Jacques Maritain Center
The movement of the heavenly bodies [i.e. of the crystal spheres which carry sun, moon and stars] is uniform [semper est eodem modo]. If then the effects of the heavenly bodies on these sublunary bodies were produced of necessity, the phenomena of sublunary bodies would be uniform. But they are not uniform, but happen only for the most part. Therefore they do not happen of necessity.' (Contra Gentiles, iii. 86, n. 3). This characteristic bit of ancient Scholasticism is explained in Of God and His Creatures, notes on pp. 184, 254.