There are two conceptions of observable reality. One views the observable universe mechanistically, much as a clock initially designed and built by some initial event or cause or God which merely unwinds itself. The other, the Aristotelian, Thomistic or hylemorphic view is that observable reality is more like a “performed” event which is maintained in existence at the present moment like a musical piece.
The problem with the mechanistic view is that it completely fails to explain what sustains the “mechanism” of observable reality – the “clock,” if you like – in existence here and now. What is the nature of the underlying reality that keeps things in existence at each moment?
The “linear” view of causation arises from the mechanistic view of the universe, and so causation proceeds from the past through the present into the future, sequentially in a way that requires time as the measure of change. This view merely assumes the mechanism keeps itself in existence a se at each moment and makes no attempt to explain why that would be the case.
The “vertical” or hylemorphic view adds the idea that causation also needs to explain why things exist at each moment in the here and now – how contingent things are sustained in existence at each present moment. According to this view of causation what needs to be accounted for is the vertical causal structure that makes things exist now – why there now exists something rather than nothing. That kind of causation can simply be encompassed in the present moment, in the immediate now and is not time dependent.
We thus have the two theories of time: A Theory and B Theory.
Now the truth might require something of both. That means secondary causation utilizing a series of accidental causes through time from past into the present and the future might be an aspect of reality. That does not exclude the necessity of per se or essential causation where a separate or vertical causal order is necessary to keep things in existence right here and right now. That kind of causation would be immediate, keeping things in existence completely absent any kind of time structure because the present moment might, in fact, be open to eternity and timeless.
You might want to view or listen in on these two clips:
An explanation of the two theories of time…
A discussion of two of Edward Feser’s proofs for the existence of God that gets fairly deep into the difference between accidental and per se causation and why the contingency of things in the here and now does not sufficiently explain the existence of things here and now.