Ten Treatises on Astronomy (Book of Astronomy)

¶ Chapter nine against those who said that the science of the stars is not useful, but rather harmful, because it brings sadness and anguish to those who have foreseen future misfortunes, causing them to grieve for that reason before the hardship actually happens to them.

There is another argument made by those who claim that the judgments of the stars have no value; that there is no utility in them, but rather harm. They argue that even if this science were true and its judgments valid, it is still more damaging than useful. This is because if some heavy burden that is destined to happen is foreseen from afar, it strikes a person with fear and sadness long before the time of pain, lasting until the evil actually befalls them. Afterward, they must still be sad, grieve, and lament anyway. They argue the astrologer cannot turn away that burden which is coming according to the stars; and even if he could turn it away, he could not at least turn away the anger and anguish that the person would suffer until the hour of its arrival.

To these people, one can respond in a familiar way: namely, that they do not know what they are talking about. It appears they are ignorant of how great the dignity and utility of this wisdom actually is; for if they knew, they would not say such things. For if some evil hangs over a man which is destined to come according to the stars, and he has foreknowledge of that future evil, he will see what kind of evil it is and of what species, and he can set himself against it. For Ptolemy Claudius Ptolemy, the 2nd-century mathematician and astronomer whose works formed the basis of medieval astrology. says in the Centiloquium original: "centiloquio"; the Centiloquy is a famous collection of 100 astrological aphorisms traditionally attributed to Ptolemy. that the best astrologer can avert many evils that are destined to happen according to the stars.

Future events are either universal or particular. Universal events include things like winter, summer, heat, cold, and disturbances of the air—such as rain, snow, hail, and plagues—as well as mortality, famine, barrenness, the abundance of earthly goods, and the like. Among these universal things, some are known only by the wise, while others are known not only by the wise but also by the common people. The wise know them through their diligence, specifically through this science of the stars. Laypeople and others unskilled in this science know certain future universal events through long experience, having seen them in their own times or heard of them from others older than themselves.

For they observe that in climates where the horizon reflects toward the north, the cold grows stronger when the sun enters Gemini and lasts until it enters Virgo The author is describing how the sun's position in the zodiac correlates with seasonal shifts in specific geographic "climates" or latitudes.—though the weather may be more or less different at other times. Therefore, in the summer, when they feel the heat, they say that in such a time there will be cold, snows, rains, winds, and the like. Then they provide themselves with grain, wine, wood, clothing, and other necessities with which they can repel the hardships of that time. Those who do not have houses strive to build them so they can flee the rain, snow, and other coming adversities. If these things were not known, they would not support themselves with the aforementioned necessities, and thus it could be the cause of their death. It remains, therefore, that the foreknowledge of future things is valuable.

Similarly, they know through the aforementioned experiences at what times they ought to sow so that they may harvest in the future, from which they can lead their lives according to the different species of various things. They also plant trees in the times in which they are accustomed to seeing them thrive. For every species of seed or plant is not sown or planted equally in all seasons of the year, nor in every region at the same time of year. For planting is done one way in Spain, another in England, another in Lombardy, another in Romania, another in Apulia, another in Asia, another in Ethiopia, another in the Alps, another in the plains, another in winter, and another in summer.

And some things are sown and planted in one season and others in another; each of them in the time appropriate to it, in which future utility is hoped for. This varies according to different regions and different locations. The experts of these places foresee all these things so accurately that they very rarely fail; therefore, the foreknowledge of future things is useful.

But some might then arise—one of whom was that fool—and say that these things do not happen from the impressions of the planets. One should not even argue with them, because they do not consider that every region and every location grows hot due to the approach of the sun, and grows cold due to the sun’s removal. Because of the sun's extreme proximity, a region dries up, and because of its extreme distance, it is chilled too much. Thus, people know not to sow every seed or plant every tree during such excesses of heat or cold. Those who use this knowledge foresee that things will happen this way because of the long experience they have seen and used. If they did not know this, they would not know in which seasons they should do the things mentioned above, and thus they would waste their expense and labor.

Furthermore, regarding other universal events that happen to everyone in any climate or region: some can be avoided, and some cannot. However, their effects can be diminished or altered in such a way that they can be useful to those who foresaw them. Not all these things can be known except by those skilled in this science; yet some of them can be known by skilled doctors, as Hippocrates original: "hypocras" mentions in his Aphorisms.

Indeed, the things known by astrologers that cannot be foreseen by the common people are many: such as plagues, famine, barrenness, scarcity, and sickness; the mortality of both rational beings i.e., humans and brute animals; or rain, snow, hail, and excessive heat or cold passing beyond measure. He who has foreknowledge of these can protect himself, and thus the foreknowledge of the future is useful and not harmful. Foreknowledge does not avoid an unknown evil, but a known evil can be avoided if it is foreseen, especially from afar.

For when someone foresees that grain will be expensive in the future, he can buy it for himself while it is cheap and save it until the time when it will be useful to him; the same applies to wine, oil, and similar things. When he has foreseen a future mortality in some climate or region, he can move himself and depart from that region to go to another where the plague will not threaten that year. When he foresees a future sickness in some region, he can oppose the cause threatening that sickness, or similarly go to another region to remain healthy. Thus, the foreknowledge of that thing will be the cause of safety for the one foreseeing it and a means of escaping future danger.

Similarly, if someone foresees future rain, he can flee to shelter and to places where the rain cannot soak him before it arrives. Likewise, when someone is about to go to sea and foresees a future wind or a great storm, he can reach a port where he may be safe before the storm arrives, so that he does not suffer shipwreck; or he may choose not to enter the sea until the dangerous time has passed.

Likewise, if a question is asked about someone who is sick, or if the astrologer knows the beginning of that illness, he can know in advance whether the sick person is likely to recover or die. If he foresees that the person will die, he can predict the death to him. Thus, the sick person—who perhaps did not believe he would die from that illness—may take up penance and confess his sins, so that Jesus Christ our Lord may provide for him in the future life (that is, the imperceptible life). He will also be able to make his will, arrange his household, organize his affairs, and settle with his creditors and debtors. If he did not do this, there might be danger for those who remain after him.