St. Augustine on Astrology

When he was younger Augustine practiced Astrology until his friend Firminus told him about two people he knew born at the same time, one born of a rich family and one of a slave. Augustine realized that if he had to make predictions for their lives:

The realization that after inspecting the same data I would either have to make divergent predictions in order to give a true answer, or else make the same prediction in the two cases and thereby speak falsely, was to me most certain evidence that when true predictions were offered by diviners who studied horoscopes, such things were the product of luck, not skill; but when false predictions were made, they resulted not from the practitioners lack of skill, but from his luck letting him down.

He went on to consider the case of twins:

At the birth of twins, then it usually happens that both are delivered from the womb with only a short interval of time between them; and however great the influence this space of time may be alleged to have in the course of nature, it cannot be measured by human observation and certainly cannot be registered in the charts which an astrologer will later study with a view to making a true forecast. And true it will not be, because anyone who had examined the one same birth horoscope that applied to Esau and Jacob would have been obliged to foretell the same fate for both of them, whereas in fact their destinies were different. The astrologer would therefore have been wrong; or, if he spoke truly and foretold different things for each, he would have done so on the basis of the same data. he could speak the truth only by chance, then, not by skill.

He concludes:

For in truth it is you, Lord, who are at work, you, the supremely just ruler of the universe, though those who consult astrologers and those who are consulted know it not. By your secret inspiration you make each inquirer hear what befits him, as your unfathomable judgment shall justly assess our souls’ secret deserving. Let no human being challenge you, “What is this?” or “Why that?” Let him not ask; no, let him not ask, for he is but human.