In an astrology without degrees, what is it that attracts one planet to another?
Obviously, it is the nature of the planet itself -and the sign or element it is in, plus a certain amount of free will or maturity on the part of the native(s) involved.
Fire and air planets will naturally gravitate towards one another as will earth and water. But what if that fire or air planet is in an earth or water sign?
A good knowledge of planetary ruler ships (dignities) and sign/planet harmony (synastry) is needed to tackle this subject.
Basically, masculine planets and signs (Fire and Air) get along well with one another as do feminine (Earth or Water) planets and signs. This differentiation between masculine and feminine (or positive and negative/extrovert and introvert/etc.) is the most BASIC and IMPORTANT divisor and indicator of compatibility or affinity in astrology. Everything else is an extension of it. Next in importance are the elements, modes, and polarities, and the individual signs or planets themselves. The chart below illustrates this.
Mars or Aries, for example, gets along best with itself, followed by the other two fire principles, and lastly the Air element. Of the air element, Earth/Libra is the most intimate because of the similarity of mode (both are cardinal). Fire does not get along with either the Earth element (which it finds too strong) or the water element (which it finds too weak).
Air is equal or complementary to fire but is superior or dominating to Earth and inferior or subordinate to Water. Earth and Water are equal or complementary to each other but incompatible to either fire or air.
Both the masculine and feminine genders are conflicting towards one another but equal in strength and this must be so in order to preserve balance in the universe.