Editing The Canon of Medicine (section)

===Thesis II The Elements of Cosmology===
Avicenna's thesis on the elements of the cosmos is described by Gruner as "the foundation of the whole ''Canon''".<ref name=Bakhtiar />{{rp|39}} Avicenna insists here that a physician must assume the four elements that are described by natural philosophy,<ref name=Bakhtiar />{{rp|34}} although Avicenna makes it clear that he distinguishes between the "simple" element, not mixed with anything else, and what we actually experience as water or air, such as the sea or the atmosphere. The elements we experience are mixed with small amounts of other elements and are therefore not the pure elemental substances.<ref name=Bakhtiar />{{rp|202}} The "light" elements are fire and air, while the "heavy" are earth and water:

#'''The Earth:''' Avicenna upholds [[Aristotelianism|Aristotelian philosophy]] by describing Earth as an element that is [[geocentric]]. The Earth is at rest, and other things tend towards it because of its intrinsic weight. It is cold and dry.<ref name=Bakhtiar />{{rp|35}}
#'''The Water:''' Water is described as being exterior to the sphere of the Earth and interior to the sphere of the Air, because of its relative density. It is cold and moist. "Being moist, shapes can be readily fashioned (with it), and as easily lost (and resolved)."<ref name=Bakhtiar />{{rp|35}}
#'''The Air:''' The position of Air above Water and beneath Fire is "due to its relative lightness". It is "hot and moist", and its effect is to "rarefy" and make things "softer".<ref name=Bakhtiar />{{rp|36}}
#'''The (sphere of the) Fire:''' Fire is higher than the other elements, "for it reaches to the world of the heavens". It is hot and dry; it traverses the substance of the air, and subdues the coldness of the two heavy elements; "by this power it brings the elementary properties into harmony."<ref name=Bakhtiar />{{rp|37}}