The Aquinas Institute is pleased to announce the publication of St. Thomas’s commentary on Aristotle’s Metaphysics in a new Latin-English edition, with the text of Aristotle in Latin, Greek, and English. Volume I and Volume II can be purchased through the St. Paul Center website.
Following his master Aristotle, St. Thomas taught that metaphysics is the supreme human science, the science that directs all other sciences, the science that rightly lays claim to the name “wisdom”. Any disciple of St. Thomas should be eager to learn metaphysics, and one might suppose this means learning metaphysics the way St. Thomas did, namely from Aristotle.
But there is a catch. Avicenna, one of the most brilliant of medieval Arabic commentators on Aristotle, described his early experience with the Metaphysics:
I read the Metaphysics [of Aristotle], but I could not comprehend its contents, and its author’s object remained obscure to me, even when I had gone back and read it forty times and had got to the point where I had memorized it. In spite of this I could not understand it nor its object, and I despaired of myself and said, “This is a book which there is no way of understanding.” 
Any reader of Aristotle could make Avicenna’s words his own. Clearly, commentary is needed.
Aquinas’s own commentary, of course, best shows how St. Thomas himself approached the text of Aristotle. Recognized as “intelligent and profound,” St. Thomas’s commentary does not always stop short at what Aristotle said but presses on to what, in St. Thomas’s mind, Aristotle was really aiming at.  In other words, St. Thomas is interested not just in Aristotle’s text but in the realities themselves that Aristotle meant to address. His commentary is ideal for those who wish to be, not just historians of metaphysics, but metaphysicians. 
The Latin text used in this Aquinas Institute volume is the 1964 Marietti edition, the work of M. R. Cathala, OP, and Raymund M. Spiazzi, OP, with some minor reformatting to align with Aquinas Institute conventions. 
The English translation is based on the work of John P. Rowan, originally published by the Henry Regnery Company in 1961. The Aquinas Institute has edited the translation extensively, retranslating segments and supplying parts that were missing in Rowan’s text.
The text of Aristotle requires more explanation. St. Thomas sought the best texts available to him, and he seems to have worked with at least five different Latin translations of the Metaphysics.  In this Aquinas Institute volume, the Latin text of Aristotle is simply what one finds in the Marietti edition, untouched. However, the English text of Aristotle has been rendered to match closely the wording St. Thomas seemed to have before him for a given phrase.
Then there is the Greek text. It might seem odd to include the Greek text, since St. Thomas did not read Aristotle in Greek, but the Aquinas Institute approaches St. Thomas much as St. Thomas approached Aristotle: the reader should be interested not only in St. Thomas’s text, considered as a historically bound and hence partially outdated attempt, but also and chiefly in the truth of things. It may be that the Greek text will shed new light on an obscurity in the Latin translations that confounded St. Thomas; it may reveal St. Thomas’s remarkable ability to penetrate past the deficiencies of the translations; it may even open up a metaphysical insight that St. Thomas did not discern in the text. For all these reasons, the Greek text of Aristotle is taken from the best edition currently available, namely that of W. D. Ross (Oxford, 1970). Certain important emendations were found necessary, but Ross’s text is presented here largely untouched.
The sweep of Aristotle’s text is tremendous. He begins with a history of metaphysics prior to his work and then, over several books, defines the discipline and methods of metaphysics. He goes on to examine the fundamental principles of being, including substance, potency and act, and the difference between material and immaterial substances. Finally, in the closing book, Aristotle argues that, as St. Thomas puts it in the final sentence of his commentary:
there is one ruler of the whole universe, the first mover, and one first intelligible object, and one first good, whom above he called God, who is blessed for ever and ever. Amen.
 William E. Gohlam (ed.). The Life of Ibn Sina, Albany, State of New York University Press, 1974, pp. 33-35, cited on Wikipedia.
 Jean-Pierre Torrell, OP, Saint Thomas Aquinas: The Person and His Work, vol. 1 (trans. Robert Royal; Washington, D.C.: The Catholic University of America Press, 1996), 237-239.
 One historical shortcoming is worth noting: although St. Thomas was aware of the existence of books 13 and 14 of the Metaphysics, he does not comment on them directly.
 As yet, no one has completed a critical edition of the text of Aquinas’s commentary.
 Torrell, Saint Thomas Aquinas, 232.