The heaven of Saturn has two properties by which it may be compared to Astrology: one is the slowness of its movement through the 12 signs, for according to the writings of the astrologers, a time of more than 29 years is required for its revolution; the other is that it is high above all the other planets.

And these two properties are found in Astrology: for [...] to master this science a very great span of time passes, both because of its handmaids, which are more numerous than those of any of the above-mentioned sciences, and because of the experience required in it for making proper judgments.

Furthermore, it is far higher than all the others [...] by virtue of the nobility of its subject and by virtue of its certainty [...] And if anyone believes that there is a flaw in it, it does not pertain to the science, but as Ptolemy says, it results from our negligence, and so must be attributed to that.

Convivio II, XIII, 28-30