De cometis

Avicenna: Air is the element of our bodies and spirits. And because of this, that it is an element, it is also an emanation coming to our spirits, and it is a cause of their betterment, not only as an element but also as a form. Wherefore, since air is mixed with the most subtle substances, fortified by celestial virtue as if by the seminal spirits of the stars, it is mixed with vital spirits and alters them, and they are incorporated into them, and their virtue is dilated. And they perform the operations of their stars in those predisposed to this, just as seeds perform by their virtues. Regarding this way of alteration, Avicenna speaks in the Canon, fourth book, on pestilential fever in this manner: "And when the celestial agent virtues and the terrestrial patient ones make humidity in the air, fumes and vapors are expelled to it, and they are dispersed and putrefy with weak heat. And the air, infected in this manner, coming to the heart, corrupts the complexion of the spirit which is in it. And the principle of all these is from the forms of the sky, which make necessary that which the ignorant arrival is. Wherefore it is necessary for the mixture of extraneous substances with the air, because of the necessity of the respiration of the same, to alter the heart, virtues, and spirits, from which all operations proceed, whence of necessity sicknesses and mortalities or healths follow."

Ptolemy said in the last word: "And the death of them will be as sudden as possible." As if he were to say: The death which a comet causes is for the most part sudden, because these substances of the comet are most subtle and almost absolute from elementary properties, on account of the excellence of the celestial ones, which, if they are discordant and contrary to the vital spirits, will be to them like a poison from a specific form, not altering them by complexion-based alterations, which putrefaction or another complexion-based dyscrasia would follow. But quickly and at once, by their own property, they take away or diminish the power of the vital spirit to give life. Thus, sudden death follows the taking away. But death after a success, without great change of the body from that which is healthy, follows the diminution. And regarding this also, Avicenna, wondering, says in the chapter on pestilential fever, in these words: "And sometimes in these fevers, heat is not perceived, and the pulse is not altered by great alteration, and with this it kills quickly, and physicians hesitate in its essence." For as much as the matter is more subtle and more absolute from elementary ones, by so much the more quickly and with fewer means and without annexed accidents following, does it produce its elementary operation, whatever it may be. Thus, things subtle and contrary to human nature and sublimated poisons, etc., kill quickly. For their penetration is easy. Thus also, the fifth essence the quintessence, without annexed things, suddenly brings health, as the ancient philosophers report.

Knowledge cannot be other than from the property of the spirit and the virtue producing it, since an effect is the participated likeness of its cause. Thus, therefore, souls follow bodies, as Aristotle says. Whence, because of diverse spirits and virtues altered in diverse ways, in diverse times, regions, and ages, there will be diversity in sensitive knowledges and affections, which diverse manners and customs follow. For of all