Natural Theology

Introduction

Natural theology is the project of establishing or defending substantive conclusions about God's existence, nature, and providence using reason alone, without appeal to revelation, scripture, or ecclesial authority. Its arguments take publicly available premises — the existence of the cosmos, the structure of causation, the apparent design of organisms, the universal phenomenon of moral conscience, the conceivability of a maximally perfect being — and attempt to derive theistic conclusions that any rational inquirer should accept. The discipline organizes the most familiar arguments in the philosophy of religion: the ontological argument, the cosmological argument, the argument from design, the moral argument, and arguments from religious experience. It also organizes the most familiar attacks on theism, since each argument has generated its own critical literature.

The discipline has been the central engine of philosophical theology in the Latin West from Augustine through Aquinas through Leibniz through twentieth-century analytic philosophy of religion. It has also been the most contested project in Christian theology, both from within (Reformed objections to its possibility) and from without (Hume, Kant, and twentieth-century non-cognitivism).

The problem it answers

Natural theology answers the question of whether religious claims can be adjudicated by the same kinds of reasoning that adjudicate scientific, metaphysical, and ethical claims. If yes, theism is in principle defensible to any rational person, theist or not — religious knowledge belongs to philosophy, not only to faith. If no, theism is a stance taken on grounds other than reason, and the only honest response is fideism, skepticism, or some non-cognitivist account of religious language.

The discipline thus stakes out the terrain shared between philosophy and theology. It treats the question of God's existence as a metaphysical question susceptible to evidence and inference, parallel to questions about substance, causation, modality, or mind.

Core claim

The core claim of natural theology has three parts. First, propositions about God — that God exists, that God is necessary, that God is the cause of the world's contingent existence, that God is intelligent — are propositions that can be the conclusions of valid arguments from premises available to unaided reason. Second, the relevant premises are publicly available: features of the world (existence, motion, order), features of concepts (perfection, necessity), or features of human nature (moral consciousness, the desire for the infinite) that any rational inquirer can investigate. Third, the conclusions of these arguments warrant rational assent independently of revelation; they are not merely confirmations of what scripture already teaches but free-standing pieces of metaphysical knowledge.

Natural theology does not claim that revelation is dispensable. The standard scholastic position, formalized by Thomas Aquinas, is that natural reason can establish a limited set of theological truths (God's existence, oneness, eternity, providence) but cannot reach the doctrines that depend on revelation (the Trinity, the Incarnation, the resurrection of the body). Reason and revelation are distinct but harmonious sources of theological knowledge.

History in one paragraph

The project has antecedents in Plato's argument from motion in Laws X and Aristotle's argument for an unmoved mover in Metaphysics Λ. The Stoics developed cosmological-providential arguments preserved in Cicero's De Natura Deorum (45 BCE). Augustine (354–430) gave Christian natural theology its first systematic shape, particularly in De Trinitate. Anselm of Canterbury (1033–1109) inaugurated the ontological argument in the Proslogion (1077–78). Aquinas (1225–1274) gave the cosmological arguments their canonical formulation in the Five Ways of Summa Theologiae Ia q.2 a.3 (c. 1265–74). Duns Scotus and William of Ockham refined the arguments and their metaphysical commitments. The early-modern period saw Descartes revive the ontological argument in the Meditations (1641) and Leibniz reformulate the cosmological argument via the principle of sufficient reason. William Paley's Natural Theology (1802) gave the argument from design its most famous English-language statement. David Hume in the Dialogues Concerning Natural Religion (1779) and Immanuel Kant in the Critique of Pure Reason (1781) mounted the canonical Enlightenment critiques. Karl Barth's Nein! (1934) gave the dialectical-theological rejection. Analytic philosophy of religion since Alvin Plantinga's God and Other Minds (1967) and The Nature of Necessity (1974) has revived natural theology with new logical resources.

The classical arguments

Natural theology is most easily approached through its five canonical argument families.

The cosmological argument reasons from the existence of the contingent world to a necessary first cause. The argument takes three principal forms: the kalam version (associated with the Islamic mutakallimūn and revived by William Lane Craig), which argues that the universe began to exist and therefore has a cause; the Thomistic version (Aquinas's Second Way), which argues from the impossibility of an infinite per se causal regress to an uncaused cause sustaining the present; and the Leibnizian version, which argues from the principle of sufficient reason to a necessary being whose existence explains the contingent series.

The ontological argument reasons from the concept of God as that than which nothing greater can be conceived to the conclusion that God exists. Anselm's original formulation in Proslogion 2–3 has been reformulated by Descartes (the perfect-being argument), Leibniz (the possibility-to-actuality move), Norman Malcolm and Charles Hartshorne (the necessary-existence version), and Plantinga (the modal version in The Nature of Necessity).

The argument from design reasons from the apparent purposiveness of features of the world — the eye, the orderly motion of the planets, the fine-tuning of physical constants — to an intelligent designer. The classical form is Paley's watchmaker analogy in Natural Theology (1802). Darwin's Origin of Species (1859) is widely taken to have refuted the biological version, though contemporary fine-tuning arguments (Robin Collins, Luke Barnes) have revived a cosmological version.

The moral argument reasons from the existence of objective moral obligations or values to a divine ground for them. Kant's version in the Critique of Practical Reason (1788) treats God as a postulate of practical reason; contemporary versions associated with C. S. Lewis, Robert Adams, and John Hare argue that moral facts require theistic explanation.

The argument from religious experience reasons from widespread reports of perceived encounter with the divine to the conclusion that such experience constitutes evidence for theism. William Alston's Perceiving God (1991) developed the most sophisticated contemporary version, arguing that religious perception has the same epistemic structure as sense perception.

Method and method-disputes

Natural theology divides internally on how its arguments are supposed to function. Three positions are well-developed.

The strong demonstrative tradition, associated with high scholasticism and rationalist metaphysics, holds that natural-theological arguments are demonstrations in the strict sense — they yield certain conclusions from self-evident or rationally compelled premises. Aquinas's Five Ways and Leibniz's cosmological argument are presented in this register.

The probabilistic tradition, associated with eighteenth-century natural religion and contemporary analytic philosophy of religion, holds that natural-theological arguments are evidence-confirming rather than demonstrative. Richard Swinburne's The Existence of God (1979, second edition 2004) is the model: each argument raises the probability of theism, and their cumulative effect is to make theism more probable than not.

The reformed-epistemological tradition, associated with Plantinga and Nicholas Wolterstorff, holds that belief in God can be properly basic — rationally held without being the conclusion of any argument — and that natural theology, while not necessary for rational theistic belief, can play a confirming or defensive role. Plantinga's Warranted Christian Belief (2000) develops this position systematically.

The major critiques

Three lines of criticism define the contours of the discipline.

Hume's Dialogues (1779, published posthumously) is the canonical critique. The argument runs against design (the world's apparent order admits naturalistic explanation and, in any case, is inconsistent with the world's apparent disorder), causation (the causal principle cannot be extended from intramundane causation to the cosmos as a whole), and analogy (the world is too unlike the products of human design for the analogy to support its conclusion). Hume's critique remains the starting point for contemporary atheistic philosophy of religion.

Kant's critique in the Transcendental Dialectic of the Critique of Pure Reason (1781) is more radical. Kant argues that the ontological, cosmological, and physico-theological arguments all rest on the ontological argument, which fails because existence is not a real predicate. The cosmological argument illicitly extends categories of the understanding beyond possible experience; the design argument at best establishes an architect of the world's matter, not its creator. Natural theology as a theoretical discipline is impossible; God can be admitted only as a postulate of practical reason.

Karl Barth's Nein! (1934), written against Emil Brunner, gives the twentieth-century dialectical-theological rejection. Barth holds that natural theology is theologically illegitimate because it implies that the human knower can ascend to God by their own powers, contradicting the doctrine of the radical priority of grace and the analogia entis — the rejection of any analogy of being between creature and creator that would license natural-theological inference. The Barthian critique has shaped twentieth-century Reformed theology and continues in the work of John Webster and Bruce McCormack.

Common confusions

Natural theology is not the same as natural religion. Natural religion is the religious practice and belief held to be available to unaided human reason — the deists' minimal theism, the Enlightenment's universal religion of nature. Natural theology is the philosophical discipline that examines whether such belief is rationally warranted. One can practice natural theology without endorsing natural religion (Aquinas), and one can endorse natural religion without practicing rigorous natural theology (the popular deists).

Natural theology is not the same as philosophy of religion. Philosophy of religion is the broader field, including the philosophy of religious language, the epistemology of religious belief, comparative philosophy of religion, and the philosophical analysis of specific religious doctrines (atonement, resurrection, providence). Natural theology is one project within philosophy of religion, focused on the question of theistic belief's rational warrant.

Natural theology is not apologetics. Apologetics is the defense of a specific religious tradition's truth against criticism, conducted for the sake of believers or potential converts. Natural theology may be used in apologetic projects, but the discipline itself is not bound to confessional commitments — Aristotle, Cicero, and contemporary secular philosophers can operate in the same logical space as Christian theologians.

Live debates

Several internal debates structure the contemporary discipline.

The probabilistic-versus-demonstrative dispute remains active. Swinburne argues for cumulative-case probabilistic natural theology; Edward Feser in Five Proofs of the Existence of God (2017) defends the older demonstrative tradition, arguing that contemporary probabilism concedes too much to Humean assumptions.

The fine-tuning literature has generated its own active debate. Collins and Barnes argue that the apparent fine-tuning of physical constants for life requires explanation and that theism is a better explanation than the multiverse alternative; opponents (Sean Carroll, Victor Stenger) argue that the apparent fine-tuning is illusory or that the multiverse explanation is superior. The debate has been shaped by recent work in cosmology and the philosophy of probability.

The reformed-epistemology dispute concerns whether natural theology is necessary at all. Plantinga's position that theistic belief can be properly basic has been challenged by William Lane Craig (who insists on the importance of arguments) and by atheistic philosophers who argue that proper basicality is too permissive — if theistic belief is properly basic, so is voodoo belief.

The methodological dispute about explanatory style is live: should natural theology aim at inference to the best explanation (Swinburne, Collins), at strict demonstration (Feser), at cumulative probability (Swinburne), or at the defense of properly basic belief (Plantinga, Wolterstorff)?

Contemporary engagement

Contemporary analytic philosophy of religion has been a sustained revival of natural theology since the 1960s. The central figures include Alvin Plantinga (whose Warranted Christian Belief, 2000, completes the trilogy begun with Warrant: The Current Debate, 1993, and Warrant and Proper Function, 1993), Richard Swinburne (whose tetralogy The Coherence of Theism, 1977; The Existence of God, 1979; Faith and Reason, 1981; and Responsibility and Atonement, 1989, established the probabilistic program), William Lane Craig (whose The Kalam Cosmological Argument, 1979, and ongoing work with J. P. Moreland have rebuilt the kalam tradition), Edward Feser (whose Thomistic revival in The Last Superstition, 2008, and Five Proofs of the Existence of God, 2017, has revived strict demonstrative natural theology), and Robin Collins (whose decades of work on the fine-tuning argument set the contemporary terms of that debate). The journals Faith and Philosophy, Religious Studies, the International Journal for Philosophy of Religion, and Philosophia Christi publish the active scholarship. The Society of Christian Philosophers organizes the field institutionally.

Atheist critics have organized in parallel. Graham Oppy's Arguing about Gods (2006) and The Best Argument against God (2013) are the most systematic contemporary atheistic engagements with natural theology. J. L. Mackie's The Miracle of Theism (1982) remains a standard reference. J. L. Schellenberg's argument from divine hiddenness (developed across Divine Hiddenness and Human Reason, 1993, and subsequent works) is the most influential atheistic argument to emerge since Mackie. Paul Draper's work on the problem of evil sets the contemporary terms of that debate.

The discipline also remains active in Catholic and Reformed theology proper. The encyclical Fides et Ratio (1998) gave a magisterial defense of natural theology's compatibility with Christian faith. Reformed thinkers including Michael Sudduth (The Reformed Objection to Natural Theology, 2009) have re-examined the historic Reformed engagement with the discipline, complicating the standard story of Barthian rejection.

Further reading

• Ontological Argument — the a priori argument from concept to existence; central to natural theology's modal wing.
• Cosmological Argument — the a posteriori argument from contingency to necessity; the most discussed family.
• Problem of Evil — the principal countervailing argument; defines the natural-theological agenda from the other direction.
• Theodicy — the constructive theistic response to the problem of evil; operates within the natural-theological frame.
• Thomas Aquinas — the canonical scholastic systematization of the discipline.
• David Hume — the canonical critic.
• Summa Theologiae — Ia qq.2–13 contain the classical natural-theological program.

Natural theology is the discipline that asks whether reason alone can deliver substantive conclusions about God — and remains the central battlefield of philosophy of religion.