Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that divination by the stars is not unlawful. It is lawful to foretell effects by observing their causes: thus a physician foretells death from the disposition of the disease. Now the heavenly bodies are the cause of what takes place in the world, according to Dionysius (Div. Nom. iv). Therefore divination by the stars is not unlawful.

Objection 2: Further, human science originates from experiments, according to the Philosopher (Metaph. i, 1). Now it has been discovered through many experiments that the observation of the stars is a means whereby some future events may be known beforehand. Therefore it would seem not unlawful to make use of this kind of divination.

Objection 3: Further, divination is declared to be unlawful in so far as it is based on a compact made with the demons. But divination by the stars contains nothing of the kind, but merely an observation of God's creatures. Therefore it would seem that this species of divination is not unlawful.

On the contrary, Augustine says (Confess. iv, 3): "Those astrologers whom they call mathematicians, I consulted without scruple; because they seemed to use no sacrifice, nor to pray to any spirit for their divinations which art, however, Christian and true piety rejects and condemns."

I answer that, As stated above (Articles 1,2), the operation of the demon thrusts itself into those divinations which are based on false and vain opinions, in order that man's mind may become entangled in vanity and falsehood. Now one makes use of a vain and false opinion if, by observing the stars, one desires to foreknow the future that cannot be forecast by their means. Wherefore we must consider what things can be foreknown by observing the stars: and it is evident that those things which happen of necessity can be foreknown by this mean,: even so astrologers forecast a future eclipse.

However, with regard to the foreknowledge of future events acquired by observing the stars there have been various opinions. For some have stated that the stars signify rather than cause the things foretold by means of their observation. But this is an unreasonable statement: since every corporeal sign is either the effect of that for which it stands (thus smoke signifies fire whereby it is caused), or it proceeds from the same cause, so that by signifying the cause, in consequence it signifies the effect (thus a rainbow is sometimes a sign of fair weather, in so far as its cause is the cause of fair weather). Now it cannot be said that the dispositions and movements of the heavenly bodies are the effect of future events; nor again can they be ascribed to some common higher cause of a corporeal nature, although they are referable to a common higher cause, which is divine providence. on the contrary the appointment of the movements and positions of the heavenly bodies by divine providence is on a different principle from the appointment of the occurrence of future contingencies, because the former are appointed on a principle of necessity, so that they always occur in the same way, whereas the latter are appointed on a principle of contingency, so that the manner of their occurrence is variable. Consequently it is impossible to acquire foreknowledge of the future from an observation of the stars, except in so far as effects can be foreknown from their causes.

Now two kinds of effects escape the causality of heavenly bodies. In the first place all effects that occur accidentally, whether in human affairs or in the natural order, since, as it is proved in Metaph. vi , an accidental being has no cause, least of all a natural cause, such as is the power of a heavenly body, because what occurs accidentally, neither is a "being" properly speaking, nor is "one"---for instance, that an earthquake occur when a stone falls, or that a treasure be discovered when a man digs a grave---for these and like occurrences are not one thing, but are simply several things. Whereas the operation of nature has always some one thing for its term, just as it proceeds from some one principle, which is the form of a natural thing.

In the second place, acts of the free-will, which is the faculty of will and reason, escape the causality of heavenly bodies. For the intellect or reason is not a body, nor the act of a bodily organ, and consequently neither is the will, since it is in the reason, as the Philosopher shows (De Anima iii, 4,9). Now no body can make an impression on an incorporeal body. Wherefore it is impossible for heavenly bodies to make a direct impression on the intellect and will: for this would be to deny the difference between intellect and sense, with which position Aristotle reproaches (De Anima iii, 3) those who held that "such is the will of man, as is the day which the father of men and of gods," i.e. the sun or the heavens, "brings on" .

Hence the heavenly bodies cannot be the direct cause of the free-will's operations. Nevertheless they can be a dispositive cause of an inclination to those operations, in so far as they make an impression on the human body, and consequently on the sensitive powers which are acts of bodily organs having an inclination for human acts. Since, however, the sensitive powers obey reason, as the Philosopher shows (De Anima iii, 11; Ethic. i, 13), this does not impose any necessity on the free-will, and man is able, by his reason, to act counter to the inclination of the heavenly bodies.

Accordingly if anyone take observation of the stars in order to foreknow casual or fortuitous future events, or to know with certitude future human actions, his conduct is based on a false and vain opinion; and so the operation of the demon introduces itself therein, wherefore it will be a superstitious and unlawful divination. On the other hand if one were to apply the observation of the stars in order to foreknow those future things that are caused by heavenly bodies, for instance, drought or rain and so forth, it will be neither an unlawful nor a superstitious divination.

Wherefore the Reply to the First Objection is evident.

Reply to Objection 2: That astrologers not unfrequently forecast the truth by observing the stars may be explained in two ways. First, because a great number of men follow their bodily passions, so that their actions are for the most part disposed in accordance with the inclination of the heavenly bodies: while there are few, namely, the wise alone, who moderate these inclinations by their reason. The result is that astrologers in many cases foretell the truth, especially in public occurrences which depend on the multitude. Secondly, because of the interference of the demons. Hence Augustine says (Gen. ad lit. ii, 17): "When astrologers tell the truth, it must be allowed that this is due to an instinct that, unknown to man, lies hidden in his mind. And since this happens through the action of unclean and lying spirits who desire to deceive man for they are permitted to know certain things about temporal affairs." Wherefore he concludes: "Thus a good Christian should beware of astrologers, and of all impious diviners, especially of those who tell the truth, lest his soul become the dupe of the demons and by making a compact of partnership with them enmesh itself in their fellowship."

This suffices for the Reply to the Third Objection.

Articulus 5

Argumentum 1

Ad quintum sic proceditur. Videtur quod divinatio quae fit per astra non sit illicita. Licitum enim est ex consideratione causarum praenuntiare effectus, sicut medici ex dispositione aegritudinis praenuntiant mortem. Sed corpora caelestia sunt causa eorum quae fiunt in hoc mundo, ut etiam dionysius dicit, IV cap. De div. Nom..

Ergo divinatio quae fit per astra non est illicita.

Argumentum 2

Praeterea, scientia humana ex experimentis originem sumit, ut patet per philosophum, in principio metaphys..

Sed per multa experimenta aliqui compererunt ex consideratione siderum aliqua futura posse praenosci.

Ergo non videtur esse illicitum tali divinatione uti.

Argumentum 3

Praeterea, divinatio dicitur esse illicita inquantum innititur pacto cum Daemonibus inito. Sed hoc non fit in divinatione quae fit per astra, sed solum consideratur dispositio creaturarum dei.

Ergo videtur quod huiusmodi divinatio non sit illicita.

Sed Contra

Sed contra est quod Augustinus dicit, in IV confess., illos planetarios quos mathematicos vocant, consulere non desistebam, quod quasi nullum esset eis sacrificium, et nullae preces ad aliquem spiritum ob divinationem dirigerentur. Quod tamen christiana et vera pietas expellit et damnat.

Corpus

Respondeo dicendum quod, sicut dictum est, divinationi quae ex opinione falsa vel vana procedit, ingerit se operatio Daemonis, ut hominum animos implicet vanitati aut falsitati. Vana autem aut falsa opinione utitur si quis ex consideratione stellarum futura velit praecognoscere quae per ea praecognosci non possunt. Est igitur considerandum quid per caelestium corporum inspectionem de futuris possit praenosci.

Et de his quidem quae ex necessitate eveniunt, manifestum est quod per considerationem stellarum possunt praenosci, sicut astrologi praenuntiant eclipses futuras. Circa praecognitionem vero futurorum eventuum ex consideratione stellarum, diversi diversa dixerunt.

Fuerunt enim qui dicerent quod stellae significant potius quam faciant ea quae ex earum consideratione praenuntiantur.

Sed hoc irrationabiliter dicitur. Omne enim corporale signum vel est effectus eius cuius est signum, sicut fumus significat ignem, a quo causatur, vel procedit ab eadem causa, et sic, dum significat causam, per consequens significat effectum, sicut iris quandoque significat serenitatem, inquantum causa eius est causa serenitatis. Non autem potest dici quod dispositiones caelestium corporum et motus sint effectus futurorum eventuum.

Nec iterum possunt reduci in aliquam superiorem causam communem quae sit corporalis. Possunt autem reduci in unam causam communem quae est providentia divina, sed alia ratione disponuntur a divina providentia motus et situs caelestium corporum, et alia ratione eventus contingentium futurorum; quia illa disponuntur secundum rationem necessitatis, ut semper eodem modo proveniant; haec autem secundum rationem contingentiae, ut variabiliter contingant. Unde non potest esse quod ex inspectione siderum accipiatur praecognitio futurorum nisi sicut ex causis praecognoscuntur effectus.

Duplices autem effectus subtrahuntur causalitati caelestium corporum. Primo quidem, omnes effectus per accidens contingentes, sive in rebus humanis sive in rebus naturalibus.

Quia, ut probatur in VI metaphys., ens per accidens non habet causam, et praecipue naturalem, cuiusmodi est virtus caelestium corporum. Quia quod per accidens fit neque est ens proprie neque unum, sicut quod, lapide cadente, fiat terraemotus, vel quod, homine fodiente sepulcrum, inveniatur thesaurus; haec enim, et huiusmodi, non sunt unum, sed simpliciter multa.

Operatio autem naturae semper terminatur ad aliquid unum, sicut et procedit ab uno principio, quod est forma rei naturalis.

Secundo autem, subtrahuntur causalitati caelestium corporum actus liberi arbitrii, quod est facultas voluntatis et rationis.

Intellectus enim, sive ratio, non est corpus nec actus organi corporei; et per consequens nec voluntas, quae est in ratione, ut patet per philosophum, in III de anima.

Nullum autem corpus potest imprimere in rem incorpoream. Unde impossibile est quod corpora caelestia directe imprimant in intellectum et voluntatem, hoc enim esset ponere intellectum non differre a sensu; quod Aristoteles, in libro de anima, imponit his qui dicebant quod talis voluntas est in hominibus qualem in die inducit pater virorum deorumque, scilicet sol vel caelum. Unde corpora caelestia non possunt esse per se causa operum liberi arbitrii. Possunt tamen ad hoc dispositive inclinare, inquantum imprimunt in corpus humanum, et per consequens in vires sensitivas, quae sunt actus corporalium organorum, quae inclinant ad humanos actus.

Quia tamen vires sensitivae obediunt rationi, ut patet per philosophum, in III de anima et in I ethic., nulla necessitas ex hoc libero arbitrio imponitur, sed contra inclinationem caelestium corporum homo potest per rationem operari. Si quis ergo consideratione astrorum utatur ad praecognoscendos futuros casuales vel fortuitos eventus, aut etiam ad cognoscendum per certitudinem futura opera hominum, procedet hoc ex falsa et vana opinione. Et sic operatio Daemonis se immiscet. Unde erit divinatio superstitiosa et illicita. Si vero aliquis utatur consideratione astrorum ad praecognoscendum futura quae ex caelestibus causantur corporibus, puta siccitates et pluvias et alia huiusmodi, non erit illicita divinatio nec superstitiosa.

Ad 1

Et secundum hoc patet responsio ad primum.

Ad 2

Ad secundum dicendum quod hoc quod astrologi ex consideratione astrorum frequenter vera praenuntiant, contingit dupliciter.

Uno quidem modo, quia plures hominum passiones corporales sequuntur, et ideo actus eorum disponuntur, ut in pluribus, secundum inclinationem caelestium corporum, pauci autem sunt, idest soli sapientes, qui ratione huiusmodi inclinationes moderentur.

Et ideo astrologi in multis vera praenuntiant, et praecipue in communibus eventibus, qui dependent ex multitudine. Alio modo, propter Daemones se immiscentes.

Unde Augustinus dicit, in II super Gen. Ad litt., fatendum est, quando a mathematicis vera dicuntur, instinctu quodam occultissimo dici, quem nescientes humanae mentes patiuntur. Quod cum ad decipiendos homines fit, spirituum immundorum et seductorum operatio est, quibus quaedam vera de temporalibus rebus nosse permittitur.

Unde concludit, quapropter bono christiano sive mathematici, sive quilibet impie divinantium, et maxime dicentes vera, cavendi sunt, ne consortio Daemoniorum animam deceptam pacto quodam societatis irretiant.

Ad 3

Et per hoc patet responsio ad tertium.