# Causal Principle ## Intro The **causal principle** is the metaphysical claim that things do not pop into existence without a cause. In its most defended modern form, it says: *whatever begins to exist has a cause*. This is the first premise of the [Kalam Cosmological Argument](/codex/kalam-cosmological-argument/), and it is the philosophical hinge on which much of natural theology turns. If everything that comes into being has a cause, and the universe came into being, then the universe has a cause. Deny the principle and the argument collapses; affirm it and the apologist is most of the way home. The principle has been formulated in several strengths. The **weak causal principle** (Kalam form) restricts the claim to things that begin to exist, leaving necessary beings (if any) outside its scope. The **strong causal principle** (the medieval *ex nihilo nihil fit*, *out of nothing, nothing comes*) is sometimes formulated more broadly. The **Principle of Sufficient Reason** (Leibniz) is stronger still: *everything that exists has a sufficient reason for its existence, either in another or in itself.* PSR entails the causal principle but goes further by demanding explanation even of necessary beings. The principle has classical roots in [Plato](/codex/plato/) (*Timaeus* 28a: *everything that becomes has a cause*), [Aristotle](/codex/aristotle/) (the four causes; nothing comes from nothing), [Augustine](/codex/augustine/), [Thomas Aquinas](/codex/thomas-aquinas/) (the Second Way), and the broader scholastic tradition. Its modern champion is [William Lane Craig](/codex/william-lane-craig/), whose *Kalam Cosmological Argument* (1979) revived and analytically sharpened the Islamic kalam tradition for contemporary philosophy of religion. Its contemporary deepening through PSR is the work of [Leibniz](/codex/leibniz/) and, in our own day, Alexander Pruss, Joshua Rasmussen, and Robert Koons. The principle is contested. David Hume denied that we have any rational warrant for the necessary connection between cause and effect; Lawrence Krauss and a small minority of physicists argue that quantum-vacuum fluctuations show particles can come from nothing; Graham Oppy and other contemporary atheists argue the principle is at best a contingent generalization, not a necessary metaphysical truth. The debate over the causal principle is therefore not a sideshow to the cosmological argument. It is the load-bearing dispute. ## In full The **causal principle** (CP) is the metaphysical thesis that the coming-into-being of any contingent entity requires an efficient cause adequate to produce it. The principle has several non-equivalent formulations: (1) **Kalam CP**, *whatever begins to exist has a cause* (Craig 1979), restricted to temporally-originating entities; (2) **strong CP**, *ex nihilo nihil fit*, nothing can come into being from absolute nothing, formulated as a universal metaphysical impossibility claim; (3) **Principle of Sufficient Reason** (PSR), *for every contingent being there is a sufficient reason for its existence*, which entails CP and extends it to all contingent existence, not only origination; (4) **causal PSR** (Pruss 2006), a restricted PSR claiming that every contingent fact has a causal explanation. The principle's modal status, its scope, the type of cause required (efficient vs. final, simultaneous vs. temporally prior, agent vs. event), and its epistemic warrant (a priori intuition, inductive generalization, transcendental presupposition) are all contested. The principle anchors the entire family of cosmological arguments ([Kalam Cosmological Argument](/codex/kalam-cosmological-argument/), [Contingency Argument](/codex/contingency-argument/), [Aquinas Five Ways](/codex/aquinas-five-ways/)) and is the central philosophical battleground between contemporary theists (Craig, Pruss, Rasmussen, Koons) and atheists (Hume, Mackie, Oppy, Krauss). ## Classical formulations ### Plato [Plato](/codex/plato/), *Timaeus* 28a: *"Everything that becomes or is created must of necessity be created by some cause, for without a cause nothing can be created."* This is one of the earliest explicit statements of the causal principle in Western philosophy. Plato applies it to argue that the cosmos, which "becomes," must have a Demiurge as its cause. ### Aristotle [Aristotle](/codex/aristotle/) develops the doctrine of the **four causes** in *Physics* II.3 and *Metaphysics* V.2: the **material** cause (what something is made of), the **formal** cause (its essence or pattern), the **efficient** cause (what brings it about), and the **final** cause (the end for which it exists). The causal principle in its modern Kalam form is restricted to efficient causation, but the Aristotelian framework provides the metaphysical resources for a richer account. Aristotle also affirms a version of *ex nihilo nihil fit* in *Physics* I.4, though his view of the cosmos as eternal means he does not deploy the principle as the moderns do. ### Augustine [Augustine](/codex/augustine/), *Confessions* XI and *City of God* XI.6, holds that God created time itself along with the world, dissolving the question *"what was God doing before creation?"* This is significant for the causal principle because it shifts the question from temporal antecedence (*what existed before X?*) to ontological dependence (*what does X depend on?*). The Augustinian framework anticipates Craig's modern handling of *"prior to time"* causation. ### Aquinas [Thomas Aquinas](/codex/thomas-aquinas/), *Summa Theologiae* I.2.3, the **Second Way**: *"In the world of sense we find there is an order of efficient causes. There is no case known, neither indeed is it possible, in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible."* Aquinas's argument runs on the impossibility of an infinite regress of *per se* (essentially-ordered) efficient causes, terminating in a first cause that all call God. Aquinas's *per se* / *per accidens* distinction is crucial: he does not (unlike Craig) hold that an infinite regress of temporally-ordered causes is impossible; he holds that an infinite regress of presently-sustaining causes is impossible. This distinction matters for the modern debate because Kalam (Craig) and Thomistic cosmological arguments (Feser, Oderberg) make different demands on the causal principle. ### Scholastic and rationalist tradition The scholastic axiom *ex nihilo nihil fit* ("out of nothing, nothing comes") was treated as a self-evident first principle from Parmenides forward. It was formalized in Suarez's *Disputationes Metaphysicae* and inherited by [Leibniz](/codex/leibniz/), who built it into the more comprehensive **Principle of Sufficient Reason**: *"nothing happens without a reason why it should be so rather than otherwise"* (*Monadology* §32, *Theodicy* §44). For Leibniz, PSR is the second of the two great principles of reasoning (alongside the principle of non-contradiction) and is the foundation of his cosmological argument. ## Modern Kalam formulation [William Lane Craig](/codex/william-lane-craig/), *The Kalam Cosmological Argument* (Macmillan 1979) and *Reasonable Faith* (Crossway, 3rd ed. 2008), revived the medieval Islamic kalam tradition (al-Ghazali, al-Kindi) for contemporary analytic philosophy. Craig's argument: 1. Whatever begins to exist has a cause. 2. The universe began to exist. 3. Therefore, the universe has a cause. Craig's formulation is deliberately **restricted**: it does not say *everything has a cause* (which would invite the *"then what caused God?"* rejoinder), only that *whatever begins to exist has a cause*. A necessary being (if any) does not begin to exist and so is exempt. This restriction is the key analytic move that distinguishes the modern Kalam from cruder formulations. Craig defends premise 1 on three grounds: - **Metaphysical intuition.** It is a bedrock intuition that things do not pop into being uncaused out of nothing. The intuition is stronger than any premise an opponent could marshal against it. Craig: *"to suggest that things could just pop into being uncaused out of nothing is to quit doing serious metaphysics and to resort to magic."* - **Inductive support.** Every case of beginning-to-exist we have ever observed has been caused. Universal experience confirms the principle. - **Theoretical role.** Science itself presupposes the principle. The methodology of empirical inquiry is to seek causes for events; if some events were genuinely uncaused, that methodology would be unjustified. Craig defends premise 2 with philosophical arguments (the impossibility of an actual infinite, the impossibility of forming an actual infinite by successive addition) and scientific arguments (Big Bang cosmology, the Borde-Guth-Vilenkin theorem). The conclusion is that the universe has a cause, which Craig then argues must be personal, timeless, spaceless, immaterial, and enormously powerful. ## The contested premise The causal principle is the **target** in nearly every serious attack on the Kalam argument. Premise 2 is also contested but is fought largely on scientific terrain (cosmological models). Premise 1 is fought on metaphysical terrain, and the dispute turns on six contemporary questions: - **Modal status**: Is CP a necessary metaphysical truth (true in every possible world), a contingent empirical generalization (true in this world but possibly false elsewhere), or a transcendental presupposition (something we must assume to make sense of experience)? - **Scope**: Does CP apply only to material events, or also to the coming-into-being of the universe itself? Critics (Smith, Oppy) argue Kalam illicitly extends an intra-universe principle to the universe-as-whole. - **Type of causation**: Does CP require an efficient cause, a sufficient reason, a ground, or all three? Different formulations have different defensive resources and different opposing objections. - **Temporal vs. simultaneous causation**: Does CP require the cause to be temporally prior to the effect? If so, what does it mean for God to cause the first moment of time? Craig defends a model of timeless causation; Aquinas a model of sustaining causation. Both move beyond the simple temporal-priority picture. - **Quantum exception**: Do quantum-mechanical events (radioactive decay, vacuum fluctuations) constitute uncaused beginnings-to-exist? If so, CP is empirically falsified. - **Possible-worlds counterexamples**: Can we coherently conceive of a possible world in which something begins to exist without a cause? If so, CP cannot be a necessary truth. ## Major objections ### Hume's denial of necessary causal connection [David Hume](/codex/david-hume/), *Enquiry Concerning Human Understanding* §IV and §VII, *A Treatise of Human Nature* I.3, argues that our idea of causation does not include any logically necessary connection between cause and effect. We observe constant conjunction (B always follows A) but never observe the necessary tie. The idea of causation is therefore a psychological projection (the mind's habit of expecting B after A), not a feature of objective reality. If Hume is right, the causal principle has at most contingent inductive support, not the necessary metaphysical status the cosmological argument needs. Hume goes further: in his *Dialogues Concerning Natural Religion*, he writes *"it is not absurd to suppose that something might come into existence without a cause."* This is the locus classicus of the modern objection. **Theist replies**: (a) Hume's analysis of causation is widely rejected even by non-theist contemporary philosophers (counterfactual, dispositional, and powers-based accounts of causation have replaced the Humean regularity view); (b) Hume's conceivability claim conflates *imaginability* with *metaphysical possibility*; (c) Hume himself elsewhere affirms the causal principle as a working assumption (Pruss 2006 catalogs Hume's many uses of CP in argument). ### Quantum-vacuum fluctuation A minority of physicists (Lawrence Krauss, Stephen Hawking in popular writing) argue that quantum mechanics shows particles can come into existence without cause. Virtual-particle pairs in the quantum vacuum, the spontaneous nucleation of universes from a vacuum state, and similar phenomena are taken to falsify CP empirically. **Theist replies**: - The quantum vacuum is **not nothing**. It is a sea of fluctuating energy governed by determinate physical laws. Virtual particles arise from this substrate, not from absolute nothing. Calling this *"a universe from nothing"* trades on equivocation: physicists' *"nothing"* is metaphysicians' *"something quite substantial."* David Albert's review of Krauss's *A Universe from Nothing* (*New York Times*, 2012) demolishes the conflation: *"the laws of relativistic quantum field theories do not constitute a 'something' from which 'nothing' could be derived."* - Quantum events have **probabilistic** rather than deterministic causes, but probabilistic causation is still causation. The causal principle is not the deterministic principle. - On interpretations of quantum mechanics (Bohmian, GRW, certain MWI variants) quantum events are fully causally determined. Craig devotes substantial attention to this objection in *Reasonable Faith* and his exchanges with Sean Carroll. ### Krauss's "A Universe from Nothing" Lawrence Krauss, *A Universe from Nothing* (Free Press 2012), argues that modern cosmology and quantum field theory can explain the origin of the universe without invoking a cause. The book has been widely criticized (by Albert, by Edward Feser, by William Lane Craig) for the equivocation noted above. Krauss in fact offers three distinct accounts of *"nothing"* (the quantum vacuum, the absence of space and time, the absence of laws), and slides between them. None of his accounts is the metaphysician's *nothing* that CP is concerned to deny things can come from. ### Possible-worlds counterexamples Graham Oppy, *Arguing about Gods* (Cambridge 2006), *The Best Argument against God* (Palgrave 2013), argues that we can coherently conceive of possible worlds in which the causal principle fails. If CP holds at most contingently, it cannot do the necessary work the cosmological argument asks of it. **Theist replies**: (a) Pruss (2006) and Koons (2008) argue that conceivability is a weak guide to possibility; (b) the burden of proof runs the other way (the theist need only show CP is *plausible*, not that no opponent can imagine its negation); (c) the same conceivability arguments would undermine the principle of non-contradiction, which Oppy presumably wants to keep. ### Mackie's challenge J. L. Mackie, *The Miracle of Theism* (Oxford 1982), grants the historical pedigree of CP but denies its rational warrant. Mackie's challenge: produce a non-circular, non-question-begging argument for CP that does not appeal to mere intuition or inductive generalization. He thinks no such argument exists, and so CP cannot do the work the cosmological argument requires. **Theist replies**: (a) Pruss's *Principle of Sufficient Reason* (2006) offers exactly such arguments, including modal arguments, self-defeat arguments against denying PSR, and pragmatic transcendental arguments; (b) intuition is not "mere" intuition when the intuition is universal, deeply held, and presupposed by every other inquiry; (c) the demand for non-circular argument applies symmetrically to denial of CP. ## Major defenses ### William Lane Craig [William Lane Craig](/codex/william-lane-craig/), *The Kalam Cosmological Argument* (Macmillan 1979); *Reasonable Faith* (Crossway, 3rd ed. 2008); *The Blackwell Companion to Natural Theology* (Wiley-Blackwell 2009, chapter co-authored with James Sinclair). The most extensive contemporary defense of the Kalam-form CP. Craig argues the principle is grounded in metaphysical intuition, universal inductive experience, and the methodological presuppositions of science. ### Alexander Pruss Alexander Pruss, *The Principle of Sufficient Reason: A Reassessment* (Cambridge 2006). The most thorough recent defense of PSR (and so, derivatively, of CP). Pruss surveys and answers the standard objections (van Inwagen's "modal collapse" argument, Hume, Mackie), offers positive arguments (self-defeat of PSR-denial, the necessity of explanation for inquiry), and develops a restricted causal PSR that avoids the most powerful objections. ### Joshua Rasmussen Joshua Rasmussen, *Necessary Existence* (Oxford 2017, with Alexander Pruss); *How Reason Can Lead to God* (IVP 2019). Develops a contemporary cosmological argument that runs on a contingent-explanation principle weaker than full PSR but strong enough to support theism. Rasmussen's strategy is to find the weakest principle that does the apologetic work, narrowing the dispute to a principle the atheist will find hard to deny. ### Robert Koons Robert Koons, *"A New Look at the Cosmological Argument"* (*American Philosophical Quarterly* 1997); *Realism Regained* (Oxford 2000). Defends a contemporary version of the cosmological argument grounded in a causal PSR. Koons's argument is notable for using the resources of contemporary formal mereology and modal logic. ### Edward Feser Edward Feser, *Aquinas* (Oneworld 2009); *Five Proofs of the Existence of God* (Ignatius 2017). Defends the Thomistic version of the causal principle (the *per se* essentially-ordered series, the act-potency framework, the real distinction between essence and existence) as superior to the Kalam version. Feser argues the Kalam debates over the beginning of the universe are a sideshow; the deep argument runs on the present-tense sustaining causation Aquinas was concerned with. ## Modal status The single most consequential question about CP is its **modal status**: is it necessary or contingent? - **Necessary metaphysical truth**: CP holds in every possible world. (Craig, Pruss, Koons, Feser.) On this view, CP is on par with the principle of non-contradiction. Denying it amounts to a category error or a failure to grasp what causation is. - **Contingent strong generalization**: CP is true in our world but logically could be otherwise. (Hume, Oppy, some Mackie passages.) On this view, CP is empirical and probabilistic, like the conservation of energy. Its truth in this world supports apologetic use only inductively. - **Transcendental presupposition**: CP is not a substantive claim about the world but a precondition of intelligible experience. (Kantian descendants; some readings of Strawson.) On this view, CP is necessary in the sense that we cannot coherently deny it while continuing to think or speak. - **Pragmatic posit**: CP is a methodological commitment of scientific inquiry. (Some pragmatists, instrumentalists.) On this view, CP is justified by its theoretical fruitfulness, not by metaphysical insight. The cosmological argument needs CP to be at least *more probable than its negation*. The stronger the modal status, the stronger the argument. ## Apologetic stakes The causal principle is the load-bearing premise of the entire cosmological tradition. It anchors: - The [Kalam Cosmological Argument](/codex/kalam-cosmological-argument/) (Craig's modern formulation). - The [Contingency Argument](/codex/contingency-argument/) (the Leibnizian formulation running on PSR). - The [Aquinas Five Ways](/codex/aquinas-five-ways/) (the First, Second, and Third Ways all deploy a version of CP). - Contemporary grounding-based cosmological arguments (Schaffer's priority-monist resources turned theistic by Rasmussen and others). If CP fails as a necessary metaphysical truth, the strongest forms of the cosmological argument fail with it; weaker forms (inductive, abductive, best-explanation) may survive. If CP holds, the apologist has the philosophical machinery to argue from the existence of the universe to a transcendent cause. Scripture is silent on the metaphysics of causation as such, but Scripture's repeated affirmation of God as Creator (*"in the beginning God created the heavens and the earth,"* Genesis 1:1; *"by faith we understand that the worlds were prepared by the word of God, so that what is seen was not made out of things which are visible,"* Hebrews 11:3, NASB95) presupposes the causal framework the cosmological argument formalizes. [Romans 1.20](/codex/romans-1-20/) gives the epistemological warrant for natural theology more broadly: God's invisible attributes are made known through what has been made. Christian philosophers who take CP for granted without engaging the contemporary literature are arguing on ground that an informed opponent can challenge. The defense of CP through Craig, Pruss, Rasmussen, and Koons is therefore not optional ornamentation on natural theology; it is the foundation. ## See also - [Kalam Cosmological Argument](/codex/kalam-cosmological-argument/), the argument the causal principle anchors. - [Cosmological Arguments](/codex/cosmological-arguments/), the family hub. - [Contingency Argument](/codex/contingency-argument/), the Leibnizian sister argument running on PSR. - [Aquinas Five Ways](/codex/aquinas-five-ways/), the Thomistic deployments of causal principles. - [Principle of Sufficient Reason](/codex/principle-of-sufficient-reason/), the stronger Leibnizian relative. - [Meta-Ontology](/codex/meta-ontology/), for the meta-level question of whether existence claims are substantive. - [Meta-Ontological Argument for Theism](/codex/meta-ontological-argument-for-theism/), the debate-prep argument from meta-ontology. - Metaphysics, the parent discipline. - [Naturalism](/codex/naturalism/) and [Materialism](/codex/naturalism/), the worldview positions the cosmological argument challenges. - [Atheism](/codex/atheism/), the position whose strongest replies target the causal principle. - [Christianity](/codex/christianity/), the tradition for which the principle anchors creation doctrine. - [William Lane Craig](/codex/william-lane-craig/), modern Kalam champion. - [Leibniz](/codex/leibniz/), PSR architect. - [Thomas Aquinas](/codex/thomas-aquinas/), scholastic synthesizer of the causal tradition. - [Aristotle](/codex/aristotle/), the four-causes framework underlying the tradition. - [Plato](/codex/plato/), the earliest explicit formulator. - [Augustine](/codex/augustine/), the timeless-causation framework. - [Romans 1.20](/codex/romans-1-20/), natural theology's biblical warrant. - [Hebrews 11.3](/codex/hebrews-11-3/), creation as the framework of causation talk.
## Common questions this page answers **Q: What is the causal principle?** The causal principle is the metaphysical claim that things do not come into existence without a cause. In its most defended modern form (the Kalam formulation by William Lane Craig) it says: *whatever begins to exist has a cause*. The principle has classical roots in Plato, Aristotle, Augustine, and Aquinas, and a stronger relative in Leibniz's Principle of Sufficient Reason. It is the first premise of the cosmological argument for God's existence and the load-bearing dispute in contemporary natural theology. **Q: What is the difference between the causal principle and the Principle of Sufficient Reason?** The causal principle (Kalam form) says: *whatever begins to exist has a cause.* It is restricted to things that come into being. The Principle of Sufficient Reason (Leibniz) is stronger: *everything that exists has a sufficient reason for its existence, either in another or in itself.* PSR applies to all contingent existence, not only to origination, and demands explanation rather than merely a cause. PSR entails the causal principle but goes further. Contemporary defenders (Pruss, Rasmussen, Koons) have developed restricted causal-PSR formulations that try to capture PSR's explanatory power while avoiding its strongest objections. **Q: Does quantum mechanics show that things can come into existence without a cause?** No, despite the popular claim. Quantum-vacuum fluctuations occur in a sea of fluctuating energy governed by determinate physical laws; the vacuum is not the metaphysician's *nothing*. Lawrence Krauss's *A Universe from Nothing* trades on an equivocation between physicists' *nothing* (the quantum vacuum) and metaphysicians' *nothing* (the absence of all being, laws, and physical reality whatever). David Albert's review of Krauss in the *New York Times* (2012) is the canonical critique. Even on interpretations of quantum mechanics where events are not deterministically caused, they are probabilistically caused, and the causal principle is not the deterministic principle. **Q: What was Hume's objection to the causal principle?** David Hume, in the *Enquiry* and the *Treatise*, argued that we have no rational warrant for the necessary connection between cause and effect. We observe constant conjunction (B always follows A) but never observe the necessary tie itself. On his view, the idea of causation is a psychological projection, not a feature of objective reality. Hume went further in the *Dialogues Concerning Natural Religion*: *"it is not absurd to suppose that something might come into existence without a cause."* This is the locus classicus of the modern objection. Theist replies (Pruss 2006 catalogs them) note that Hume's analysis is rejected by most contemporary philosophers of causation, that conceivability is not metaphysical possibility, and that Hume himself relies on causal reasoning throughout his works. **Q: Why does the causal principle matter for the cosmological argument?** It is the first premise. The Kalam Cosmological Argument runs: (1) whatever begins to exist has a cause; (2) the universe began to exist; (3) therefore the universe has a cause. If premise 1 fails, the argument fails. Premise 2 is fought largely on scientific terrain (Big Bang cosmology, the Borde-Guth-Vilenkin theorem). Premise 1 is fought on metaphysical terrain, and the entire defense of the cosmological tradition from Plato through Aquinas through Craig hinges on whether the causal principle can be defended as a necessary metaphysical truth or at least as far more plausible than its negation. **Q: Who are the major contemporary defenders of the causal principle?** William Lane Craig (the Kalam formulation, *The Kalam Cosmological Argument* 1979, *Reasonable Faith* 3rd ed. 2008), Alexander Pruss (PSR and causal PSR, *The Principle of Sufficient Reason: A Reassessment* Cambridge 2006), Joshua Rasmussen (contingent-explanation principles, *Necessary Existence* 2017 with Pruss, *How Reason Can Lead to God* 2019), Robert Koons (formal mereological and modal versions, *Realism Regained* Oxford 2000), and Edward Feser (the Thomistic essentially-ordered series, *Five Proofs of the Existence of God* 2017). The major opponents are J. L. Mackie (*The Miracle of Theism* 1982), Graham Oppy (*Arguing about Gods* 2006), and Lawrence Krauss (the quantum-vacuum line, *A Universe from Nothing* 2012). **Q: Is the causal principle a necessary truth or a contingent generalization?** This is the most consequential question about the principle. If it is a necessary metaphysical truth (true in every possible world), it can do the strong work the cosmological argument asks of it: the universe necessarily has a cause. If it is only a contingent empirical generalization (true in our world but possibly false elsewhere), it can support at most an inductive cosmological argument. Craig, Pruss, Koons, and Feser defend the necessary-truth reading on the grounds that denying the principle amounts to a category error or a failure to grasp what causation is. Hume, Mackie, and Oppy defend the contingent-generalization reading. A third option (Kantian) treats the principle as a transcendental presupposition of intelligible experience: necessary in the sense that we cannot coherently deny it while continuing to think.