Sibling

Lilly's third house is a list that looks miscellaneous and is not: brethren, sisters, kindred, neighbours, short journeys, letters and rumours. What holds it together is proximity. The third is the house of everything close at hand and reachable without ceremony, and a sibling is the type case: a person of the same household and the same generation, neither above the native nor below.

Mercury is the general significator, which follows from the same idea. Mercury governs speech, messages, the short errand and the exchange of news, which is what the third house is for. The sign on the third cusp and the planet ruling it supply the particulars: how many, of what temperament, and on what terms.

The same place carries a much older name. In the Greek scheme the third is Thea, the Goddess, paired with the ninth, Theos, the God, and the Moon has its joy there. Those names sit oddly beside brethren and short journeys, and the mismatch is a useful reminder that the twelve places held different content in the Hellenistic system than the medieval catalogue later gave them. It is why some traditional astrologers still read the third as much for the Moon's affairs, the body and the daily round, as for siblings.

A reading that uses both layers has to keep them apart. The Goddess and the brother are not in one house by coincidence; they are two settlements of a single slot, several centuries apart.

Sources Christian AstrologyWilliam Lilly with Hellenistic Astrology: The Study of Fate and FortuneChris Brennan

Ptolemy gives brothers and sisters a chapter of their own in the third book, and he does not read them from a third house. He reads them from the parents, on the plain ground that siblings are the other children of the same parents, and takes the maternal place as his starting point.

This is a different kind of astrology from the house catalogue, and worth seeing clearly. The Hellenistic method asks what a thing is derived from and works outward. The medieval method assigns each subject a fixed compartment and looks in it. Neither is a corruption of the other. They are two solutions to the problem of getting from a sky to a life, and the second is far easier to teach, which is a large part of why it prevailed.

The two can also be run together, and traditional practice often does. A reader may take the third house for the sibling relationship as the native experiences it and Ptolemy's derivation for the family as a fact of birth, then treat a disagreement between them as information rather than as a mistake.

What neither method delivers is a count that can be relied on. Both describe ways of estimating the number of siblings from the planets in the relevant place, and both hedge the estimate with so many conditions that it stops behaving like a number. Astrologers who have promised an exact count from a chart have been embarrassed in every century, and the honest reading of the tradition is that counting is among the things it does worst.