How does Michael Della Rocca defend strong rationalism and the Principle of Sufficient Reason in his reading of Spinoza, and what is its impact on the discussion of necessary existence?

This question touches the heart of contemporary debate about the Principle of Sufficient Reason (PSR) and its relationship to arguments for God's existence. Michael Della Rocca, in his radical reading of Spinoza, presents a defense of PSR in its strongest form, reviving philosophical discussions that were thought to have ended with the critique of Kant and Hume. The impact on the question of necessary existence is profound and multifaceted.

Inadequate Responses to Avoid

From some defenders of theism:

"Della Rocca proves God's existence with PSR." Wrong simplification. Della Rocca defends Spinoza who does not distinguish between God and nature (Deus sive Natura). Using his defense of PSR to prove a personal transcendent God ignores the essential Spinozan context. Della Rocca himself declares that strong PSR leads to "necessitarianism" which conflicts with traditional theism.

"PSR directly proves necessary existence." Logical leap. Even if we accept PSR in its strong form, the transition from "everything has a sufficient reason" to "there exists a necessary being" requires additional argumentative steps. Della Rocca himself focuses on the logical necessity of the world as a whole, not on the existence of a transcendent being.

"Criticism of PSR equals atheism." Arbitrary connection. Many theistic philosophers (van Inwagen, Pruss in a later stage) reject strong PSR while maintaining their faith. Rejecting PSR does not mean rejecting God's existence, but rejecting a particular way of proving it.

From some critics:

"Della Rocca is merely a historian of philosophy." Unfair reduction. True, Della Rocca specializes in the history of modern philosophy, but his defense of PSR in works like "PSR" (2010) and "The Parmenidean Ascent" (2020) are independent philosophical arguments, not mere historical interpretations.

"PSR has been definitively refuted since Kant." Ignoring contemporary discussion. Despite Kant's strong critique, PSR has returned forcefully in contemporary analytic philosophy. Alexander Pruss and Timothy O'Connor and others have offered new formulations that avoid some of Kant's criticism. Della Rocca is part of this return.

"Modern logic has invalidated PSR." A claim requiring verification. Modern logic does not "invalidate" PSR but clarifies its consequences. For example, modal logic shows the difference between weak and strong PSR, but it does not settle the metaphysical question.

Why These Responses Are Inadequate

They fail to realize that Della Rocca's defense of PSR has three layers: (1) historical interpretive regarding Spinoza, (2) independent argumentative for the principle, (3) exploratory of the consequences of accepting or rejecting it. Mixing these layers leads to misunderstanding his position.

Structure of Della Rocca's Defense

The Argument from Conceptual Clarity. In "PSR" (2010), Della Rocca argues that rejecting PSR leads to conceptual arbitrariness. If we accept that some facts have explanations and others do not, where do we draw the line? Why do we demand an explanation for a falling stone and not for the existence of the universe? Any dividing line will be arbitrary. The only coherent solution: either accept PSR completely or reject the principle of explanation entirely. Since rejecting explanation entirely destroys science and philosophy, we must accept PSR.

The Argument from Philosophical Practice. Della Rocca observes that philosophers who reject PSR theoretically apply it practically. When they argue against a position, they demand explanations and reject "brute facts" in other contexts. This pragmatic contradiction reveals that PSR is a principle that cannot actually be abandoned.

Radical Reading of Spinoza. In "Spinoza" (2008) and "The Parmenidean Ascent," Della Rocca reads Spinoza as a philosopher who takes PSR to its ultimate logical consequences:
- Everything has a sufficient reason
- A sufficient reason makes the caused thing necessary
- Therefore everything is necessary (necessitarianism)
- There is no real distinction between the possible and the necessary
- The entire world is logically necessary

This reading makes Spinoza more radical than usually thought, and connects PSR to absolute necessity.

Impact on the Question of Necessary Existence

Revival of Serious Discussion. Before Della Rocca, PSR was mostly discussed as a historical matter. His contemporary defense forced philosophers to take the principle seriously again. Even rejecters (like Peter van Inwagen) had to develop more sophisticated responses.

The Problem of Necessitarianism. If PSR is correct in the form Della Rocca defends, then everything is necessary. This poses a problem for traditional theism which affirms:
- Divine free will
- Possibility of alternative worlds
- Contingency of creation

Theists who want to use PSR (like early Pruss) face a dilemma: either accept necessitarianism (and lose divine freedom) or weaken PSR (and lose its demonstrative power).

The Challenge of "Brute Facts." Della Rocca makes accepting brute facts (facts without explanation) intellectually harder. But some theists (like Swinburne) rely on certain brute facts (e.g., God's own existence). Della Rocca's defense pressures them to justify why some brute facts are acceptable and others are not.

Reformulation of Cosmological Arguments. Contemporary discussion of cosmological arguments has been strongly influenced. Philosophers have become more careful in using PSR:
- Some (later Pruss) developed weak versions of PSR that avoid necessitarianism
- Some (Koons) used causal principles weaker than complete PSR
- Some (Rasmussen) developed arguments that do not depend directly on PSR

Counter-Criticism of Della Rocca

van Inwagen's Critique. In "Metaphysics" and "The Problem of Evil," van Inwagen argues that PSR leads to unacceptable results. If everything has a sufficient reason, then my actions have a sufficient reason, so I am not free. Freedom requires the possibility of brute facts (my free actions). Della Rocca accepts this result and rejects libertarian freedom, but many see this as a reductio ad absurdum against PSR.

Later Pruss's Critique. In his recent works, Pruss developed a precise critique: strong PSR conflicts with modern set theory. For example, there cannot be a sufficient reason for why the set of all sets does not exist (because any explanation would refer to a set, thus presupposing what we want to explain). This points to limits of PSR.

Bennett's Critique. In "A Philosophical Guide to Conditionals," Karen Bennett argues that Della Rocca's defense confuses levels of explanation. Demanding explanation for natural phenomena does not mean demanding explanation for every logical or mathematical truth. Distinguishing between types of facts is justified and not arbitrary.

Current Discussion Positions (2020-2024)

The "Modified PSR" Stream. Philosophers like Pruss and Koons are developing versions of PSR that retain sufficient explanatory power for cosmological arguments without falling into necessitarianism. For example, "every contingent fact has an explanation" instead of "every fact has an explanation."

The "Neo-Spinozan" Stream. Those influenced by Della Rocca (like Melamed and Lin) are exploring the possibility of accepting necessitarianism. They argue that the consequences are not as catastrophic as commonly thought, and that freedom can be understood compatibilistically.

The "Alternative Explanatory" Stream. Philosophers like Lange and Dasgupta are developing theories of explanation that do not depend on traditional PSR. They distinguish between types of explanation (causal, grounding, mathematical) and argue that each type has its own criteria.

Impact on the Ontological Argument

A striking paradox: Della Rocca's defense of PSR both strengthens and weakens the ontological argument simultaneously:

Strengthening: If PSR is correct, then the existence of a necessary being (God) becomes necessary to explain reality. The modal ontological argument gains strength because rejecting the existence of the necessary becomes a rejection of PSR.

Weakening: But if everything is necessary (necessitarianism), then the distinction between necessary and possible collapses. The traditional ontological argument depends on this distinction. In Spinoza/Della Rocca's world, "necessary existence" becomes an empty concept because there is no alternative.

Where We Stand in This Discussion Today

Between 2020 and 2025, the discussion crystallized around three main axes. First, Della Rocca's "The Parmenidean Ascent" (2020) provoked widespread responses, as he pushed PSR to its ultimate consequences even denying basic metaphysical distinctions (between substance and accident, between cause and effect), making many sympathizers with modified PSR retreat from supporting its strong form. Second, more moderate alternative formulations developed: Pruss and Koons continued developing PSR restricted to contingent facts, and Rasmussen offered arguments for necessary existence that do not depend directly on PSR but on lighter causal principles. Third, a post-Spinozan direction emerged (Melamed 2021, Lin 2023) exploring the possibility of adapting necessitarianism so it does not eliminate every legitimate distinction. Today's scene reveals that the debate has not been settled: strong PSR possesses considerable philosophical power, but its consequences remain costly for all parties—theists and naturalists alike.

From the Perspective of Rational Preponderance (rajḥān ʿaqlī)

Della Rocca's discussion reveals an epistemological structure that the method of rational preponderance deals with consciously:
─ The Principle of Sufficient Reason is neither demonstrative certainty nor intellectual illusion, but a principle with high rational plausibility strengthened by observing the regularity of explanation in sciences and philosophy.
─ The necessitarian consequences of its strong form do not invalidate it, but they call for modifying its formulation to preserve its explanatory power without committing to eliminating contingency and freedom.
─ Rational preponderance integrates PSR within a broader network of evidence: cosmological arguments, fine-tuning phenomena, moral intuition, and religious experience. PSR is not treated as an independent proof that settles the matter, but as a cumulative thread added to others.
─ The most rationally preponderant position is that a modified form of PSR (restricted to contingent facts) remains a legitimate tool in arguing for necessary existence, provided it is not burdened with more than it can bear. This aligns with the spirit of the cumulative method on which the database is based.