II. To the Initial Arguments

52. To the argument [n.41] I say that fire always remains pure in itself with natural purity, because it is supremely active (such that it would at once convert into itself anything of an extraneous nature that would ascend to that region [of fire]), and because nothing rises by the action of heavenly bodies to the region of pure fire, so as thus to make fire impure. Now it is specifically this impurity from the smoke of sacrifices offered to idols and from infection from the sins of men that does not ascend to the sphere of fire, because neither that smoke nor any other infection from impure acts can ascend to the fire. But this purifying is posited because of the impurity of the air that is contracted from acts of human sin; therefore, it does not follow that the fire purifies itself.