 This conception of the human mind as fundamentally active is taken up again in Thomasius’ lone substantial contribution to metaphysics, the Essay on the Essence of Spirit, where Thomasius distinguishes spirit (Geist) from matter in virtue of its activity. While this would appear to result in a metaphysical dualism, Thomasius complicates things by endorsing a hierarchy of spirits, not just between the human being and God, but also a class of spirits responsible for various effects in bodies (such as heating and cooling). Yet, his further postulation of an “air and light spirit [ein Lufft- und Licht-Geist]” which fills the spaces between parts of matter, not to mention his apparent identification of space itself as “pure spirit” (Thomasius 1709: 60, 167–8) muddles the original, starkly dualistic picture.