Soul

The third book of the Tetrabiblos contains a chapter on the quality of the soul, and it opens with a division that shaped every later astrological account of the person. The soul has two parts. The rational part is governed by Mercury. The sensitive or irrational part is governed by the Moon.

The division is not Ptolemy's invention. It is the standard philosophical anatomy of his period, and he is applying astrology to a psychology already in general circulation. What astrology adds is a way of examining each part separately. To read the rational soul, examine Mercury: its sign, its aspects, whether it is direct or retrograde, and which planets configure to it. To read the sensitive soul, examine the Moon in the same way. A chart in which the two are in good condition and in aspect describes a person whose thinking and whose feeling are in communication. A chart in which they are unrelated describes one in which they are not.

The scheme carries a further refinement. Ptolemy takes the planets that aspect Mercury and the Moon as the ones that colour each part, so that Saturn makes the rational soul careful and hard, Jupiter makes it expansive, Mars quick, Venus soft. The two significators supply the faculties and the aspecting planets supply the character.

What the chapter does not do is offer a single significator for the soul as a whole. That is a later development, and this entry keeps the two accounts apart.

Alongside Ptolemy's two part soul runs a different association, which gives the soul to the Sun. It comes from a different intellectual lineage and it should not be blended with the first without saying so.

In the Neoplatonic and Hermetic material that grew up alongside technical astrology, the Sun is the visible image of the intelligible good, the heart of the cosmos, and the source of the light by which everything else is seen. Transferred to a nativity, the Sun becomes the ruling principle of the person: what a life is fundamentally for, and the part of it not reducible to temperament or circumstance. Later Western astrology inherited this reading, and modern popular astrology has made it dominant, which is why a person's sign now means their Sun sign and nothing else.

The two accounts answer different questions. Ptolemy is asking how a person thinks and feels, and gets two significators because thinking and feeling are two operations. The solar account is asking what a person essentially is, and gets one because that is a question with one answer or none.

The atlas records both under this entry and keeps them distinct. Treating the Sun as the soul and then applying Ptolemy's technique to it produces a reading that neither source supports, and the mixture is common enough in modern writing to be worth naming.

Sources Hermetica: The Greek Corpus Hermeticum and the Latin AsclepiusBrian P. Copenhaver with A History of Western AstrologyNicholas Campion