This entry is the first of a two-part series in which I will summarize and defend Maydole's formulation of the Modal Third Way (MTW). First, some definitions:
temporally contingent - if x possibly fails to exist at time t, x is temporally contingent
temporally necessary - if x exists at all times in world W, x is temporally necessary in W
explicable - explained in at least one possible world
Here is the first part of the proof:
1. Every temporally contingent thing possibly fails to exist at some time.
(1) is true by definition.
2. If all things fail to exist at some time, then it is possible that all things collectively fail to exist at some past time.
We may grant that there was never a time in this world in which there didn't exist at least one temporally contingent thing. However, (2) is much less ambitious. Even the most ardent skeptic will agree that there is a possible world in which nothing existed in the past. (1) actually implies (2).
3. It is necessarily the case that possible truths are explicable.
Many of us (myself included) are already committed to the view that everything that exists has an explanation of its existence. However, some may not be convinced that this is so. Well, lucky for us, we can significantly weaken our principle and still end up with a good argument! Let's say that a brick just pops into existence uncaused and unexplained. To borrow Maydole's expression, it is "well nigh absurd" to assume that there is no possible world in which the brick's existence has an explanation. Such a conclusion would require that we prove a universal negative, and I doubt anyone is up to such a daunting task.
4. It is necessarily the case that something is explicable only if there was never a time when nothing existed.
Imagine that at some point in the past, nothing existed. Would anything exist right now? Surely not, but I'm sure we can find somebody who thinks so. "Out of nothing comes nothing," still seems much more plausible than its negation. What this implies for us is that if nothing existed at some past time, then nothing would exist right now, in which case nothing is currently explicable. But, we already saw in premise (3) that there are explicable things, which means that the contradictory of (4) is false, implying that (4) is true. Something had to have always existed, but no temporally contingent thing meets the qualification of necessity. Therefore, we have a link from these premises to:
5. If there was never a time when nothing existed, then a temporally necessary thing exists.
6. Therefore, something temporally necessary exists.