So much having become clear to us, we say that we find, among bodies generated from the Four Elements,[7] such as moves, not by constraint, in two kinds of motion between which there is more or less difference: The one kind inherent in its element by reason of the supremacy over it of the power of one of its constituents, and thus decreeing its motion towards the position in space naturally appointed for it, as for example a man’s moving by the nature of the preponderating[8] heavy element in his body downwards; nor will this kind of the motions of bodies be found to take place save in one direction and with a constant tendency; The second kind of motion going against the decree of its element, which decree is either rest in the natural position as soon as it reaches that position, as for example a man’s moving his body along its natural home which is the Earth’s surface; or else a moving away from the natural position when already separated from it, like a flying bird’s motion with its heavy body high up through the sky. It has thus been made manifest [to the reader] that the two motions have two accounting causes, and that they are quite different one from the other: the one is called Natural, and the second called Soul or Spiritual Faculty. Hence it is quite sound, as to motion, to affirm the existence of spiritual faculties.
Whereas, in respect of Perception, because that bodies exist with this in common, viz. that they are bodies, and with this in distinction, viz. that they are repeatedly perceptive, it is quite manifest by the first (preceding) process of discrimination that perception will not ever differ from bodies through difference of their substance, but by certain powers or faculties borne within those bodies. It therefore becomes quite clear by this sort of exposition that spiritual faculties have an existence: and this is what we wished to demonstrate.
[6] Reality of existence; or its whereabouts. Doctor S. Landauer thinks that the word ayniyyat in the text must be wrong, because nowhere throughout this section is the «Whereabout» of the mental powers so much as hinted at; whereas the burden of the whole chapter is to prove merely that such powers do exist, i.e., their inniyyat, which is a word used by Arab Logicians.