It is common to read that a certain astrological factor has “rulership” over something. This can sound very mysterious but is actually quite simple – it just means that the energy represented by the astrological symbol has an affinity with the item. This is called the rule of similars or the doctrine of correspondences. You could also say that they partake of the same essence; they are essentially the same.
Consider your home. This is associated with the Moon and what ever your chart looked like you would look to the Moon to tell you about your home and this is its natural ruler. You could also look to the IC as the bottom of the chart and cusp of the fourth house. The planet you would consider would be the ruler of the sign on the IC, the house ruler. If Cancer was on the IC the Moon would be both the natural ruler and the house ruler. If Virgo was on the IC the house ruler would be Mercury.
- Natural rulership: the meaning of the astrological symbol is linked to the actual object.
- Derived rulership: determined by the signs which appear on house cusps.
Derived rulership is specific to the particular chart. For instance Mercury will always say something about communication but the third house ruler is not necessarily Mercury. Accurate delineation comes from appreciating the differences.
Just to add to the confusion, Rulership by sign is one of the essential dignities. Modern astrologers only use rulership by sign but there is also rulership by exaltation, triplicity, term and face.