Among the most important of the continuities with the Classical period was the concept of the Great Chain of Being. Its major premise was that every existing thing in the universe had its "place" in a divinely planned hierarchical order, which was pictured as a chain vertically extended. ("Hierarchical" refers to an order based on a series of higher and lower, strictly ranked gradations.) An object's "place" depended on the relative proportion of "spirit" and "matter" it contained--the less "spirit" and the more "matter," the lower down it stood. At the bottom, for example, stood various types of inanimate objects, such as metals, stones, and the four elements (earth, water, air, fire). Higher up were various members of the vegetative class, like trees and flowers. Then came animals; then humans; and then angels. At the very top was God. Then within each of these large groups, there were other hierarchies. For example, among metals, gold was the noblest and stood highest; lead had less "spirit" and more matter and so stood lower. (Alchemy was based on the belief that lead could be changed to gold through an infusion of "spirit.") The various species of plants, animals, humans, and angels were similarly ranked from low to high within their respective segments. Finally, it was believed that between the segments themselves, there was continuity (shellfish were lowest among animals and shaded into the vegetative class, for example, because without locomotion, they most resembled plants).