Whether the heat, which is an instrument of the soul, is an elemental heat.
Further one inquires whether the heat, which is an instrument of the soul, proceeds from the elements or is an elemental heat.
1. And it seems not. For it is proper to an elemental heat to consume and destroy. But it is proper to a celestial heat to preserve, and the same is true for a natural heat. Since then the heat, which the soul employs, conserves life and does not corrupt it, this heat is a celestial and not elemental heat.
2. In addition, whatever appears in posterior things flows in from the prior things. But the heat that is in animals is the principle of life. Therefore, it flows in from prior causes of life. But the prior causes of life are either the soul or the celestial
To the contrary. Whatever is in a mixed body comes to it from mixables. But this heat is the heat of a mixed body. Therefore, it proceeds from mixables.
To this one must respond that the heat that the soul employs comes to it from mixables, but in some cases it is assigned to a celestial heat. This can be explained from the effects of this heat. For an elemental heat acts on an object and on its own proper subject; thus heat acts on wood, and also consumes other things which it touches by means of its own subject. And the heat that the soul employs acts on an object in the same way, as is clear in the digestion of the nutriment. And it also acts on its subject, since when the nutriment is absent this heat cannot cease from acting, and this is why it then acts on the radical moisture, which is its proper subject. Therefore, in this respect this heat resembles an elemental heat. Yet since this heat is also the principle of life, in this respect it resembles the celestial heat, whose function is to conserve other things. Thus this heat is partly analogous to an elemental heat, and partly analogous to a celestial heat, but it nevertheless differs in number from each of these, because when the elemental heat arrives, this heat departs, and when this heat arrives, the elemental heat departs. And in the same way the celestial heat acts on it and consumes it. And this is why one must say that each is analogous to the other but, nevertheless, also distinct from the other.
1. On to the arguments. To the first, one must respond that although this heat conserves life, it is nevertheless not a celestial heat although it is analogous to it in this respect.
2. To the second argument one must reply that all these bodies below receive the influence of bodies above. Thus this heat receives influences both from the soul and from bodies above, because this heat appears as a result of the commixture of mixables but is governed by the soul's power. And an indication of this is that when the soul departs [the body] at death, the power of this heat changes.
One must respond to the argument to the contrary that this heat appears from mixables, yet it is nevertheless governed during its operation by the soul's power, and it differs, then, from an elemental heat.
Whether spirit is necessary in animals.
One inquires further concerning spirit. And first, whether spirit is necessary in animals.
1. And it seems not. For in every mixed body, heavy things are dominant. Therefore, since spirit appears from a commixture, the heavy dominates in the spirit. But heavy things are dark, and dark and heavy things are really not well suited for the motion and cognitive function of animals. But spirit is not established for any other purpose. Therefore, it is superfluous and unnecessary.
2. In addition, spirit is established for the union of the soul and the body. But just as there is a difference between body and soul, so there is a difference between spirit and soul. Therefore, there must be some other medium to unite spirit and soul, and so on to infinity. But it is not proper to proceed to infinity, as the Philosopher proves elsewhere. Therefore, it is not proper to place spirit as a medium between body and soul as a unifying medium, just as the Philosopher implies.
3. In addition, principles are simpler than things that take their origin from principles. But spirit is not required as a medium between the form of an element and its matter, and therefore neither is the spirit required as a medium between the soul and the body. For if it were, then spirit, which is derived from a principle, would be subtler than its principle because no form of an element can act as a medium.
The Philosopher implies the opposite in the text.
One must respond that spirit is necessary for animals. And the reason for this is that every bodily operation occurs through a corporeal medium. But motion and sense cognition are bodily operations. Therefore, of necessity they occur through corporeal media. But the principles of motion and sensation come from determinate parts. Therefore, it is necessary to posit some medium through which sense and motion flow to the other parts. But spirit is this medium.
Moreover, the sensitive power adds over and above to the vegetative power, just as, as Aristotle indicates in the second book of On the Soul, a four-sided figure adds to a three-sided one. Therefore, the instrument through which the sensitive power operates adds to the medium through which the vegetative power operates, and this in the realm of spirit [in spiritualitate] since the sensitive power is more spiritual. But the vegetative power operates with a mediating heat. Therefore, it is necessary to posit something more spiritual through which the sensitive power operates. And this is nothing other than spirit. Thus it is necessary to posit spirit, because the motive power and, similarly, the sensitive power, are principally rooted in determinate parts, and yet these are moreover suited for other parts as well. This would not be the case if the influence of the principals did not occur in posterior ones. Yet it is necessary that something convey this influence, and this is the spirit. And this is why, etc.
1. On to the arguments. To the first, one must respond that there are two things to consider in spirit, namely, the manner of the mixture and the impression of the soul. With respect to the manner of the mixture, the heavy dominates in spirit, but with respect to the impression of the soul this spirit receives an aptitude for motion. Thus, although materially it is heavy and dark, because to some extent it comes forth from heavy mixed bodies, nevertheless, formally, it is light and clear from the soul's irradiation.
2. To the second argument one must reply that spirit is not required as a medium uniting soul and body, since they unite themselves to one another. Rather, spirit is required for the execution of the soul's operations, since the execution of motion and sensation occurs with a mediating spirit, and this is why one does not proceed to infinity.
3. To the third, one must respond that spirit is not more subtle than an element but rather is better proportioned for the operation of the soul than is fire or air, and this is why spirit is more necessary than an element.
-  "Flows in from": perhaps, "is influenced by." bodies. Therefore, this heat is not an elemental heat but an animal or celestial heat.