Full context:   Two incompatible elemental systems competed in Hellenistic astrological circles, both of them attached to the seasonal Zodiac: the "Egyptian" system, also used by the Stoics, which is symbolic (FIRE-WARM, WATER-WET,AIR-COLD, EARTH-DRY), and the "Mesopotamian" system, also Aristotelian (neo-Hippocratic), which is physical (AIR-WET, FIRE-WARM, EARTH-DRY, WATER-COLD). The Stoic organization seems to me better in alignment with the nature of elements that are no more than symbols. So we will keep the distribution of elements on the condition of understanding it as a symbolic paragon of the Tetrad. The Elements are symbols of the four states of matter (solid, liquid, gas, plasma), which is to say, they are material images of the Tetrad.