The inscription in the title of the Kitab al-Istidlal? “Book of Dialectic, written by ‘Abd al-Mash al-Isra‘li al-Raqqi, who became a Christian at Misr thanks to ‘ala yadd Shaykh Mansur ibn Sahlan the physician” (Vatican Library, Arabic manuscript 145, fol. 114b)? reveals that ‘Abd al-Masih was a Jew from Raqqah in Syria who was converted to Christianity in Egypt, probably before 969, the year Cairo was founded.

Vatican Library, Arabic manuscript 145, fol. 114b
Vatican Library, Arabic manuscript 145, fol. 114b

The physician who converted him was the famous Abu al-Fath MANSUR IBN SAHLAN IBN MUQASHSHIR, who practiced his art for many decades at the court of the Fatimid caliphs in Cairo, especially under al-‘Aziz (975-996) and al- Bi-Amr Allah (996-1021).

The Book of Dialectic, and especially its third and fifth sections, shows that ‘Abd al-Masih was well versed not only in philosophy but also in mathematics.

Six treatises, contained in two manuscripts, have been attributed to ‘Abd al-Masih. One of the is in the Vatican Library (Arabic manuscript 145, copied in Egypt at the end of the thirteenth century); the other belonged to the heirs of Karkur Sa‘igh, members of the Armenian community of in the 1920s. It was described by Paul Sbath in his catalog. Unfortunately, this manuscript no longer exists.

In fact, the three treatises in the Vatican manuscript are not works of ‘Abd al-Masih. The works ascribed to him follow:
1. The Treatise on the Rational was attributed to ‘Abd al-Masih by Joseph ASSEMANI in his of the Vatican manuscript 145, fol. 1a-28a and in Sbath’s description of the manuscript (1938, p. 53, no. 410), which was repeated by Steinschneider (1877, p. 115). This treatise was actually the work of AWLAD AL-ASSAL (as shown by Graf, 1947, pp. 403f).
2. The Brief Treatise on the Trinity was also ascribed to ‘Abd al-Masih by Assemani (1831, p. 271, col. 2), an observation followed by Steinschneider (p. 115). But it is in fact by al-SAFI IBN AL-‘ASSAL (see Graf, 1947, p. 395, no. 4).
3. The Proof of the Coming of Christ was included in the manuscript (Sbath, 1938, p. 53, no. 409), which most probably constitutes the first part of The Book of Dialectic (see below).
4. The was also part of the manuscript (Sbath, 1938, p. 53, no. 411).
5. The Triumph of the Cross over Judaism and Paganism is included in the manuscript (Sbath, 1938, p. 53, no. 412).
6. For the now lost Book of Dialectic, the Vatican manuscript 145 has preserved a compendium (mukhtasar) with fol. 114b-22b (original Coptic numbering: 121b-29b). Any analysis of the work must be based on this compendium.

The Kitab al-Istidlal consists of an introduction and five parts. The introduction repeats the eight traditional kephalaia (headings) employed by the Alexandrian commentators on the works of Aristotle. These were used repeatedly throughout traditional Arab philosophy (by al-Farabi, Yahya ibn ‘Adi, ‘Abdallah ibn al-Tayyib, etc.). But only six of the eight kephalaia are found here: goal, usefulness, place, author, method, and divisions.

The first part deals with proofs concerning the coming of Christ, starting with prophecies in the Old Testament. The compiler of this material (probably Al-Safi ibn al-‘Assal) did not summarize this segment. Instead, he indicated that sufficient information of this sort appeared in the two books of al-Kashkari and al-Ruhawi, doubtless works by the priest Israel al-Kashkar (Graf, 1947, pp. 155f.) and Taddawus al-Ruhawi, author of The Book of the Master and of the Disciple (Graf, 1947, p. 219, par. 1-2; p. 473, no. 9). These two books are mentioned by Abu al-Barakat Ibn Kabar (d. 1324) in Chapter 7 of his Misbah al-Zulmah, in a discussion of authors (cf. Khalil Samir’s edition, pp. 302-303, nos. 9- 70).

The second part details the ways in which is said to be substance by the Christians.

The third part is the best developed. The author explains the meaning of the Christian Trinity in seven different ways: by analogy with man ( is living, knowing, powerful); by analogy with geometry (the body is reality which is perfect, unified, and threedimensional); by analogy with mathematics (the number three is the most perfect because it contains both an odd and an even number); by analogy with logic (gender, species, and individuality); through the testimony of the prophets in the Old Testament; through philosophy (the primary cause, the intellect, and the are the only three realities that are neither attainable through reason nor through the senses; they are the images of the Father, the Son, and the Holy Ghost; likewise, the Sabaeans venerate three altars, which are the world of the primary cause, the intellect, and the soul); and through the Gospel, because Christ and the Apostles are true. He then answers two objections: “Why limit oneself to only three hypostases?” and “If the eternal one joins the created, He becomes himself created.”

The fourth part focuses on the Incarnation, employing two approaches: through prophecies of the Old Testament and through miracles. The compiler’s summary does not do justice to this piece.

The fifth part responds to the question of why Christ did not prevent the Jews from killing him. If He was incapable, it means He was not God, and if He was capable and did not do so, then the Jews are not guilty. ‘Abdal-Masih’s answer rests on three premises: that God, in creating man, did so for man’s own good; that created men free and not constrained, an argument that sets predestination against divine foresight); and that though God sent prophets to one specific people, prophecy proved futile; He then became incarnate in order that all humanity might reach perfection. (Here is inserted a marginal gloss that should probably be attributed to Al-Safi ibn al-

He then offers two answers to the question of why Christ did not prevent His own death. If He had, He would not have acted fully as a man and would therefore not have served as an example for the human race. And if He had forced the Jews not to kill Him, he would have been limiting their free will, the very quality that makes
them human.

The treatise ends with a beautiful prayer in rhymed prose.


  • Assemani, J. S. Scriptorum veterum nova collectio e vaticanis codicibus edita, Vol. 4, pt. 1, pp. 271-72, ed. Angelo Mai. Rome, 1831. of Vatican Library, Arabic manuscript 145.
  • Sbath, P. Al-Fihris. Catalogue de manuscrits arabes, Vol. 1, p. 53, nos. 409-412. Cairo, 1938.
  • Steinschneider, M. Polemische und apologetische Literatur in arabischer Sprache, pp. 115-16, no. 91. Leipzig, 1877; reprint, Hildesheim, 1966.
  • Die arabische Literatur der Juden. Ein Beitrag zur Literaturgeschichte der Araber grossenteils aus handschriftlichen Quellen. Frankfurt, 1902; reprint, Hildesheim, 1964.