 The two non-material principles, spirit and soul, related to each other analogously. Soul, the principle of motion, aggregated atoms and thereby determined the identity of a body. Spirit—the spiritus popularized by Ficino—was the incorporeal medium through which soul connected with body. Soul accounted for the existence of fire. In its purest form, fire was the combination of water and light, which, as others, including Ficino, had explained, was the physical analogue of the intellectual soul governing all things (for soul and light, see further  Section 4). This explained why flame resembled water flashing in sunlight: in the former, soul predominated, in the latter, water. The Egyptians Hermes Trismegistus and Moses corroborated this idea. Both had understood fire to be essentially water (BOL I.1, 376; Genesis 1:6–7; Hermes Trismegistus, Pimander, I.5). Again, in Genesis 1:1–3 Moses had spoken of earth, the water (the “abyss”), spirit and light but ignored fire and air, precisely because they were not true elements. Similarly air was a derivative rather than, as conventionally believed, an element in its own right. Heat generated by fire vaporized water to produce the air of the kind that we breath, and this vaporous air merged seamlessly into the empty, dimensionless, space beyond the atmosphere surrounding a celestial body. This space was the aether, though not the aether of conventional cosmology. It was the continuum spread throughout the universe and through the corporeal things contained in it, binding them together—not unlike the Stoic pneuma interpreted as hexis—without, however, moving them. It was, in other words, spiritus, the motionless immaterial medium through which soul, the principle of motion, operated. As such, spiritus or aether was the container—non-terminated space—in which all things were located.