the later philosophers call the Necessary Existent in itself. This is the method of the early Peripatetics.

As for the method well known among the later philosophers—inferring the Necessary Existent from existence as such—this is the method followed by Ibn Sīnā and his followers.

Now, the substance of this method of Aristotle and his Peripatetic followers is that every body subsists only through its nature; its nature subsists only through volitional motion; and that motion subsists only through an unmoving object of love and desire. Aristotle then raised an objection to his own argument: one can suppose that the body’s particular nature and its motion cease to exist when it dissolves into something simpler than itself. The mover would then be the cause not of its essence, but only of its composition.

He answered that the simple exists only in the mind, not in external reality. His followers offered a second answer: that which it dissolves into possesses receptivity, and receptivity is motion.

This answer is untenable. Even if we suppose that it possesses receptivity, this need not be volitional motion arising from desire. If the motion is not volitional and does not arise from desire, it does not entail the existence of an object of love; rather, it entails the existence of an originating agent. They, however, have not established that.

Aristotle’s supposition is likewise unsound. He supposes that motion can occur only through a nature that entails volitional motion. Although this supposition is itself open to discussion, this is not the place to elaborate on it. Yet even if it is granted to him, all it establishes is that the body moving by volition depends upon the object of desire that is its end, and that it cannot exist without it. Thus, the existence of that object is a condition for the body’s existence. This may be expressed as follows: a body cannot subsist except through its nature; its nature cannot subsist except through its motion; and its motion cannot subsist except