## Wednesday, August 14, 2019

### The present doesn't ground the past

I will run an argument against the thesis that facts about the past are grounded in the present on the basis of the intuition that that would be a problematically backwards explanation.

Suppose for a reductio:

1. Necessarily, facts about the past are fully grounded in facts about the present.

1. Necessarily, if fact C is fully grounded in some facts, the Bs, and the Bs are fully causally explained by fact A, then fact A causally explains fact C.

As an illustration, suppose that the full causal explanation of why the Nobel committee gave the Nobel prize to Bob is that Alice persuaded them to. Bob’s being a Nobel prize winner is fully grounded in his being awarded the Nobel prize by the Nobel committee. So, Alice’s persuasion fully causally explains why Bob is the Nobel prize winner.

1. It is possible to have a Newtonian world such that:

1. All the facts about the world at any one time are fully causally explained by the complete state of the universe at any earlier time.

2. There are no temporally backwards causal explanations.

3. There are at least three times.

Now, consider such a Newtonian world, and let t1 < t2 < t3 be three times (by (3c)).

Suppose that t3 is now present. Let Ui be the fact that the complete state of the universe at time ti is (or will be or was) as it is (or will be or was). Then:

1. Fact U1 is fully grounded in some facts about the present. (By (1))

Call these facts the Bs.

1. The Bs are fully causally explained by U2. (As (3a) holds in our assumed world)

Therefore:

1. Fact U1 is fully causally explained by U2. (By (1))

2. So, there is backwards causal explanation. (By (6))

3. Contradiction! (By (7) and as (3b) holds in our assumed world)

I think we should reject (1), and either opt for eternalism or for Merricks’ version of presentism on which facts about the past are ungrounded.

Michael Gonzalez said...

Why would a Presentist accept (3c)? And what on Earth does (1) even mean?

Does (1) mean that the grounding for the truth of statements about the past must be the truth of statements about the present? Or is the view that the grounding for truth of statements about the past must be present truths?

Michael Gonzalez said...

I ask just because I don't see why anyone would accept my first statement of (1), and my second statement of it doesn't seem to have the bad effect you're pointing out (since, of course, all truths are present truths; including ones about the past).

Heath White said...

It might have been the case that the past existed but the present did not.

Alexander R Pruss said...

Michael:

The wording of 3c is a slip. Read it as: there were, are or will be at least three times.

My target is views that ground facts about the past from facts about the present, e.g., grounding facts about what happened yesterday in God's memories of these events, or in some "having been F" type of property.

Heath:

That's an interesting argument!

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