Ranks with Bar-Hebraeus as the most distinguished for scholarship among Syriac writers, 1 born at Ēn-dēbhā in the province of Antioch, probably about A.D. 640. From the trustworthy account of his life by Bar-Hebraeus (Chron. Eccles. i. 289) we learn that he studied first at the famous monastery of Ken-neshrē (on the left bank of the Euphrates, opposite Jerābis) and afterwards at Alexandria, which had of course been for some time in the hands of the Moslems. 2 On his return he was appointed bishop of Edessa by his friend Athanasius II. (of Balad), probably in 684, 3 but held this office only for three or four years, as the clergy withstood his strict enforcement of the Church canons and he was not supported by Julian, the successor of Athanasius in the patriarchate. Accordingly, having in anger publicly burnt a copy of the canons in front of Julians residence, Jacob retired to the monastery of Kaisūm near Samosāta, and from there to the monastery of Eusebhōnā, 4 where for eleven years he taught the Psalms and the reading of the Scriptures in Greek. But towards the close of this period he again encountered opposition, this time from monks who hated the Greeks, and so proceeded to the great convent of Tell Addā or Teleda (? modern Tellādi, N.W. of Aleppo), where he spent nine years in revising and emending the Peshitta version of the Old Testament by the help of the various Greek versions. He was finally recalled to the bishopric of Edessa in 708, but died four months later, on the 5th of June.
In doctrine Jacob was undoubtedly Monophysite. 5 Of the very large number of his works, which are mostly in prose, not many have as yet been published, but much information may be gathered from Assemanis Bibliotheca Orientalis and Wrights Catalogue of Syriac MSS. in the British Museum. (1) Of the Syriac Old Testament Jacob produced what Wright calls a curious eclectic or patchwork text, of which five volumes survive in Europe (Wrights Catalogue 38). It was the last attempt at a revision of the Old Testament in the Monophysite Church. Jacob was also the chief founder of the Syriac Massorah among the Monophysites, which produced such MSS. as the one (Vat. cliii.) described by Wiseman in Horae syriacae, part iii. (2) Jacob was the author both of commentaries and of scholia on the sacred books; of these specimens are given by Assemani and Wright. They were largely quoted by later commentators, who often refer to Jacob as the interpreter of the Scriptures. With the commentaries may be mentioned his Hexahemeron, or treatise on the six days of creation, MSS. of which exist at Leiden and at Lyons. It was his latest work, and being left incomplete was finished by his friend George the bishop of the Arabs. Among apocrypha, the History of the Rechabites composed by Zosimus was translated from Greek into Syriac by Jacob (Wrights Catalogue 1128, and Nau in Revue sémitique vi. 263, vii. 54, 136). (3) Mention has been made above of Jacobs zeal on behalf of ecclesiastical canons. In his letter to the priest Addai we possess a collection of canons from his pen, given in the form of answers to Addais questions. These were edited by Lagarde in Reliquiae juris eccl. syriace, pp. 117 sqq. and Lamy in Dissert. pp. 98 sqq. Additional canons were given in Wrights Notulae syriacae. The whole have been translated and expounded by Kayser, Die Canones Jacobs von Edessa (Leipzig, 1886). (4) Jacob made many contributions to Syriac liturgy, both original and translated (Wright, Short Hist. p. 145 seq.). (5) To philosophical literature his chief original contribution was his Enchiridion, a tract on philosophical terms (Wrights Catalogue 984). The translations of works of Aristotle which have been attributed to him are probably by other hands (Wright, Short Hist. p. 149; Duval, Littérature syriaque, pp. 255, 258). The treatise De causa omnium causarum, which was the work of a bishop of Edessa, was formerly attributed to Jacob; but the publication of the whole by Kayser 6 has made it clear that the treatise is of much later date. (6) An important historical work by Jacoba Chronicle in continuation of that of Eusebiushas unfortunately perished all except a few leaves. Of these a full account is given in Wrights Catalogue 1062. (7) Jacobs fame among his countrymen rests most of all on his labours as a grammarian. In his letter to George, bishop of Sĕrūgh, on Syriac orthography (published by Phillips in London 1869, and by Martin in Paris the same year) he sets forth the importance of fidelity by scribes in the copying of minutiæ of spelling. In his grammar 7 (of which only some fragments remain), while expressing his sense of the disadvantage under which Syriac labours through its alphabet containing only consonants, he declined to introduce a general system of vowel-signs, lest the change should contribute to the neglect and loss of the older books written without vowels. At the same time he invented, by adaptation of the Greek vowels, such a system of signs as might serve for purposes of grammatical exposition, and elaborated the rules by which certain consonants serve to indicate vowels. He also systematized and extended the use of diacritical points. It is still a moot question how far Jacob is to be regarded as the author of the five vowel-signs derived from Greek which soon after came into use among the Jacobites. 8 In any case he made the most important contribution to Syriac grammar down to the time of Bar-Hebraeus. (8) As a translator Jacobs greatest achievement was his Syriac version of the Homiliae cathedrales of Severus, the monophysite patriarch of Antioch (512518, 535536). This important collection is now in part known to us by E. W. Brookss edition and translation of the 6th book of selected epistles of Severus, according to another Syriac version made by Athanasius of Nisibis in 669. (9) A large number of letters by Jacob to various correspondents have been found in various MSS. Besides those on the canon law to Addai, and on grammar to George of Sĕrūgh referred to above, there are others dealing with doctrine, liturgy, &c. A few are in verse.
Jacob impresses the modern reader mainly as an educator of his countrymen, and particularly of the clergy. His writings lack the fervid rhetoric and graceful style of such authors as Isaac of Antioch, Jacob of Sĕrūgh and Philoxenus of Mabbōg. But judged by the standard of his time he shows the qualities of a truly scientific theologian and scholar.