Ptolemy's Method for Determining the Hyleg
Claudius Ptolemy, generally regarded as being the father of Western astrrology, states in his Tetrabiblios that the Hyleg is the planet with the greatest essential dignity in five important chart positions:
1) The degree of the
Sun
2) The degree of the
Moon
3) The degree of the
Ascendant
4) The
Part of Fortune
5) The
Prenatal Syzygy - the degree of the
New Moon or
Full Moon before birth (New Moon if the natal Moon is waxing, and Full Moon if the natal Moon is waning).
When it comes to matters of essential planetary dignities, classical astrologers like Ptolemy had a much more complex and involved system for reckoning them than modern astrology. In addition to the modern dignities of
rulership and
exaltation, the ancients also figured in the
triplicity rulers as well as the lords of the
terms and
faces.
In addition, they had a point system for tallying up or measuring the relative strength or debility of a planet, based on its essential dignities and debilities.
Five points was given for a planet being the
domicile ruler,
four points for it being in
exaltation,
three points for it being the
triplicity ruler,
two points for being the
term ruler, and one point for being the
face ruler. The planet with the greatest essential dignity is called the
Almuten.
With Ptolemy's method the Hyleg, being the planet with the greatest essential dignity over the above five key positions in the natal horoscope, functions like a Grand Almuten of the entire chart. To score and determine exactly what this Grand Almuten is, put the symbols for the seven classical planets across the top of the page. Under each, write down in a vertical column all the points each planet receives regarding each of the above five positions. At the end, tally up the total number of points for each planet; the planet with the highest score or total overall wins.
As a reference chart for scoring, especially regarding the more obscure classical dignities, I provide you with the following link. It's a chart of the essential planetary dignities according to Ptolemy, with an explanatory article of several pages that follows it:
http://www.skyscript.co.uk/dig2.html
One additional qualification remains: the planet must also be in a Hylegaical house. For purposes of selecting the Hyleg, Ptolemy considered the first five degrees above the horizon to be functionally part of the First House; a First House planet, to be Hyleg, must also be in the same sign as the Ascendant degree. If no planet can qualify to be the Hyleg, then the Ascendant itself becomes the Hyleg.
Once the Hyleg has been determined, it is analyzed according to its various accidental dignities to determine the native's potential for health and longevity. The point system for scoring these accidental dignities and debilities is also in the the Skyscript article that accompanies the chart on the above link. Accidental dignities add to the Hyleg's potential for health and vitality, whereas accidental debilities detract from it.
The 17th century English astrologer
William Lilly also had his method for determining the Hyleg. It can also be found in the above Skyscript article.