Philosophers have perhaps more often assumed the Principle of Sufficient Reason than argued for it. Furthermore, this assumption has, in recent years, fallen out of favor due to the PSR’s allegedly unacceptable consequences. Recently, however, the PSR has been defended by Alexander Pruss and Michael Della Rocca. Pruss and Della Rocca both argue that (a version of) the PSR is a presupposition of reason. Pruss defends a version of the PSR restricted to contingent truths and consistent with libertarian free will and indeterminism is physics as a presupposition of our scientific and ‘commonsense’ explanatory practices. Della Rocca argues that the metaphysicians who deny the PSR implicitly make use of an unrestricted PSR, applying even to necessary truths, in other metaphysical arguments. Both arguments depend crucially on the claim that there is no weaker principle which is non-ad-hoc and justifies the relevant practices. In her contribution to The Puzzle of Existence, Shieva Kleinschmidt argues that both defenses fail.
Kleinschmidt’s general strategy is to outline contrasting cases – those in which admitting in-principle inexplicability seems to be an option, and those in which it does not – and argue that a non-ad-hoc descriptive account of this distinction can indeed be given.
Kleinschmidt’s primary focus is on Della Rocca, but compared to Pruss Della Rocca gives weaker support to a stronger conclusion. Della Rocca argues that if the unrestricted PSR is not true, then we cannot justifiably rule out certain metaphysical positions which we find intuitively implausible. However, not everyone finds the ‘brutal’ or ‘primitivist’ positions unpalatable in the way Della Rocca supposes (see Markosian). Furthermore, it would not be the end of the world if we were forced to conclude that many of the epistemic practices of analytic metaphysicians are in fact unjustified. Pruss, on the other hand, argues from commonsense and scientific explanatory practices. He asks, for instance, why it is that, when investigating a plane crash, no one takes seriously the hypothesis that the plane crashed for no reason at all. A position that undermined this kind of ordinary, everyday explanatory practice would be in much bigger trouble than a position that said analytic metaphysicians were out to lunch.
Now, Kleinschmidt does talk about the kind of everyday cases with which Pruss is concerned: “For instance,” she writes,
suppose we find small blue handprints along the wall, and we notice that the blue frosting is gone from its bowl and some is on the hands, face, and torso of a nearby five-year-old. When wondering what happened, we will not be tempted even for a moment by the alternative the child wishes to bring to our attention, namely, that the handprints are on the wall for no reason, that they are simply there (p. 67).
Again, someone who was forced to deny that our ordinary process of explaining the handprints was well-justified would be in much bigger trouble than someone who thought our metaphysical reasoning defective. Perhaps the reason for this is that Kleinschmidt herself belongs to the group of metaphysicians targeted by Della Rocca’s argument.
Della Rocca complains that these metaphysicians use the PSR when it suits them and ignore it the rest of the time. Kleinschmidt, however, thinks that this alleged inconsistency shows that Della Rocca has misunderstood the methodology employed by these metaphysicians, for there are indeed cases where (at least some of) these metaphysicians are willing to accept unexplained (and unexplainable) facts (whether necessary or contingent). These hypotheses are not ‘off the table’ in the way the hypothesis that the blue frosting is on the wall for no reason is off the table. In particular, Kleinschmidt describes in detail two contrasting cases: in standard fission cases, the view that it is simply a brute fact that either Lefty or Righty is identical with the pre-fission individual is rarely taken seriously, but in the Problem of the Many, especially as applied to human bodies, brute fact views have been more popular.
This, however, does not get to the bottom of things, for the common core of the arguments of Pruss and Della Rocca is the contention that no weaker principle than the PSR will justify our practice of treating these hypotheses as off the table in the cases where we do so. In other words, if we reject the PSR, then we ought to take the hypothesis that the blue handprints are on the wall for no reason seriously, but surely we ought not to take that hypothesis seriously, so we’d better accept the PSR.
It is only in the last three pages of her chapter that Kleinschmidt addresses this contention directly. She proposes that the claim that explanatory power is a truth-tracking theoretical virtue is sufficiently strong to account for our explanatory practices. “So, for instance, in the handprint case, we reject the theory that the handprints simply appeared for no reason, because we can see how some explanations might go, and some of the explanations are such that endorsing them won’t have disastrous consequences” (77). This, she argues, explains our explanatory practices: we take explanatory power to be a very important virtue in theory choice, so that we do not accept theories that render certain phenomena inexplicable unless we are backed into a corner.
As Kleinschmidt recognizes, this is really only the beginning of a response to Pruss and Della Rocca, for the core problem is not one of description but one of justification. Della Rocca, for instance, explicitly admits that metaphysicians are not consistent in rejecting unexplainables; this is precisely his complaint. He says that this inconsistent practice cannot be justified. Kleinschmidt recognizes this problem, but all she has to say about it is that there is considerable difficulty, as well, regarding the other features (e.g., parsimony) we take to be truth-tracking theoretical virtues.
Insofar as Kleinschmidt has helped to make clearer what our actual explanatory practices are, and shown that a descriptive account need not be radically disunified and ad hoc, this is progress. But the fact is, it is not really an answer to the Pruss-Della Rocca argument for, unless the treatment of explanatory power as a truth-tracking theoretical virtue can itself be justified, no method of justifying our explanatory practices in the absence of the PSR has been made to appear. On the other hand, perhaps Kleinschmidt should be regarded as having shown that those who continue to be untroubled scientific and/or ontological realists despite recognizing the difficulties involved in explaining why the features we regard as theoretical virtues should be regarded as truth-tracking might as well continue to be untroubled deniers of the PSR despite recognizing the difficulties raised by the Pruss-Della Rocca argument, for those difficulties are, essentially, the same. On the other hand, the reasonableness of this untroubled attitude could certainly be called into question.
Finally, it should be noted that Kleinschmidt’s formulations of the virtue of explanatory power are quite strong. She says we are willing to accept unexplainable propositions only when the consequences of refusing to do so are ‘disastrous.’ Now, unless one thinks either (a) that positing a necessary being is itself disastrous, or (b) that contingent facts cannot be explained in terms of a necessary being (i.e. that the modal collapse problem cannot be solved), this principle will still be strong enough to support the argument from contingency for the existence of a necessary being. (Personally, I think (a) is silly but (b) presents a deep and tangled problem.) In short, it seems likely that, even if we accept Kleinschmidt’s conclusion, we can still overcome the parsimony worries I discussed last time.
(Cross-posted at blog.kennypearce.net.)