On Astrology

You should know, first of all, that the power of celestial bodies extends to the changeable bodies below them. As Augustine says: it is not wholly absurd to say that certain celestial influences are able to cause differences only in bodies (De civitate Dei v, 6). Therefore, if someone should use horoscopes for predicting bodily effects, such as storms or calm weather, the health or sickness of a body, or the abundance or sterility of crops, and similar things which depend on bodily and natural causes, in these cases the use of astrology does not appear to be sinful. For to some extent all men make use of the observation of celestial bodies. Farmers, for instance, sow and reap at certain times that are determined by the motion of the sun; sailors avoid journeying both during the full moon, and also during lunar eclipses; in the treatment of ailments, doctors observe critical days, which they determine according to the influence of the sun and the moon. For this reason, it is not unfitting to use astrology to determine bodily effects according to other more obscure observations of the stars.

Nevertheless, we ought to hold firmly that the will of man is not subject to the necessity of the stars. Otherwise, it would do away with free will; and if free will were taken away, good works would not be assigned to men for their merit, nor evil works for their fault. For this reason, all Christians should with utmost certainty hold that things which depend on the will of man, such as all human works, are not by necessity subject to the stars. Therefore, it is written: do not be terrified by the signs of heaven, which the nations fear (Jer 10:2).

But in order to draw all men into error, the Devil mingles himself into the activities of those who eagerly consult astrology. Therefore, Augustine remarks: we must admit that when the truth is spoken by astrologers, it is revealed by a certain very occult prompting, to which the human mind is subject without knowing it. And since it happens in order to deceive men, it is the work of unclean and lying spirits who are permitted knowledge of certain truths concerning temporal things (De Genesi ad litteram ii, 15). Consequently, Augustine says (De doctrina Christiana ii, 23) that such observations should be attributed to certain pacts entered into with demons. Keeping pacts and communion with demons should be entirely avoided by Christians, as the Apostle says: I do not wish you to be allies to demons (1 Cor 10:20). Therefore, it should be resolutely held that it is a grave sin to engage in astrology concerning those things which depend on the will of man.