Decanates - each sign divided into 10-degree division and assigned a ruler.Thus, Aries and Mars are assigned to the first third of Aries, Leo and the Sun to the second third, Sagittarius and Jupiter to the final third. A sign's primary ruler is always the decan ruler of the first ten-degrees. So Venus rules the first third of Taurus, Mercury the second third (Virgo), and Saturn the final third (Capricorn). A second system is also one of decanate rulership, but in this case, while the first third of Aries is ruled by Mars and the second third by the Sun, the remaining 34 thirds of the zodiac are ruled thereafter according to the Chaldean order of the planets; the last third of Aries is ruled by Venus; the first third of Taurus by Mercury, the second by the Moon, and the third by Saturn; the first third of Gemini by Jupiter, and then the order starts over again, repeating with Mars at the second third of Gemini. There are, however, two kinds of rulership by triplicity. The one just mentioned is a simple grouping of signs by element. Ptolemy proposes another, which is not a system of faces, best known today through his Table of Essential Dignities and Debilities, a system of sign classification for purposes of determining planetary strength. Ptolemy's triplicities provide each sign with two planetary rulers, one by day and one by night. The Sun rules all the fire signs by day, and Jupiter by night. Venus rules all the earth signs by day, and the Moon by night. Saturn rules all the air signs by day and Mercury by night. Finally, Mars rules all the water signs both by day and by night. Ptolemy's faces (ideoprosotoi) are something different. A planet is said to be in its own face when located in a house that is distant from the Moon or the Sun by the same number of houses as the sign it rules is distant from the sign ruled by the Moon or Sun respectively. To explain: Ptolemy uses a system of diurnal and nocturnal signs, assigning the Sun and the Moon to "natural" positions closest to the zenith, the Sun because of all the planets it produces the most heat,the Moon next to the Sun because it is the second most important body. Based on an Aries fiducial, this puts the Sun in Leo, generally the hottest (sunniest) time of year in the northern hemisphere. Cancer is the "house of the Moon," the second most powerful body, being adjacent to Leo at the zenith. Leo through Pisces are the diurnal signs. Capricorn to Aquarius (passing through Aries) are the noctural signs. So Virgo is adjacent to Leo and Gemini is adjacent to Cancer; both of these signs are the "houses" of Mercury, the next closest planet to the earth after the Sun and Moon. Then next to Virgo is Libra and next to Gemini is Taurus; both of these signs are the "houses" of Venus, the next planet out. It continues, Mars ascribed to nocturnally to Aries and diurnally to Scorpio, Jupiter ascribed to Pisces and Sagittarius, and finally Saturn ascribed to the last two signs, adjacent to each other and opposite the Cancer/Leo pair, Aquarius and Capricorn. Thus Mercury is in its face when it is semisextile to either the Sun or Moon in the chart at hand. Venus is in its face when it is sextile to either luminary, Mars when it is square, Jupiter when it is trine, and Saturn when it is inconjunct or quincunx. Ptolemy, discussd "the quality of the soul" in Tetrabiblos III.13. Al-Biruni accepts the faces "according to the agreement of the Persians and Greeks." His system is that of decanate rulerships using the Chaldean order. William Lilly, who used the term decanate synonymously with face, considered face the weakest form of essential dignity. The system he uses employs the Chaldean order of the planets, as described above. Alan Leo used face as a synonym for pentade. Simmonite used the term facet, but meant a five-degree section of the zodiac.