pruche; 2nd ed.; SC 17; Paris: Cerf, 1968) 268. In On the Holy Spirit, Basil defends the legitimacy of those doxologies that describe the Spirit proceeding “through” the Son. See esp. Spir. 1.3 (SC 17:256–58); 4.6 (SC 17:268–70); 8.18–19, 21 (SC 17:306–16, 318–20); 16.38 (SC 17:376–84). Concerning the relationship between causality and trinitarian procession, Basil distinguishes between principal, cooperative, and sine qua non causes; Spir. 3.5 (SC 17:264–68).

49 Basil, Spir. 8.21 (SC 17:318–20). Concerning the three persons of the Trinity, Basil names the Father as the principal cause, the Son as the creative (or demiurgic) cause, and the Spirit as the perfecting cause; Spir. 16.38 (SC 17:376–78).

50 Augustine, Trin. 5.5, 6.1–7. See Lewis Ayres, Nicaea and Its Legacy: An Approach to Fourth-Century Trinitarian Theology (Oxford: Oxford University Press, 2004) 376. More broadly, see idem, “The Grammar of Augustine’s Trinitarian Theology,” in Nicaea and Its Legacy, 364–83.

51 Ryder, Career and Writings of Demetrius Kydones, 20. Gregory Palamas was also influenced by De Trinitate: Josef Lössl, “Augustine’s On the Trinity in Gregory Palamas’s One Hundred and Fifty Chapters,” Augustinian Studies 30 (1999) 61–82.

52 PG 152:484a-b. See also PG 152:485ab. Migne provides the following citations for Gregory and Basil: Gregory of Nazianzus, Or. Bas. 33, 36; Basil, Contra Eunom. lib. 1.

53 PG 152:484c–85d.

54 PG 152:481c.

55 Aquinas, ST I^a q. 27, a. 1, co. This is echoed in idem, SCG 4.11.

56 Aquinas, ST I^a q. 28 aa. 1–3.

57 The resulting relations are paternity, filiation, spiration, and procession. For Aquinas, in order for the persons to be really distinct, a real relation must be established. As in the case of causal language, the difference between the inner life of the Godhead and the relationship between God and the world becomes significant. Because God has a logical relationship with creation, this procession ad extra cannot provide the analogical foundation for the distinction of persons. Because the inner processions of knowing and loving are real relations, however, they can provide a basis for the necessary distinctions. Aquinas, ST I^a q. 28 a. 4.

58 Aquinas, ST I^a q. 27, a. 1, co. As in S. Thomae de Aquino Ordinis Praedicatorum Summa Theologiae cura et studio Instituti Studiorum Medievalium Ottaviensis ad textum S. Pii Pp. V iussu confectum recognita (5 vols.;Ottawa: Commissio Piana, 1941) 1:182a.

59 Aquinas, ST I^a q. 27, a. 1, arg. 1, ad 1.

60 Aquinas indicates this transition in the first line of the prologue of question 44: “After considering the divine Persons, it remains to consider the procession of creatures from God”; ST I^a q. 44, prooem (Ottawa ed., 1:279a). See also ST I^a q. 45.

61 In question 44, Aquinas considers creation in relation to God as the cause of being and the mode by which creatures proceed from God as first cause; ST I^a q. 44, prooem.; q. 44, aa. 1–4.

62 Aquinas, q. 44, aa. 1–4.

63 By 1277, these interpretations were condemned, and in the eyes of many Aristotle himself was under general suspicion. See Fernand Van Steenberghen, Thomas Aquinas and Radical Aristotelianism (Washington, DC: Catholic University of America Press, 1980), and idem, Aristotle in the West: The Origins of Latin Aristotelianism (Louvain: Nauwelaerts, 1970).

64 Gilles Emery, Trinity, Church, and the Human Person: Thomistic Essays (trans. Jennifer Harms and John Baptist Ku; Naples, FL: Sapientia Press of Ave Maria University, 2007) 193–96. Dominicans working in Constantinople assisted Aquinas while he was composing his Contra errores Graecorum between 1263 and 1264. Subsequently, when composing his Catena aurea, Aquinas would continue to expand his knowledge of Greek patristic texts. After 1267, Aquinas’s subsequent work would be influenced by Latin translations of Greek works made by William of Moerbeke, a Dominican from the Byzantine missions. Jean-Pierre Torrell, The Person and His Work (trans. Robert Royal; vol. 1 of Saint Thomas Aquinas;Washington, DC: Catholic University of America Press, 1996) 174–76. Pasquale Porro, Thomas Aquinas: A Historical and Philosophical Profile (trans. Joseph G. Trabbic and Roger W. Nutt; Washington, D.C.: Catholic University of America Press, 2016) 176–82.

65 Aquinas, ST I^a q. 33 a. 1 ad 1 (Ottawa ed., 1:214b).

66 Aquinas, Super Sent. I, d. 29, q. 1, a. 1. Gilles Emery, The Trinitarian Theology of Saint Thomas Aquinas (trans. Francesca Aran Murphy; Oxford: Oxford University Press, 2007) 157–58. See also John Baptist Ku, God the Father in the Theology of St. Thomas Aquinas (New York: Lang, 2013) 143–44.

67 For the composition history of the Contra gentiles, see Torrell, The Person and His Work, 332; Porro, Thomas Aquinas, 116–84.

68 Emery, The Trinitarian Theology of Saint Thomas Aquinas, 158. See Aquinas, De pot. q. 10, a. 1, ad 9. De potentia was completed during Aquinas’s Roman period, probably during 1265–1266, the first year of his stay there. Torrell, The Person and His Work, 335.

69 Aquinas, ST I^a q. 33 a. 1 ad 1 (Ottawa ed., 1:214b).

70 Emery, The Trinitarian Theology of Saint Thomas Aquinas, 158.

71 Aquinas, ST I^a q. 36 a. 3 s.c. (Ottawa ed., 1:230a). See Hillary, De Trin. c. 12 (PL 10:471). For a study of the patristic sources for Aquinas, ST I^a q. 36, see Jaroslav Pelikan, “The Doctrine of the Filioque in Thomas Aquinas and Its Patristic Antecedents: An Analysis of Summa Theologiae, Part I, Question 36,” in St. Thomas Aquinas 1274–1974: Commemorative Studies (ed. Étienne Gilson and Armand A. Maurer; Toronto: Pontifical Institute of Mediaeval Studies, 1974) 315–36.

72 Aquinas, ST I^a q. 36 a. 3 co. (Ottawa ed., 1:230a–b). See also ST I^a q. 36 a. 3 ad 4.

73 Aquinas, ST I^a q. 36 a. 3 ad 1 (Ottawa ed., 1:230b).

74 Aquinas, ST I^a q. 36 a. 3 co. Translation mine.

75 Florence, sess. 6. Decrees of the Ecumenical Councils (ed. Tanner), 1:525 ln. 36–42.

76 Ibid., 1:526 ln. 43–527 ln. 10.

77 Ibid., 1:527 ln. 3–10.

78 During these important years leading up to the Council of Florence, both Theodore and Andrew were very active in diplomatic circles. Tsougarakis, The Latin Religious Orders, 205. Loenertz, “Les dominicains byzantins,” 5–61. Even while still in studies, Andrew was called upon to preach twice at the Council of Constance between 1414 and 1417. He was later made archbishop of Rhodes in 1432 and archbishop of Nicosia in 1447. At the Council of Florence, Andrew would be present as an official representative of the Latin Church, where his knowledge of the Greek language and Byzantine theology was highly valued. Tsougarakis, The Latin Religious Orders, 210; Delacroix-Besnier, Les Dominicains, 355–57. Both Chrysoberges would play important roles in the negotiations for union between the Byzantines and Latins in 1415 and 1430, which formed an important precedent for the Council of Florence in 1438–39. See Loenertz, “Les dominicains byzantins,” 5–61. Plested argues that Andrew Chrysoberges, writing on the eve of the Council of Florence, may have been the first to comment explicitly on the incompatibility of Palamite and Thomist doctrines on the essence-energies distinction. Although earlier writers, such as Kydones and Kalekas, would argue against the Palamite doctrine, their reliance on Aquinas in this regard remained unstated. Plested, Orthodox Readings of Aquinas, 119 n. 48.

79 Τόμος ἀγάπης κατὰ Λατίνων (Jassy, 1698), 413–90. See ODCC, s.v. “Dositheus.” See also Meyendorff, “Eglises-soeurs,” 35–46. The version of Kalekas’s De fide that appears in Migne’s Patrologia Graeca—which is cited here—is taken from PG 152:429–662. See n. 4 above. Plested argues that the inclusion of De fide in this volume represents a kind of eventual confirmation of Kalekas’s own intention to compose a Byzantine text aimed at a Byzantine audience: “Kalekas writes as an Orthodox for the Orthodox, but one who recognizes Thomas as an exceptionally useful guide and teacher in the study and exposition of Scripture and the Fathers. Kalekas’ treatise (De fide) is designed to incorporate Aquinas’s wisdom and rigour within a presentation of the teachings of the universal Church. And to a great extent it succeeded: this decidedly Thomist work earned the express approbation of the zealously anti-Latin patriarch of Jerusalem, Dositheos, who published it without attribution in his The Book of Charity Against the Latins. Dositheos commends the work in his introduction as ‘highly theological, highly edificatory, highly clear, and highly Orthodox.’ Rarely has a Byzantine Thomist found such explicit recognition as a standard-bearer for Orthodoxy” (Plested, Orthodox Readings of Aquinas, 117). Plested attributes this quote from Dositheos to the 5th page of the unpaginated preface to the Τόμος Ἀγάπης κατὰ Λατίνων. Loenertz, Correspondance, 22, 200. See also Plested, Orthodox Readings of Aquinas, 117 n. 40.

80 See Martin Grabmann, Mittelalterliches Geistesleben: Abhandlungen zur Geschichte der Scholastik und Mystik (3 vols.; Munich: Huber, 1926–1956) 3:370–410. Jean-Pierre Torrell, Aquinas’s Summa: Background, Structure, and Reception (trans. Benedict M. Guevin; Washington, DC: Catholic University of America Press, 2005) 95–96.