But it is not that their progress would absolutely lead to...

But it is not that their progress would absolutely lead to perfection of the last function and be a new form or at least make no interference with it. Rather in many cases the attainment of a perfection appropriate to the last form requires the restriction of former perfections, just as having a great deal of foliage interferes with a tree's process of bearing sufficient fruit or being exceedingly fat prevents a hound from reaching its ideal perfection of speed in gamboling and running.

As a result, the true perfection of every being consists of a trait or traits which he can possess in tune with his last function. Other matters will be preferential perfection and the preliminary of perfection to the extent that they are useful for the attainment of a being's true (form of) perfection. The Chain of Perfections When we compare a tree with gravel or a heap of sand, we realize that the tree actually possesses especial capacities not found in stone and sand.

Despite the similarity in their atoms and molecules, effects are derived from the tree that cannot emerge from stone and sand. We will express this truth in this way that there is potential perfection in the tree which is the plant feature and the origin of all activities and of produce exclusive to plants.

In like manner, plants are potentially possessed of perfections which inanimate objects are incapable of attaining, just as the sapling of a fruit-bearing tree is apt to bear loads of sweet fruit while no such capacity exists in stone and wood. Evidently, by possessing the said function and faculty, the plant not only does not lose its physical qualities and natural powers but also uses them to promote its functions and to go through the path of its functions and the path of its development.

Consequently, one can reach the conclusion that to reach perfection, a plant reaps benefit from natural powers and, of course is in need of them but to the extent that it can use them to reach perfection. Likewise, an animal possesses vegetable qualities plus sense and voluntary movement which is a requisite of its animal state. In the same manner, it employs vegetable qualities to reach human perfection. It needs these qualities to the extent that they are beneficial for its animal development.

In like manner, man possesses natural, vegetable, and animal qualities plus powers which emanate from humanity. Man employs all subordinate powers at the service of his human development.