For something to go from potential to actual, some other thing already actual must bring the something in question to actuality; this is known as the principle of causality. The idea that something potential could bring itself to act - pulling itself up by its metaphysical bootstraps - is necessarily impossible. An example showing this impossibility would be the incoherent statement, “I actualized my own existence”. If I caused (i.e., actualized) my own existence, that implies I existed before I caused my own existence since for me to cause my own existence presuppose I already exist, thus making a self-contradicting claim.
So, change exists; change is the actualization of a potential; and for something potential to be actual requires a cause (i.e. something actual). Now, there are two applications of the principle of causality in reality: one deals with a temporal, static line of events (a linear casual series) that traces causes back in time, without any need for the series to terminate in some fundamental, first cause; the second kind deals with any given moment in time, particularly the very present moment (a hierarchical causal series) that involves causal power being derived from some fundamental member, the primordial source of a given causal power. An example of a linear causal series is a father who begets a son, and that son, in turn, begets his own son, and so on. This series could theoretically go on to infinity; taken at face value, there is nothing in this example that necessitates a first, most fundamental cause through which all the other members in the series rely upon in order to actualize their potency. In the example used, the first son requires nothing from his father to beget his own son once the first son is begotten; after the first son is begotten the father is irrelevant to the son continuing to exist and using his own causal powers (i.e. actualities) to actualize the potential life of his own son.
The metaphysics is different in a hierarchical causal series. In a hierarchical causal series, a first cause is necessary for the other, secondary members of the series to have any causal efficacy because derivativeness is the key factor in how a secondary cause can have causal power at all. Consequently, a hierarchical causal series is not concerned with the past in explaining how a potency is actualized, but how any potency is actualized at any moment, including here and now, given the secondary cause must derive its actualization from a first cause. I will provide three examples of a hierarchical causal series:
- A stone’s potency to roll is actualized by a stick pushing it; however, the stick can only actualize this potency insofar as a moving hand actualizes the stick’s potency to move.