1. First, through the disposition of the body, whose arrangement and organization is ordered according to a fittingness toward what is above. If therefore "he gave man an uplifted face and bade him gaze upon the heavens," and he looks upward: therefore the spirit is borne upward.
2. Likewise, all naturally desire happiness: but it is certain that no one can be happy in miseries, especially one to whom death comes unwillingly: therefore, if he cannot have happiness in this life, he is born to have it after this life as a separated spirit: therefore, etc. 3. Furthermore, our intellect is unmixed, whence it understands all things; therefore it does not depend on the body with respect to its act, therefore much less with respect to its being: therefore, when the body descends, it is possible for the spirit to ascend.
4. Likewise, by the reasoning of Ecclesiastes himself: because if some have good things and some have evil things, and we see that in the present evil things befall the good and good things befall the wicked: if therefore it is necessary to posit one ruler, it is necessary to posit another time and recompense, in which God judges the impious and the just. Since therefore our faith declares this, Ecclesiastes seems to have been a heretic who doubted this.
That it goes downward, however, seems apparent:
1. Through Scripture: because in Wisdom 9 it is said: The body which is corrupted weighs down the soul; therefore, if the soul is corrupted bodily, it is corrupted entirely.
2. Likewise, what suffers with the suffering dies with the dying: but the soul suffers with the body: therefore, etc.
3. Likewise, no substance is idle; therefore what takes away from something all operation takes away from it being and duration: but the soul loses all operation when the body is injured, which is evident because it loses the intellect, regarding which this seems less likely, as in the case of the mad: therefore, when the body is corrupted, it loses its substance.
I respond: it must be said that good souls ascend upward to reward, and that the souls of beasts descend downward into corruption — this our faith both declares and presupposes; and with this, reason and philosophy agree. Nevertheless, that reasoning and philosophy is both obscure and has many grounds for doubt; therefore almost no one, or very few, were able to attain true certitude concerning the immortality of the soul and its beatitude, unless faith had come to their aid. Whence even Plato, who held the soul to be immortal, nevertheless erred concerning beatitude, since he held that souls pass through the bodies of brute animals. — Ecclesiastes therefore neither denies nor doubts this, but says that this is difficult to demonstrate; and this is indeed true for the unbeliever.
2. 3. To what is objected concerning operation and co-suffering, it must be said that for something to be united to another, this occurs in two ways: either as a mover only, and then it can be separated with no change made in it; or as a mover and a perfection, and this again in two ways: either it does not have its own proper operation, as the soul of a brute animal, or it has its own proper operation, as the human soul. Since therefore the human soul is united to the body as perfection and mover, it suffers together with the suffering body; therefore it is also impeded when the body is impeded. But since it is joined separably, it is not necessary that it itself be corrupted: when every harmony is dissolved, the soul departs.