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© 1998 Jeffrey Macdonald; all rights reserved.
The Dialogue with Paul of Nisibis is a transcript of a debate which occurred between theological delegations headed by Justinian and Paul of Nisibis concerning whether Christ had one or two hypostases/qnome, which is partially preserved in a Syriac manuscript connected with the Monothelites.  The occurrence of the debate is attested to in several independent sources, the most important of which is the Nestorian History:
It is said that after the conclusion of the peace with Khosroes, Justinian asked him to send him some wise Persians. Khosroes sent him Paul the Metropolitan of Nisibis, Mari Bp. of Belad, Bar-Sauma Bp. of Qardou, Isaiah a teacher in Seleucia, Iso-yahb of Arzoun who became Catholicos of the Church of the East, and Babai Bp. of Sinjar. [Justinian] honored them all. The Debate, which was recorded, lasted three days. They made known the Orthodox Faith. [Justinian] said to Babai, "I wish that you tell me some of the passages from the Scriptures and the commentaries of the Fathers which you allege." [Babai] cited many passages which the soul of the Emperor was inclined to receive. They made him to understand that neither the nature is able to exist without the hypostasis nor the hypostasis without the nature, and that by consequence the two natures are not able to be a single hypostasis. [Justinian] heard them, and they returned filled with honor. Justinian changed afterwards when he anathematized Diodore and his companions. 
The descriptions of the debate in these sources are consistent with the contents of the existing Dialogue.
The Nestorian History dates the debate to after a peace between Justinian and Khosroes. These rulers concluded two major peace treaties in 532 and 561 with two five year truces being made following the Persian invasion in 540.  A. Scher and Arthur Voobus identify the debate with the first treaty and Justinian's colloquy with the Monophysites in 532, but for this reason are forced to conclude that the references to Paul of Nisibis attending as a bishop are anachronisms because he was consecrated after 551.  In support of an early date for the debate, the Nestorian History ascribes Justinian's condemnation of Diodore and his companions to after the debate, which would imply a date prior to 543. In contrast, A. Guillamont has argued that the Nestorian History is placing the debate after the peace of 561.
The doctrinal positions ascribed to Justinian in the Dialogue are largely consistent with those found in his other writings and can be derived from those writings with only a few exceptions. The portions ascribed to Justinian also have affinities with the writings of Leontius of Jerusalem, which would be consistent with Justinian's other works.  The similarities between Leontius of Jerusalem's Against the Nestorians and the Dialogue with Paul of Nisibis may also result from Leontius of Jerusalem using the debate as a basis for portions of Against the Nestorians. This is suggested by the similarity between the Nestorian portions of the Dialogue with Paul of Nisibis and those of book two of Leontius of Jerusalem's Against the Nestorians.
While the Orthodox portions of the Dialogue could be expected to have derived from Leontius of Jerusalem's influence, the Nestorian portions in a debate could not. The dependence of Against the Nestorians on the debate underlying the Dialogue with Paul of Nisibis is further suggested by the topic following the shared material in both documents being the Orthodox charge that two hypostases in Christ would lead to two Sons. Acceptance of this relationship would require that the debate occurred in 532 rather than 561 as Against the Nestorians was written about 544.
The doctrinal positions ascribed to Paul of Nisibis are consistent with descriptions of his position and with the later position of the Persian Church.  The positions of the opponents in the Dialogue reflect different conceptions of the word hypostasis/qnoma. These conceptions are consistent with the linguistic backgrounds of the two sides, Greek and Syriac. 
A difficulty with accepting Justinian's authorship of the Dialogue with Paul of Nisibis is its support for one personal activity in Christ. This would seem to contradict the support of two natural activities in Christ defended in the fragment of the Epistle to Zoilus. However, Justinian's Chalcedonian contemporaries, Ephrem of Antioch and Leontius of Jerusalem differentiated between natural and personal properties and activities in order to preserve both the fullness of each nature and the unity of subject in Christ. Since Justinian's works have affinities with both of these authors it seems likely that Justinian would also have supported both types of activities in Christ. The fragment is thus important as a source for understanding part of the neo-Chalcedonian background to the Monoenergist controversy of the seventh century. 
Have mercy, O Lord, upon Thy servant the translator Jeffrey, and on Caryn, Alexander, and Anna.