Principle of sufficient reason¶
The philosophical principle that every contingent fact has a sufficient reason why it obtains rather than not.
Core Idea¶
The principle of sufficient reason (PSR) holds, in a common formulation, that every contingent fact has an adequate reason why it obtains rather than not. Existence of that reason is the claim; neither present human knowledge nor an efficient physical cause is required in every formulation. Leibniz's Monadology presents sufficient reason beside non-contradiction and expressly allows that reasons for true facts may be unknown to us. Necessary truths can have a ground in necessity without needing a contingent event cause.
The principle is therefore stronger than the habit of continuing to ask why, yet different from universal physical causation. Leibniz applied it in the Clarke correspondence to challenge absolute-space placement: if two placements were wholly equivalent, what could distinguish the actual choice? That is a philosophical application, not a physical measurement. A critic might admit brute contingent facts or dispute the proposed contrast. The principle organizes that dispute; it does not supply a completed causal explanation for each fact.
Scope of Application¶
These uses retain the explanatory demand while declaring its domain.
- Metaphysical explanation. Assess whether contingent facts may terminate in brute unexplained facts.
- Leibnizian argument. Test whether an alleged choice among equivalent alternatives has a differentiating ground.
- Philosophy of religion. Distinguish PSR premises in cosmological arguments from their further theological conclusions.
- Methodological caution. Separate a commitment to explanatory adequacy from a successful empirical causal account.
Clarity¶
For a contingent fact, ask why it obtains rather than a relevant alternative. PSR says an adequate reason exists, not that people know it. The nearest miss is the weaker practice of continuing to search for explanations without asserting universal existence. Universal efficient causation is a stronger variant, not the whole doctrine; a truly brute contingent fact would challenge the stated formulation.
Manages Complexity¶
The short maxim hides several independent choices: the domain of facts, the strength of 'sufficient,' the alternative explained, whether reasons are causes, and whether unknown reasons count. Keeping these choices visible explains why Leibniz's absolute-space argument and a modern brute-fact objection can disagree without simply using different words. The principle organizes a dispute; it does not settle every explanatory chain by itself.
Abstract Reasoning¶
- Declare whether the version quantifies over contingent facts, all truths, existents, or events.
- State the focal fact and a relevant alternative to be explained.
- Ask what would count as an adequate reason in the chosen explanatory mode.
- Distinguish no known reason from a claim that no sufficient reason exists.
- Test a proposed brute fact or symmetry case without treating a causal story as the only possible response.
Knowledge Transfer¶
PSR can be applied from a dispute about cosmic existence to Leibniz's absolute-space placement argument when the explanandum, contrast, and sufficiency standard are restated. The latter does not transfer its spatial symmetry premise to every event. Scientific causal investigation may be motivated by explanatory ambition, but its empirical success or failure does not automatically establish or refute the universal metaphysical thesis.
Relationships to Other Abstractions¶
Current abstraction Principle of sufficient reason Domain-specific
Parents (1) — more general patterns this builds on
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Principle of sufficient reason is a kind of Law (Universal Principle) Prime
Principle of sufficient reason is a strict kind of Law (Universal Principle): its frozen identity entails the parent's defining structure while adding domain-specific restrictions.
Children (1) — more specific cases that build on this
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Causal adequacy principle Domain-specific is a kind of, typical Principle of sufficient reason
Causal adequacy is Descartes' reality-quantified version of demanding a sufficient ground for an effect: the cause must contain enough reality to explain it.
Hierarchy path (1) — routes to 1 parentless root
- Principle of sufficient reason → Law (Universal Principle) → Invariance
Neighborhood in Abstraction Space¶
Principle of sufficient reason sits in a moderately populated region (48th percentile for distinctiveness): it has near-neighbors but no dense thicket of look-alikes.
Family — Unclustered & Miscellaneous (2551 abstractions)
Nearest neighbors
- Subverted Support — 0.89
- Hume's Fork — 0.89
- Trivial Objections — 0.86
- I'm Entitled to My Opinion — 0.86
- Moore's paradox — 0.85
Computed from structural-signature embeddings · 2026-10-08