Nature as the Principle of Change and Permanence
After criticizing the philosophers’ idea of ‘two consecutive phases’ in motion,[35] Sadra discusses briefly the problem of how changing things (mutaghayyir ) are related to an unchanging and permanent principle (th abit ). If every changing body is preceded by another changing body, this leads either to an endless chain or to a change in the First Principle, which we have already ruled out as impossible.Sadra eliminates this objection by saying that the continuous renewal of material bodies is their essential attribute, not a quality added to them from outside. When a corporeal thing moves towards its ‘existential realization’, viz., actualizes its potentialities by going through various forms and states of being, such as emerging from potentiality to actuality or moving from one location to another, it possesses its immediate cause of motion/change in itself, and does not need an extra ‘cause’. Even when an extraneous stimulator is required for a thing to move externally, this is made possible only by having recourse to the nature inherent in things.
The gist of the foregoing arguments is that every natural body carries the principles of change and permanence in itself simultaneously. Nature, for example, remains an enduring property in physical bodies while its very reality is change. By the same token, there are certain things whose actuality is their potentiality such as thehyle , or whose plurality is their unity such as the numbers, or whose unity is their plurality such as the material body with its components as a whole.[36] Thus, everything has a dual structure in its essential constitution. In this respect, nature andhyle appear to be the two basic points of connection between the changing and the unchanging.
Considered in its aspect of permanence, nature is directly connected to the permanent principle. When considered in regard to its aspect of change and renewal, however, it is connected to the renewal of material bodies and the origination of created beings. In a similar way, thehyle serves as the connection point between the potentiality and actuality of contingent beings. It is thus concluded that “these two substances (i.e., nature andhyle ) are simply means of origination and corruption of material bodies, and through them a relation is established between the eternal (al-qadi m ) and the created (al- hadith )’.[37]