How do critics of the Principle of Sufficient Reason (Van Inwagen, Bennett) respond to supporters, and do their responses beg the question?

The debate over the Principle of Sufficient Reason (PSR) represents one of the deepest disagreements in contemporary metaphysics. Peter van Inwagen and Jonathan Bennett have offered influential criticisms of the principle, while philosophers like Alexander Pruss and Timothy O'Connor have defended it. Understanding this debate is essential for evaluating the Leibnizian argument and other arguments that rely on PSR.

Inadequate Responses to Avoid

From some PSR defenders:

"Critics of PSR contradict themselves because they demand reasons for rejecting the principle." This confuses different levels. One can demand epistemic reasons for adopting a position without committing to the claim that every truth has a metaphysical reason. Van Inwagen is clear about this distinction: we need reasons for belief, but not every truth needs a metaphysical reason for being true.

"Rejecting PSR leads to comprehensive epistemic nihilism." This is an exaggeration. Critics of PSR do not reject all forms of explanation, but rather reject the claim that everything has a sufficient explanation. One can accept that most things have explanations without committing to the absolute universality of the principle.

From some PSR critics:

"PSR inevitably leads to absolute necessitarianism, which is absurd." This is an oversimplification. While van Inwagen developed the "proxy argument" to prove this, defenders like Pruss have offered revised formulations that avoid this conclusion. The claim that all formulations of PSR lead to absolute necessitarianism ignores recent developments.

"The existence of brute facts is self-evident and needs no proof." This is a dogmatic position. Even if we accept the possibility of brute facts, this does not mean they actually exist or that their existence is self-evident. The debate requires arguments, not mere declarations.

Why These Responses Are Inadequate

The common problem in these responses is the misleading simplification of a complex technical debate. The real debate concerns: What is the precise formulation of PSR? What are its logical consequences? And can the formulation be modified to avoid problems without losing explanatory power?

Van Inwagen's Criticism: The Proxy Argument

Van Inwagen presented in 1983 what is known as the "proxy argument" against PSR:

1. Assume PSR is correct: for every truth p, there is a sufficient explanation why p and not ~p.
2. Take the Big Conjunctive Fact (BCF): the conjunction of all possible truths.
3. According to PSR, BCF must have an explanation.
4. But any explanation of BCF must be part of BCF itself (since it is a truth).
5. Therefore BCF explains itself.
6. But complete self-explanation means that BCF is necessary.
7. Therefore every partial truth in BCF is also necessary.
8. This means absolute necessitarianism: everything that happened had to happen.

Strength: The argument reveals a real tension between PSR and contingency. If everything has a sufficient explanation, it seems that contingency vanishes.

Bennett's Criticism: The Problem of Arbitrary Stopping

Jonathan Bennett focused on a different problem:

1. PSR defenders accept stopping at the "necessary being" without explaining why it is necessary.
2. But if we accept stopping there, why not accept stopping earlier?
3. The claim that "necessity needs no explanation" seems arbitrary.
4. Therefore PSR either applies to everything (including necessity itself) or it does not apply.

Strength: This reveals a tension in how PSR is applied: does it apply to necessary truths or only to contingent ones?

Defenders' Responses and Whether They Beg the Question

Pruss's Response to Van Inwagen:

Alexander Pruss developed several responses, most importantly distinguishing between types of PSR:

1. Weak-PSR: for every contingent truth, there is a possible explanation.
2. Restricted-PSR: for every contingent truth about contingent beings, there is an explanation.
3. Causal-PSR: for every event with a beginning, there is a cause.

Pruss argues that weaker formulations suffice for the cosmological argument but avoid modal collapse.

Does this beg the question? Partially. Pruss implicitly acknowledges the strength of van Inwagen's criticism of the strong formulation and retreats to weaker formulations. But the question remains: are the weaker formulations strong enough to support the required metaphysical arguments?

O'Connor and Others' Response to Bennett:

Defenders distinguish between:
- Contingent truths (need external explanation)
- Necessary truths (self-explained by their nature)

Necessity is not a "brute fact" but an analytical property: the necessary being is explained by its essence.

Does this beg the question? Yes and no. On one hand, the distinction between necessary and contingent is a legitimate metaphysical distinction. On the other hand, Bennett is right that this seems like an ad hoc modification of the principle: we apply PSR until we reach what we want, then we stop.

Critical Assessment: Who Begs the Question?

Both sides accuse the other of begging the question:

Critics say: Defenders presuppose that brute facts are impossible, then use this to prove PSR.

Defenders say: Critics presuppose that some things need no explanation, then use this to reject PSR.

The truth is that both are partially right. The debate at its roots concerns basic metaphysical intuitions:
- Is intelligibility a necessary feature of reality?
- Can there be truths with no explanation whatsoever?

These are questions that cannot be settled by logical proof alone, but require balancing different considerations.

Current State of the Debate

Today's debate is more sophisticated:

1. Pluralism about PSR: Most philosophers accept that there are multiple formulations, some stronger than others.

2. Local vs. Global PSR: Even critics of global PSR often accept local versions (e.g., physical events have causes).

3. Pragmatic Considerations: The debate has partly shifted from "Is PSR correct?" to "Which formulation of PSR is most useful?"

For Advanced Reading

─ Advanced level: Contemporary formulations of PSR and their relation to quantum mechanics
─ Advanced level: PSR and determinism: can they be reconciled?
─ Van Inwagen, An Essay on Free Will (1983), Ch. 6
─ Pruss & Rasmussen, Necessary Existence (2018)
─ Bennett, A Study of Spinoza's Ethics (1984)