SUB-SECTION D:--Among the proofs that guide (point) to the validity of this contention is what I am now going to say.
No doubt a live body and live organs or instruments, if they accomplish their growing age and the age of standstill, begin to wither and diminish, to lose power and waste away, which [in human beings] is on passing forty years. Now, were the rational reasoning power a corporeal organic power, then there would be found not one single individual of mankind at these years of his age but what this power of his would have begun to diminish. But the case in most people is quite otherwise, nay indeed it is usual amongst the majority that as to intellectual power they improve in cleverness and increase in insight. Hence the structure of the rational power is not upheld by the body nor by the organ; and hence this power is an essence standing of itself, which is what we wished to show.
SUB-SECTION E:--Among the proofs for the validity of this contention is the following also.
So much at least is clear, namely that not one of the bodily powers has the strength for performing infinite multifarious actions; and this is so because the strength of the one half of such a body will inevitably be found to be weaker than the strength of the whole; and the weaker is less powerful to perform and overcome than the stronger; and whatsoever, other than the infinite, gets less is itself finite; hence the strength of each one of the two halves is finite; hence too their sum is finite, since that the sum of two finites is itself finite, whereas it has been contended that it is infinite, which is a contradiction. Hence the sound view is that the powers of bodies are not powerful enough to perform infinite manifold deeds. The rational power however is powerful enough to perform many infinite deeds, seeing that forms geometrical, arithmetical, and philosophical, which the rational power has to perform among other of its acts, are infinite. Therefore the rational power is not standing by and through the body, and hence therefore it stands of itself and is an essence of itself.
Further, so much at least is clear that the corruption of one of two conjoined essences does not entail and enjoin the corruption of the other: wherefore the death of the body does not render obligatory the death of the soul, which is what we wanted to show.