Saylor.org's Ancient Civilizations of the World/Medieval Society and Culture
In this section, we will examine the social hierarchies and culture that emerged from the Medieval Era. Central to this topic is an understanding to the medieval philosophical/religious conception of how the universe was ordered.
The Great Chain of Being
One of the most important ideas that governed medieval society was that of the "Great Chain of Being". The Great Chain of being held that all life (as medievals thought of it, although you will see some things in the chain were not 'alive' according to modern science) in the world was structured in an elaborate hierarchy of authority. At the top ruled God followed by the different classes of angels, demons (fallen/renegade angels), stars, the moon, kings, princes, nobles, men, wild animals, domesticated animals, trees, other plants, precious stones, precious metals, and other minerals.
God, and beneath him, the angels, both existing wholly in spirit form, sit at the top of the chain. Earthly flesh is fallible and ever-changing: mutable. Spirit, however, is unchanging and permanent. This sense of permanence is crucial to understanding this conception of reality. It is generally impossible to change the position of an object in the hierarchy. (One exception might be in the realm of alchemy, where alchemists attempted to transmute base elements, such as lead, into higher elements, either silver, or, more often, gold—- the highest element.)
In the natural order, earth (rock) is at the bottom of the chain: this element possesses only the attribute of existence. Each link succeeding upward contains the positive attributes of the previous link and adds (at least) one other. Rocks, as above, possess only existence; the next link up, plants, possess life and existence. Animals add not only motion, but appetite as well.
Man is both mortal flesh, as those below him, and also spirit as those above. In this dichotomy, the struggle between flesh and spirit becomes a moral one. The way of the spirit is higher, more noble; it brings one closer to God. The desires of the flesh move one away from God. The Christian fall of Lucifer is thought of as especially terrible, as angels are wholly spirit, yet Lucifer defied God, the ultimate perfection.
"The Great Chain of Being" (Wikipedia) http://en.wikipedia.org/wiki/Great_chain_of_being