DIODORUS. – Bishop of Tarsus, ascetic and second founder of the Antiochene exegetical school in the first quarter of the 4th century, died before 392. He pursued his studies at Athens (Facundus of Hermiane, Pro defensione trium capit., 4, 2: PL 67, 621 B, II-14), acquiring a broad secular learning, so that the remark of St Jerome attributing to him “ignorantiam saecularium litterarum” (De vir. illustr., 119: PL 23, 750) is not accurate. He was also a disciple of Silvanus, bishop of Tarsus, and of Eusebius of Emesa.
After completing his education, D. devoted himself to asceticism in a monastery near Antioch, where he applied himself to the study of Holy Scripture and became, together with his companion Carterius, superior of a group of ascetics among whom were St John Chrysostom and Theodore of Mopsuestia.
Under the Arian emperors Constantius (337–61) and Valens (364–78), D. and his friend Flavian, not yet priests, carried on untiring activity in defence of the Nicene faith. When Leontius, the Arian bishop of Antioch (cf. Theodoret, Hist. eccl., 2, 19: PG 82, 1060), admitted the Arian Aetius among the deacons, Flavian and D. protested, and Leontius yielded. At the same time D. instructed the people to sing psalms and hymns antiphonally at the gatherings of the orthodox outside the Arian churches. This chant proved so successful that Leontius himself requested that these meetings be held in the churches (Theodoret, ibid.); Semitic sources report that D. had learned this custom during a journey to Persia.
In 361 an orthodox, St Meletius, became bishop of Antioch and ordained the two friends as priests. When Julian the Apostate passed through Antioch the following year, D. was already a priest and known to the emperor as the leader of the Christians. About 372 he went to Armenia, where his bishop Meletius was in exile; there he met St Basil, with whom he formed a close friendship, as appears from Basil’s correspondence (Epist., 135 and 244, 3: PG 33, 572 and 916). After the death of Valens (378), D. was consecrated bishop of Tarsus in Cilicia. He took part in the Council of Antioch the following year and in that of Constantinople in 381 (Theodoret, Hist. eccl., 5, 4: PG 82, 1204 A). In a decree of 30 July 381 Theodosius proclaimed Pelagius of Laodicea and D. of Tarsus as models of orthodox faith for the diocese of the East (Hefele-Leclercq, II, 41). From Jerome’s notice of 392 (De vir. ill., 119) it appears that D. was already dead.
Of D.’s numerous writings (the Suda preserves a list: PG 33, 1553), much has been lost. He commented on almost all the books of the Old and New Testaments. One treatise on hermeneutics survives under the suggestive title: What is the Difference between Theory and Allegory? Polemical-dogmatic treatises were largely directed against the errors of the Jews, pagans, Arians and other heretics. Besides the works listed by the Suda, Photius makes known to us a book against the Manichees and one On the Holy Spirit (Photius, Bibl., cod. 85, 102: PG 103, 288B, 372); Jerome knew a commentary on the Letters of St Paul; and Leontius of Byzantium an anti-Synousiast work, the name being applied to the Apollinarians. For the Syriac lists V. the article by R. Abramowski, Untersuchungen zu D. von Tarsus, in Zeitschr. f. Neutest. Wissenschaft., 30 (1931), pp. 245 ff.
The fragments that have come down to us are found either in exegetical catenae or in polemical florilegia, which makes it difficult to establish their authenticity and to grasp the author’s thought from passages taken out of context.
Migne has collected some fragments on the Octateuch and the Psalms (PG 33, 1561–1628), later augmented in the edition by Deconinck (further additions by R. Devreesse, in Rev. bibl., 45 [1936], pp. 217–20). The hypothesis of Mariès attributing to D. the complete commentary on the Psalms by Anastasius of Nicaea has not been confirmed. The fragments on the Epistle to the Romans have been edited by Staab.
There remain a few dogmatic-polemical passages. Those collected in PG 33, 1560 sqq. are taken either from Leontius of Byzantium (Contra Nestorianos et Eutychianos, III, 43: PG 86, 1, 385 sqq.) or from Cyril of Alexandria (fragments from the work Contra Diodorum et Theodorum: PG 76, 1437 sqq.; some in Mansi, IX, 215 b, 219 b c, 231: Council of Constantinople, III, 553). Other fragments exist in the Palatine Codex of the Council of Ephesus (E. Schwartz, Acta conc. ecc., I, 5, pp. 177–79, before the year 550); Syriac fragments in M. Brière, Fragments syriaques de D. de T. réédités et traduits, in Revue de l’Orient chrétien, 3rd ser., 10 (1946), pp. 231–85. Abramowski has studied the tradition of these fragments in the manuscripts (ibid., pp. 247–53) without addressing the question of their authenticity. M. Richard (Les traités de Cyrille d’Alexandrie...) in his study of the above fragments reaches the following conclusions: D. wrote a two-book work Contra Synousiastas (i.e. against the Apollinarians). Against the first book St Cyril polemicizes in his Contra Diodorum. Six fragments of this first Diodorian book are transmitted in the Palatine Codex (the fourth fragment, homo ungitur Jesus, is from Paul of Samosata); seven or more others may be found in the Philalethos and in the Contra impium grammaticum of Severus of Antioch. Against the second Diodorian book St Cyril likewise polemicized, attributing it to Theodore. When Cyril wrote, he did not have the actual works of D. and Theodore before him but florilegia compiled by Apollinarians (and thus probably also falsified). In this compilation, offered to him in Jerusalem in 438, Cyril would already have found the confusion between D. and Theodore, of which, writing in haste, he was unaware.
There also survives Photius’s long analysis (Bibl., 223: PG 103, 829–77) of the fragments of the Contra fatum, which have been studied by V. Ermoni (Diodore de Tarse et son rôle doctrinal, in Le Muséon, 2 [1901], pp. 424–44) and by P. Doll (Κατά ελαχισμένης, Bonn 1923).
For a stylistic assessment of D., in the absence of complete works, one must rely on the criticism of Photius (Bibl., 223: PG 103, 820 and 877) and of St Basil (Ep. 135: PG 32, 572).