Key Arguments

• He was already being swayed by Nebridius and Vindicianus, who argued that ‘the art of forecasting the future is non-existent, but that human conjectures often have the power of chance’ and that astrologers ‘say so much that some of their predictions are fulfilled, not because the forecasters know but because merely by not keeping silent they hit on the truth.’
• The story of Firminus and the slave‑child shows two people born at ‘the identical time’ under carefully observed identical constellations, yet with utterly different social status and destinies—one a free, noble citizen advancing on ‘the world’s main roads’, the other remaining a slave under ‘the yoke of his condition’.
• From this he reasons that if he gave forecasts based on the same tables, he would have to give different predictions to be right, and the same predictions to be wrong: ‘after inspecting identical horoscopes I should give different forecasts in order to get it right, and that to offer identical forecasts would be to get it wrong.’
• He infers that the occasional accuracy of horoscopes must be due to luck: ‘From this I drew the certain inference that true predictions on the basis of horoscopes are given not by skill but by chance, while false forecasts are due not to lack of skill in the art but to chance error.’
• He generalizes the problem using the case of twins: they are born at virtually the same time so that ‘someone inspecting the identical tables ought to have been able to say that Esau and Jacob would have the same destiny’, yet their histories are clearly different, so a correct forecast cannot be grounded in the identical stellar data.

Source Quotes

In many respects this faith was still unformed and hesitant about the norm of doctrine. Yet my mind did not abandon it, but daily drank in more and more. vi (8) I had already rejected the fraudulent divinations and impious fantasies of the astrologers. May your mercies, my God, make grateful confession of that to you from the innermost parts of my soul!

You healed the obstinacy with which I withstood the acute old man Vindicianus and Nebridius the young man with a mind of marvellous quality. The one vehemently, the other with some hesitancy but great frequency, declared that the art of forecasting the future is non-existent, but that human conjectures often have the power of chance. The fortune-tellers say so much that some of their predictions are fulfilled, not because the forecasters know but because merely by not keeping silent they hit on the truth.

The one vehemently, the other with some hesitancy but great frequency, declared that the art of forecasting the future is non-existent, but that human conjectures often have the power of chance. The fortune-tellers say so much that some of their predictions are fulfilled, not because the forecasters know but because merely by not keeping silent they hit on the truth. Your providence brought me a friend.

This could not pass unobserved by the slave-girl’s owner, who took pains to know the most precise details when his bitches were producing puppies. The two men made exact observations, the one of his wife, the other of his maidservant, for the days and hours and minutes, and it so came about that the women both had their infants at the identical time. So they had to make the same horoscopes for each newborn child identical to the minute, one for his son, the other for the little slave.

Therefore it followed that after inspecting identical horoscopes I should give different forecasts in order to get it right, and that to offer identical forecasts would be to get it wrong. From this I drew the certain inference that true predictions on the basis of horoscopes are given not by skill but by chance, while false forecasts are due not to lack of skill in the art but to chance error. (10) Starting from the approach to the subject which this story gave me, I ruminated further on these phenomena.

Key Concepts

• I had already rejected the fraudulent divinations and impious fantasies of the astrologers.
• the art of forecasting the future is non-existent, but that human conjectures often have the power of chance.
• The fortune-tellers say so much that some of their predictions are fulfilled, not because the forecasters know but because merely by not keeping silent they hit on the truth.
• the women both had their infants at the identical time.
• From this I drew the certain inference that true predictions on the basis of horoscopes are given not by skill but by chance, while false forecasts are due not to lack of skill in the art but to chance error.

Context

Book VII, section vi (8–10): Augustine recalls the arguments of Vindicianus and Nebridius, narrates the case of Firminus and a slave born at the same instant, and then reflects further (including on twins like Esau and Jacob) to dismantle belief in astrology as an art.