Part of Fortune

The Part of Fortune, or Lot of Fortune (Pars Fortunae, Greek Kleros Tyches), is the principal of the Hellenistic lots, calculated points derived from the positions of other factors in the chart. It is the most important and most widely used of these constructions, attested by name as early as the first-century writer Dorotheus of Sidon and treated at length afterward by Vettius Valens in the second century and Firmicus Maternus in the fourth, both of whom folded it into detailed techniques for reading a nativity. It belonged to a wider family of Hellenistic lots, including those of Spirit, Eros and Necessity, but Fortune alone endured as later astrologers narrowed their attention to it.

Medieval writers, working from Arabic and Persian transmissions of this Hellenistic material, came to call the whole category of lots the Arabic parts, a label the thirteenth-century Italian astrologer Guido Bonatti helped fix in Western usage even though the technique itself long predated Arabic astrology. Some scholars trace the lot's roots further back still, to the Hellenistic Hermetic text known as the Liber Hermetis, which several researchers date to Ptolemaic Egyptian temple astrology of perhaps the third century BCE, well before any of the surviving Greek astrological authors wrote about it by name.