Book 2, Chapter 43

90 “What incredible delirium! Not every error deserves the name of folly. Even Diogenes the Stoic concedes something to these men: that they can predict at least what a person’s natural disposition will be and what he will be best suited to do. The rest of what they profess to know, he says, cannot possibly be known. Twins, after all, are alike in appearance, but generally unlike in life and fortune. Procles and Eurysthenes, the Spartan kings, were twin brothers.

91 “Yet they did not even live the same number of years: Procles’s life was a year shorter, and he far surpassed his brother in the glory of his achievements. But even what that excellent man Diogenes concedes to the Chaldeans—as though betraying his own case—I deny can be ascertained. Since, as they themselves say, the moon governs births, and the Chaldeans observe and record as birth stars whatever heavenly bodies appear in conjunction with the moon, they use the most deceptive sense of sight to judge things they ought to see by reason and the mind. Mathematical reasoning, which these people ought to have mastered, teaches how low the moon travels, almost touching the earth; how far it lies from the nearest planet, Mercury, and how much farther from Venus; then how another interval separates it from the sun, whose light is believed to illuminate it. The remaining three distances are boundless and immeasurable: from the sun to Mars, from Mars to Jupiter, from Jupiter to Saturn, and beyond that to the heavens themselves, the universe’s outermost and final boundary.

90 “What unbelievable madness! Not every mistake, after all, deserves to be called stupidity. Even Diogenes the Stoic allows them something. He says they can predict only what someone's natural character will be and what he will be best suited for. But he denies that the other things they claim can possibly be known. Twins look alike, he says, but usually have different lives and fortunes. Procles and Eurysthenes, the Spartan kings, were twin brothers.

91 “Yet even the lengths of their lives differed. Procles' life was a year shorter, and he far outshone his brother in the fame of his achievements. Diogenes is an excellent man, but I deny that we can know even what he allows the Chaldeans, as if he were betraying our case. They themselves say that the moon controls births. The Chaldeans watch and record as birth stars any stars that seem close to the moon. So they judge by sight, the most misleading of senses, what they should grasp with thought and reason. Mathematical reasoning, which they ought to know, teaches us how low the moon travels, almost touching the earth. We learn that even Mercury, the closest planet, lies far from the moon, and Venus farther still. The sun, believed to supply its light, is yet another distance away. After that come three immeasurably vast gaps: from the sun to Mars, from there to Jupiter, from Jupiter to Saturn, and from there to the sky itself, the farthest, outermost boundary of the universe.