Kepler added the quintile and the related fivefold divisions to the classical five aspects in the Harmonices Mundi of 1619, arguing from the consonant musical ratios he believed corresponded to the regular polygons that geometry allows to be constructed, the pentagon among them, rather than from the sign-based logic of the older Ptolemaic scheme. Despite being among the best documented of the minor aspects in terms of who introduced it and when, the quintile was never given a dedicated codepoint of its own in the Unicode Standard; it is noted in chart work by the letter Q, by the digit five, or by a stylised mark that varies from one program or publisher to the next, unlike the sextile, semi-sextile, quincunx and sesqui-quadrate, which did receive purpose-built astrological glyphs.
Because five does not divide evenly into the twelve signs of the zodiac, a quintile always links two signs of unrelated element and mode, a geometric fact later commentators have read as part of why the aspect's effects are felt as individual talent rather than as a shared temperament between the bodies involved. Kepler himself was explicit that he was breaking with the older, sign-based way of judging which angles mattered, arguing in the Harmonices Mundi that the ear and the compass, not the twelve signs, ought to settle the question, a genuinely new principle for choosing aspects rather than simply a new angle added to an old list.