The cosmos was seen as a hierarchy or chain with matter at the lowest and God at the highest. Proportion, linked the essence or nature of each level of the hierarchy with its neighbor, and ultimately to God.
This way of understanding the proportion between individual things was also known as analogy. The relation of thing to thing is not a mere likeness, but instead the way in which contingency of being was articulated within the medieval hierarchy. A thing, such as material, was not understood to have the whole reason of its existence or being in itself, but through another, higher thing. This relation was understood as "causation".
Medieval causation was understood very differently from contemporary notions of causation. Efficient causes were seen to be conditioned and caused by one another within the medieval mind. Contemporary causation has no place for the effect to have influence on the cause, but in the case of understanding material proportionally within the medieval mind, we must see that material and form are connected and complement each other.
Material and form are proportional. The stone material in a medieval vault participates in the form of the vault. The uniqueness of the stone material determines the arch form, but cannot be understood outside of the arch form. Each, material and form, are conditioned and cause one another. This proportional understanding extended to include the entire cosmos.