When Islam entered the sophisticated world of the Byzantine empire, the works of Plato and of Aristotle were made available to them by virtue of Syriac translators from Greek into Arabic (Richard Walzer , Greek into Arabic: Essays in Islamic Philosophy (Columbia: University of South Carolina Press, 1962). Of the works of Plato, it was the Republic that offered a model for the role of reason in the formation of a new society, and al-Farabi (875–950) articulated that model in his ground-breaking essay on the “ideas of the inhabitants of the virtuous city” (Richard Walzer , Al-Farabi on the Perfect State (Oxford: Clarendon Press, 1985). A distinctively Islamic note was struck by insisting that those responsible be prophets, as well as philosophers, since the earthly imitation of divine ordering needs to be communicated to each person in society, few of whom can follow the pattern of deductive reasoning that comprises the original emanation. It is the Qur’an, after all, which offers the paradigm of a text divinely revealed and hence impeccably wise, yet cast in a language accessible to all, replete with images and examples. None but prophets are able to order metaphor and image so as to communicate the results of philosophical reasoning, so Muhammad offers the paradigm for a responsible and wise ruler. It was Aristotle’s Metaphysics , however, which offered the paradigm for doing philosophy to al-Farabi’s successor, Avicenna (980–1037). His al-Shifa adapted the cosmological scheme of al-Farabi, whereby the planetary spheres transmit the primary causal infl uence of the One successively to the earth (Avicenna , The Metaphysics of Healing , trans. Michael Marmura (Provo, Utah: Brigham Young University Press, 2005) ; Robert Wisnovsky , Avicenna’s Metaphysics in Context (London: Duckworth, 2003). What Avicenna added to al-Farabi was an all-important distinction between this ordering and the activity that suffused it.

The Distinction of Essence from Existing

God alone, as both al-Farabi and Avicenna had averred, is understood to be One whose very nature is to exist; everything else must have existence bestowed upon it by the One to whom everything that is traces its origination. In this way the distinction of essence from existence offered Avicenna a handy way of articulating what he had already recognized to be the fundamental division in being: between that One, which exists of itself, and everything else, which may or may not exist. Aristotle had defi ned contingency in terms of some things being able to be other than they are; Avicenna found a yet deeper understanding: everything other than the One source of all might never have been at all! By focusing in this fashion on existing as something that “comes to” an essence, he was able in one formula to distinguish necessary from contingent beings, as well as to limit necessary being to the One, so offering a philosophical analogue to the Qur’an’s insistence that all-that-is derives from a single creator. Furthermore, the formula that God is that very one whose essence is to exist provides a formulation of “necessary being,” which corresponds to the deeper understanding of contingency just noted. It is this formulation that Aquinas will exploit to offer a way of uniquely characterizing God, as well as signaling “the distinction” of creatures from the creator (ST I q.3 a.4: “God is God’s own existing”).

Moses Maimonides

Moses Maimonides (1135–1204) lived all of his life in the Islamicate, that is the linguistic and cultural world of Islam, coming eventually to serve as court physician for Saladin in Foster, the modern Cairo. He composed works of philosophy in Judaeo-Arabic (that is, Arabic with Hebrew orthography), the most signifi cant of which is the Guide of the Perplexed , addressed to his student, Joseph. It was quickly translated into Hebrew, coming to Aquinas’s attention in Latin translation. Aquinas’s citations of this work show that he sensed an affi nity with “Rabbi Moses,” engaging his work in a spirit of shared inquiry, notably around the issue of free creation and that of “naming God,” another place where revelation and reason intersect. As for creation, medieval discussions tended to focus on the eternity of the world versus its beginning in time, refl ecting a religious concern that divided Jewish, Christian, and Muslim thinkers sharply from their pagan predecessors. Aristotle had maintained the eternity of the world because he had no way of conceiving it as a whole but could only presume it as a given—as the context for whatever else might be said or thought. Aquinas will accept Maimonides’ contention that we cannot demonstrate from such a purposeful dependence clearly “in favor of the world’s having been produced in time” (Ibid. 2.21), yet the presumption in favor of an eternal world had also been shown to be undemonstrable, leaving Torah believers free to accept creation de novo , as well as ex nihilo.

• Avicenna, Aquinas, and Maimonides grappled with reconciling creation with pre-existent matter in philosophical terms
• Avicenna focused on reconciling Qur’anic beliefs with eternal matter, while Aquinas distinguished between real possibility and conceptual non-repugnance
• Maimonides emphasized practical knowing to understand divine knowing
• Aquinas refined Avicenna’s ideas and identified existence as the primary effect of the first cause
• Aquinas emphasized that existence is fundamental to things and specified what comes forth from God