Introduction by Dimitri Gutas

Avicenna says: "It has already been proved in the previous sections that the elements from which corruptible things are generated are four and no more. And, when the one who considers this thinks about it, he will find that plants and animals, which are generated in earth, are nourished from earth and air and water, and their actuality is completed by heat arranging them. For earth makes the generated thing acquire [the power to] retain ... what is acquired when it is made and shaped. And water makes it easy for the generated thing to receive a shape. And the substance of water is preserved, since it is fluid, on account of being mixed with earth; and the substance of earth is preserved from diminution on account of being mixed with water. And air and fire keep [earth and water] from acting as elements and make them acquire the balance of a composite; and air opens up [the composite and makes for pores and pathways [for activities such as sensation and respiration], and fire digests, fuses, and aggregates."

Original Latin

How can four elements be the building blocks for all the substances (or rather, substantial composites) in the world? What does each of the four elements contribute? And once a composite has been produced, what makes it change?

A great physician and natural philosopher, Avicenna tried to answer all these questions. Key to his answers was the "Giver of Forms" a universal active intellect, which infuses the substantial form into the composite (mixt) when the elements are properly combined and disposed so that they have the right complexion for that form. The complexion depends on balance of elements and their qualities.

Within each mixt, to use the scholastic terminology, the forms of each element remain intact though their qualities are muted, so that mixt fire is not nearly as hot as elemental fire, for example.

Still, the qualities of each of the elements contributes to the characteristics of every substance, and here we are talking about animals, minerals and vegetables. Their watery element allows mixts the flexibility to receive a given shape, while the earthy element makes it possible for them to retain that shape. The heat which mixts get from both fire and air is the main active principle in arranging the elements and in the case of animals, in digesting food, though cold is also an active force.

Differences between composites depend largely on which element dominates in the mixt. Earth dominates in most of the substances we are familiar with, since they are located on earth, the terrestrial sphere. Heaviness is the chief characteristic of earthy composites, so they fall when placed in air and water. Fiery composites, by contrast, are very light and so they rise.

Most controversial about Avicenna's account was his claim that the elements in a composite preserve their fixed substantial forms, so that only their qualities of heat, coldness, dryness, and wetness are affected by their mixture. The heat of fire, for example is balanced by the coldness of earth and water.

Most scholastics believed Avicenna was wrong about this because if he were right, there would be many substantial forms in a substantial composite. Despite this disagreement, Avicenna's account was very important and deeply influenced some of the most original scholastic natural philosophers.