A Compendium on the Soul · Avicenna
SECTION FIRST
We now start by saying that not a shadow of doubt or perplexity hampers the mind, as to things, that some of them share some one thing in common, and differ in an other; and that that which is shared in common is other than that in which they differ. The mind encounters all bodies whatsoever as having this in common, viz. that they are bodies; and afterwards it encounters them as differing in that they move (in different ways); otherwise there would be no such thing as rest of a body, and not even such a thing as motion of a body, except along a circle, seeing that of motion in a straight line it is established by its very form that it will not proceed save from stoppings and to stoppings (resting-places to resting-places). Hence it is evident that bodies are not to be clothed with the attribute of motion because they are bodies, but for reasons (causes) above and beyond their corporeity, from which causes their motions proceed, like the resulting of the footprint from the walker (or, just as the effect proceeds from the agent).
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.
Text from Project Gutenberg, public domain in the United States.