Element
The four elements, fire, earth, air and water, group the twelve signs into four triplicities and describe the basic quality each sign works through.
Each element covers three signs at 120 degrees from one another, which is why planets in the same element form trines. In the classical framework the elements carry the qualities: fire is hot and dry, earth cold and dry, air hot and wet, water cold and wet.
Those same qualities are what temperament is computed from, which is where the elemental layer of a chart meets the humoral one.
Frequently asked
What does a missing element mean?
That the quality has no planet expressing it directly. Traditional practice looks to the chart ruler and the Ascendant before calling it absent.
Are elements the same as modalities?
No. Elements group signs by quality; modalities, cardinal, fixed and mutable, group them by how they move.