This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
A quality entry records one of the three modes, cardinal, fixed and mutable, that group the twelve zodiac signs by their role within each of the four seasons, cardinal signs opening a season, fixed signs sustaining it, and mutable signs closing it and easing into the next, a threefold classification William Lilly's own 1647 textbook sets out as standard working vocabulary for the astrology he practiced and taught.
An entry records which four signs a quality covers, Aries, Cancer, Libra and Capricorn for cardinal; Taurus, Leo, Scorpio and Aquarius for fixed; Gemini, Virgo, Sagittarius and Pisces for mutable, and the documented seasonal reasoning Lilly's own text gives for the grouping, since the classification tracks the sun's actual seasonal position rather than an arbitrary division of the zodiac into equal thirds.
Lilly's book is a working manual written for practicing astrologers of its own period, so an entry can draw on it for the documented traditional meaning and use of a quality, distinct from any modern psychological gloss added to that older vocabulary by later writers working after Lilly's own seventeenth century context.
An entry also records that Lilly treats the quality as one factor among several a working reading combines with a sign's element and a planet's own dignity, never as a complete verdict about a chart factor read on its own.