In astrology, there are four natural elements:
Water, Earth, Fire and Air.
Every form of life (mineral, vegetable, animal, human…) is supposed to be made up of four elements.
As far as Man is concerned, Air forms the basis of breathing, Water can be found in every bodily fluid (water, blood, urine, sweat, lymph…), Earth is the symbol of all solid parts: flesh, bones, teeth, tissues… Fire is what animates the soul and the mind; it is what forms emotions.
Three astrological signs are associated with each natural element. This is what is called triplicity (three signs that are compatible). In theory, each sign will be in harmony with the two other astrological signs belonging to the same element.