We divide the 12 signs of the Zodiac in three groups of 4 Elements each
They are also called Triplicities as each consists of 3 signs i.e. Fire, Earth, Air and Water.
Each Elements consists of three signs of the Zodiac and they are:
Fire: Aries, Leo and Sagittarius
Earth: Taurus, Virgo and Captricorn
Air: Gemini, Libra and Aquarius
Water: Cancer, Scropio and Pisces
It is easy to understand how each planet in your horoscope affects you if you analyze it both in terms of its Element and Quality.
For example, Venus in a Water sign will always indicate a very sensitive nature in love matters whether it is in Cancer, Scorpio or Pisces. However, in terms of its Qualiity, Cancer is the most self-oriented (Cardinal), Scorpio the most loyal (Fixed) and Pisces the most changeable (Mutable).