Boston's Scollay Square is an example of a wholly past item. It existed, but it does not now exist. Boston's Copley Square, by contrast, existed and still exists: it has a past but it is not wholly past.
In an earlier exercise I gave an anti-presentist argument one of the premises of which is:
d) It is not the case that Scollay Square is [now] either merely possible or impossible: what passes away does not become merely possible or impossible.
The Ostrich objected:
I didn’t follow the assumption (d) above. Scollay Square is impossible, having perished.
The question is this: When a thing that actually existed passes away and becomes wholly past, does it cease to be actual and become impossible? Can the passage of time affect an object's modal status?
I say No; the Ostrich says Yes. My No, however, will be nuanced by a distinction I shall introduce shortly.
I concede to the Ostrich that there is a sense in which Scollay Square, that very item, is now impossible: it cannot be restored to existence. (If you made a copy of it, the copy would not be it.) After the demolition was complete, there was nothing anyone could do to bring back that very item. In this respect the demolition of the famous square is like a person's loss of virginity. If you lose your virginity at time t, then there is nothing anyone can do after t to undo the loss. (Repairing a girl's hymen would not do the trick. Hymenoplasty is possible but it is not the same as restoration of virginity.)
Now there is no need to drag the Deity into this debate, but I will do it anyway just to throw the issue into relief. Not even God can restore a virgin or bring back Scollay Square (where many a sailor lost his virginity). This is because it is the very natures of time and existence that prevent the restoration. (Now please forget that I even mentioned God, and do not ask me any questions about divine omnipotence.)
Let's consider another example. Our patron Socrates was executed by the Athenian state. That event might not have occurred. That is, his execution was not metaphysically necessary. In the patois of 'possible worlds,' there are possible worlds in which Socrates is executed and possible worlds in which he is not. Therefore, his execution was metaphysically contingent and remains sub specie aeternitatis metaphysically contingent despite the fact that the execution cannot be undone. But if the execution cannot be undone and was impossibly undone from the moment of the event onward, then how can the execution be contingent? Is it not necessary? Obviously, we need to make a distinction.
Metaphysical versus Time-Bound Modalities
We have to make a distinction between metaphysical modalities and time-bound modalities. We can say that Socrates' execution, while metaphysically contingent, nevertheless enjoys necessitas per accidens and its undoing impossibilitas per accidens. Nothing hinges on this particular terminology, but there is a distinction to be made here.
Someone could say, and the Ostrich perhaps will say, that before Socrates came to be, he was merely possible, that when he came to be he became actual, and that after he passed away he became impossible. If this makes sense, then our man's modal status is time-dependent.
I think the following are logically consistent:
1. It is impossible that an actual being that no longer exists be restored to existence.
2. A metaphysically contingent being that exists in the sense that it existed, exists, or will exist retains its modal status when it passes away. Socrates exists in this disjunctive sense. When Socrates ceased to exist (assuming no immortal soul) he retained his modal status: actual but not necessary.
(1) is a concession to the Ostrich. But (2) is also true. I am inclined to accept a Growing Block theory of time: as time passes the 'block of reality' gets bigger and bigger. Everything that IS is actual, and everything that WAS is also actual. The past is not nothing: it is real.
Socrates is (in the disjunctive sense) an actual being. This may be the same as saying that he is tenselessly actual. His passing away does not affect his metaphysical modal status. He is no longer temporally present but he is nonetheless metaphysically actual.
Furthermore, he remains a contingent being after his passing. He does not become an impossible being.
So I think we can achieve a sort of irenic if not quite Hegelian synthesis. The Ostrich is speaking from the perspective of the present. (I suspect he is a presentist and I should like him come clean on this.) From the point of view of the present, the wholly past is now impossible in the sense that nothing ANYONE can do can restore the past or bring it back. I believe I have accommodated, with all due charity, the insight of the Ostrich.
But we also have the power to view things 'from above,' We are time-bound to be sure, but we are also "spectators of all time and existence" as Plato once taught us. Looking down upon this scene of flux and folly we can 'see' with the eye of the mind the tenseless modal relationships that obtain here below. These are not affected by the passage of time.
For example, no contingent being is impossible. Socrates is a contingent being. Ergo, Socrates is not impossible. He was not impossible before he became present; he was not impossible when he was present; and he is not impossible now when he is past. He is tenselessly contingent.
The stable view sub specie aeternitatis is just as valid as the view from one's shifting temporal location.
The question is this: When a thing that actually existed, or an event that actually occurred, passes away and becomes wholly past, does it cease to be actual and become impossible?
The Ostrich answers in the affirmative. I think this answer is sustainable only if presentism is true. Presentism, however, is hard even to formulate (nontrivially), let alone evaluate.
I must now demand of the Ostrich that he come clean and tell us whether he is indeed a presentist. If I am not mistaken most if not all of the medieval philosophers he studies are presentists; if so, he may be unaware that there are alternatives to ptesentism. It may just seem obvious to him when it ought not seem obvious to him.