We find its opposite in the water element, as expressed in the pentagon. The five is the second figurative prime number. The qualities of water are cold and humid, as opposed to the hot and dry of fire. It correlates to our emotions. In the cosmos it is the world of formation.
Water represents life while fire represents light.
Water and fire are considered to be the basic elements while the other two elements are regarded to be interactions between the two primary elements. Water is desire to manifest that goes with all life. It is desire and formation. Fire is will to create. The air element is interaction between fire and water.