HKB
it is called "geomancy," if in water "hydromancy," if in the air "aeromancy," if in fire "pyromancy," if in the entrails of animals sacrificed on the altars of demons, "aruspicy."
The divination which is practiced without express invocation of the demons is of two kinds. The first is when, with a view to obtain knowledge of the future, we take observations in the disposition of certain things. If one endeavor to know the future by observing the position and movements of the stars, this belongs to "astrologers," who are also called "genethliacs," because they take note of the days on which people are born. If one observe the movements and cries of birds or of any animals, or the sneezing of men, or the sudden movements of limbs, this belongs in general to "augury," which is so called from the chattering of birds (avium garritu), just as "auspice" is derived from watching birds (avium inspectione). These are chiefly wont to be observed in birds, the former by the ear, the latter by the eye. If, however, these observations have for their object men's words uttered unintentionally, which someone twist so as to apply to the future that he wishes to foreknow, then it is called an "omen": and as Valerius Maximus [*De Dict. Fact. Memor. i, 5] remarks, "the observing of omens has a touch of religion mingled with it, for it is believed to be founded not on a chance movement, but on divine providence. It was thus that when the Romans were deliberating whether they would change their position, a centurion happened to exclaim at the time: 'Standard-bearer, fix the banner, we had best stand here': and on hearing these words they took them as an omen, and abandoned their intention of advancing further." If, however, the observation regards the dispositions, that occur to the eye, of figures in certain bodies, there will be another species of divination: for the divination that is taken from observing the lines of the hand is called "chiromancy," i.e. divination of the hand (because cheir is the Greek for hand): while the divination which is taken from signs appearing in the shoulder-blades of an animal is called "spatulamancy."
To this second species of divination, which is without express invocation of the demons, belongs that which is practiced by observing certain things done seriously by men in the research of the occult, whether by drawing lots, which is called "geomancy"; or by observing the shapes resulting from molten lead poured into water; or by observing which of several sheets of paper, with or without writing upon them, a person may happen to draw; or by holding out several unequal sticks and noting who takes the greater or the lesser, or by throwing dice, and observing who throws the highest score; or by observing what catches the eye when one opens a book, all of which are named "sortilege."
Accordingly it is clear that there are three kinds of divination. The first is when the demons are invoked openly, this comes under the head of "necromancy"; the second is merely an observation of the disposition or movement of some other being, and this belongs to "augury"; while the third consists in doing something in order to discover the occult; and this belongs to "sortilege." Under each of these many others are contained, as explained above.
Reply Obj. 1: In all the aforesaid there is the same general, but not the same special, character of sin: for it is much more grievous to invoke the demons than to do things that deserve the demons' interference.
Reply Obj. 2: Knowledge of the future or of the occult is the ultimate end whence divination takes its general formality. But the various species are distinguished by their proper objects or matters, according as the knowledge of the occult is sought in various things.