Monday, September 25, 2023

The Principles of Sufficient and Partial Reasons

I have argued that the causal account of metaphysical possibility implies the Principle of Sufficient Reason (see Section here). The argument was basically this: If p is contingently true but unexplained, then let q be the proposition that p is unexplained but true. Consider now a world w where p is false. In w, the proposition q will be possible (by the Brouwer axiom). So by the causal account of modality, something can start a chain of causes leading to q being true. Which, I claimed, is absurd, since that chain would lead both to p being true and to p being unexplained. But the chain would explain p, so we have absurdity.

But it isn’t absurd, or at least not immediately! For the chain need not explain p. It might only explain the aspects of p that do not obtain in w. For a concrete example, suppose that p is a conjunction of p1 and p2, and p1 is false in w but p2 is true. Then a chain that leads to p being true need not explain p2: it might only explain p1, and might leave p2 as is.

I think what my argument for the PSR establishes is a weaker conclusion than the PSR: the Principle of Partial Reason (PPR), that every contingent truth has a partial explanation.

I am pretty sure that PPR plus causal finitism implies PSR, and so the modality argument for PSR can be rescued, albeit at the cost of assuming causal finitism. And, intuitively, it would be weird if PPR were true but PSR were not.


Dominik Kowalski said...

David Oderberg made such an argument before as well. Without a finite beginning, no full explanation for any event can be given, since the event will always have an infinite of antecendents which can't be fully explained themselves. Thus a past infinity violates the PSR. Contrary to some of the paradoxes, this particular argument has definitely a greater intellectual pull and is more straightforward

I can't link the article, but it's in the volume on the Kalam argument edited by Craig and Copan

Don said...


As I understand it, whether infinite or finite the past isn't a full explanation for anything. I think that's central to the whole distinction (in Aquinas) between per accidens and per se causal series.

Walter Van den Acker said...


That all depends on whether "X is possible" counts as a reason for X. If that is true, then the proposotion q is impossible.
And it seems to me that "X is possible" at least partially explains X.

Dominik Kowalski said...

Please elaborate. If you have a finite series, then the explanatory horizon is limited. The more you go into the future, the bigger the explanation gets. But nonetheless, it will be finite.

In regards to a per se series, most, though not all, per se series have a corresponding per accidens series.

Take me writing this answer out of my own volition. I the person accidens series, it involves everything sinful the big bang, if the big bang is the temporal beginning with nothing before it, as well as the per se series of me existing and directing my will towards this reply. As far as I can see, this explanation is limited

Don said...

I didn't explain my thoughts well initially. If by "fully explained" you mean in reference to a finite number of temporal causes then, yeah, that's definitionally true of a finite past. But to presuppose that "fully" is linked with "finite" would be begging the question. In our temporally past-finite world, the explanation of me writing today involves everything prior to now (which traces back to the big bang in our temporally finite world). In a hypothetical temporally past-infinite word, the explanation of me writing today would also involve everything prior to now. (In either case the temporal causes don't fully explain why I continue to exist, here and now, so not "everything" is explained. But this is a side issue which I had confused initially with the main issue of presupposing that fullness of explanation requires a finite number of causes.)