Aquinas and Classical Islamic Philosophy on the Divine

Aquinas and Islam

Thomas Aquinas offered the classic medieval Christian summation of belief in God, and more particularly offered the "five ways" to prove the existence of God. There are, of course, substantial overlaps between Aquinas and classical Islamic philosophy and theology: Aquinas was compelled to read and take seriously Averroes, for a start. But there is also the common inheritance of classical Greece -- Aquinas has in common with the classical Islamic philosophers a reliance on Aristotle's writings as a basic rational and scientific view of the world. Indeed the purpose of Aquinas' Summa Theologica was to reach a harmonious synthesis between Aristotle's scientific worldview and the Christian theology that had been expounded by the early Church fathers. I propose to examine two of Aquinas' five arguments in closer detail, and to examine how they relate to classical Islamic theology and philosophy.

The first of Aquinas's arguments that I'd like to examine is the "argument from motion," also known as the prime mover argument. It is worth noting at the outset that this is the one which bears the most substantial relation to classical Islamic philosophy, because it is the one that adheres most closely to the common source between Aquinas and the Islamic philosophers, which is Aristotle. In some sense Aquinas's argument hinges quite clearly on Aristotle's rationalistic and scientific worldview: it begins with the notion, familiar from physics, that the universe is full of bodies in motion. This includes the objects in the heavens -- planets and stars can be observed to move -- as well as objects on earth. An arrow shot from a bow is propelled with motion, until that motion ceases when the arrow hits something or runs out of force and falls to the ground. The fact of motion is evident to human senses: Aquinas is beginning with this basic empirical observation. However Aquinas distinguishes the physical facts of the world into actuality and potentiality. An arrow still in the quiver has potential: but the arrow in flight has actuality. In other words, the object in motion has been moved by something else -- the arrow only takes flight because we have moved it.

Aquinas sees the concept of motion more largely than mere physics, however: in this case, a sunflower seed also has potential, and its growth into a sunflower is a form of motion. If ever motion has some cause, then it is logical to go back and find what has set that potential into motion. The case of the arrow is obvious: it requires an archer to shoot it. The case of the sunflower seed seems similarly obvious: it came from a previous sunflower plant. In all of these cases, though, Aquinas suggests that the chain of dependent states requires a beginning somewhere: there must have been a Prime Mover to set all of this into motion, or otherwise there would be no such motion. The important thing to note is that, of course, there could be such a thing as an infinite chain of causality, which is why Aquinas is careful not to couch the argument in terms of causality but rather in terms of potentiality and actuality, which is necessarily hierarchical. It is through this hierarchy (rather than through the mere chain of causality) that Aquinas is able to posit that the Prime Mover must logically exist, and this Prime Mover must be God. The objections to the argument are pretty easily stated. In suggesting that it is a law everything which moves has been moved by something else, Aquinas is left with a God that somehow violates the law. If God somehow has a privileged definition already and is permitted to violate the first premise of the argument, then the reasoning here is basically circular. It is also possible to question Aquinas' ideas of actuality and potentiality: this implies that of necessity all processes are teleological and have a beginning and end. This seems to be accepted by Aquinas without offering any proof. Likewise the argument does not seem to deal with the notion of an infinite and eternal universe of objects already in motion -- this would seem to be about as logical a conclusion to draw as the existence of a Prime Mover.

The way in which this argument is employed differently in classical Islamic philosophy is actually quite interesting. We might compare Aquinas' argument here with Avicenna's use of Al-Farabi's concept of the "active intellect." Aquinas' prime mover argument is fundamentally Aristotelian, and thus Avicenna and al-Farabi were both familiar with the Aristotelean notion that God as Prime Mover could be logically deduced from the motion of planets and stars. For Avicenna, however, the notion of "active intellect" (borrowed from al-Farabi but here repurposed) is understood as the necessary manifestation of God in the world: the movements of things from potentiality to actuality is an intellectual movement (as well as a physical) and the form and shape that appears in matter is actually -- in Avicenna's philosophy -- an emanation from God's active intellect. As Leaman puts it, "this is not a matter of choice or God's grace but rather a necessary implication of the active intellect's essence" (Leaman 113).