Monday, August 02, 2010

Della Rocca on the PSR

Yale’s Michael Della Rocca has a paper out in support of the principle of sufficient reason (PSR). Della Rocca, whose expertise is on the Rationalists, begins the paper with a humorous shtick about how he is writing the paper against his better instincts, since he knows how little credibility the PSR has in contemporary mainstream philosophy.  [UPDATE 4 August 2010: I neglected to tip hat to Sympoze.]

His strategy in the paper is to push the burden of proof back onto those who dismiss the PSR.

To begin, he points out that we all make common use of what he calls an “explicability argument”. This is an argument where “a certain state of affairs is said not to obtain simply because its obtaining would be inexplicable – a so-called brute fact.” One of Leibniz’ examples was that of a scale or balance: if we hang equal weights on each side, we infer that the balance will remain still. That is because there is no reason why one side should hang down; if one side were to hang down, it would be inexplicable.

Della Rocca goes on to give many examples of explicability arguments with an emphasis on their role in contemporary philosophical debates: e.g., arguments that, say, consciousness or modality is dependent on other features (if not, they would be inexplicable).

Now take the case of existence: what explains why the things that exist exist? Unlike the other examples, taking on this question makes a “global” commitment to the PSR.

Della Rocca notes you can certainly say explicability arguments are useful in some cases, but not in the case of existence. Presumably this is what the opponent of the PSR would say. But then, he says, he has a right to ask for a principled argument regarding where you draw the line between the appropriate usage and the full-blown PSR.

He doesn’t want to hear appeals to intuition. The embrace of explicability arguments elsewhere is enough to get one to take seriously the possibility that it should apply to the case of existence as well. So we want a positive reason for its inapplicability here.

Another strategy might be to point to bad consequences of embracing the PSR, such as the Van Inwagen/Bennett argument that it leads to necessitarianism. Della Rocca says even if this is correct it doesn’t suffice as a principled case against the applicability of explicability arguments in the case of existence (in other words, if the PSR does mean necessitarianism, then so be it).

Pointing to the apparently anti-PSR implications of quantum mechanics is similarly missing the point about needing an argument for where the line is drawn on using explicability arguments.

So, until a line is drawn in a principled and non-arbitrary way, Della Rocca argues the PSR is alive and well.

My take: Della Rocca does not discuss further how the implications of QM might be involved in this debate, but my first though is that this is where I would develop an argument about drawing the line. I might argue that existence and certain other problems closely tied to it (conscious experience) are unavoidably concerned with quantum mechanics. On the other hand, many other problems in the macroscopic world do not depend on the specifics of QM, and thus can legitimately make use the explicability argument.

I would note that even in the world of QM, a weaker cousin of the PSR can still be potentially used: the things in our world depend on (but are not completely explained by) something else.


Allen said...

It seems to me that PSR commits you to the existence of an infinite array of infinitely long explanatory "causal" chains.

First, there's just the historical causal chain of events that lead to today. If every event in this chain has a cause, which itself has a cause, and so on - then you have an infinite past.

But then (at a right angle to the first chain) what caused us to have this particular infinite past instead of some other? And what caused that cause? And what caused the cause of the cause? And so on, to infinity.

BUT then we need a third explanatory chain at a right angle to this second chain - since we can ask why we have *this* particular second infinite chain of causation and explanation instead of some other...and this chain also goes to infinity

And so we keep adding infinite chains to explain our infinite chains...and PSR will never let us stop.

The PSR seems to guarantee that there is no bottom line to reality.

And in fact, I think kind of leads to the idea that *everything* exists...somewhere in this infinity of infinite chains.

As for QM...again, it's like poker - the randomness of QM exists within a deterministic framework (assuming physicalism). Presumably something must enforce the particular probability distributions and the regular aspects that allow us to mathematize it and use it for predictive purposes.

Steve said...

And in fact, I think kind of leads to the idea that *everything* exists...

I agree, and the weaker version of the PSR I mentioned gets you there as well.

Regarding QM; I think I understand your sense that the specific formalisms aren't necessary but contingent and therefore we can ask "what'a the explanation for QM?".

I see this, and yet there is something about QM -- about its dual structure of possibility space and spontaneous measurement outcome -- that seems to me like a bit of metaphysical truth that unexpectedly dropped into the lap of 20th century physics.