Naturalism

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Naturalism is the philosophical position that nature is all there is: that whatever exists belongs to a single natural order, governed by the same kinds of cause and law throughout, with nothing standing outside or above it. There is no separate supernatural realm, no order of being unreachable by inquiry. The word covers a family of related commitments rather than one fixed doctrine, but at the center of all of them is that refusal to grant anything a place beyond nature.

A Renaissance manuscript of Lucretius’s Epicurean poem De rerum natura, copied in 1483 — one of the oldest sustained attempts to explain the world by causes within it. — via Wikimedia Commons (public domain)

It is useful to separate two strands that often travel together. Metaphysical naturalism is a claim about what exists — that the world is exhausted by natural things and their properties, leaving no room for gods, disembodied souls, or immaterial powers. Methodological naturalism is narrower and more cautious: it holds only that inquiry should proceed as though natural explanations were the ones to seek, without pronouncing on whether anything lies beyond their reach. The two are distinct, and a thinker can hold the method while remaining agnostic about the metaphysics; much of modern science operates on the method alone. The distance between them is the whole drama of the position. A scientist who, in the laboratory, looks only for natural causes need make no claim that natural causes are the only causes there are; the method commits one to a search, the metaphysics to a verdict. Naturalism’s critics and its defenders have spent much of the last century arguing over whether the one slides inevitably into the other — whether to work as though nature were closed is, in the end, to believe it.

Two claims, kept apart

Drawn out fully, the two strands answer different questions and rest on different grounds. Metaphysical, or ontological, naturalism is a thesis about the furniture of reality: it says that the inventory of what exists contains natural items only, and that the apparently non-natural — minds, values, numbers, moral facts — must either be located within nature or explained away. In denying that any god belongs to that inventory it draws close to atheism, though the two are not the same: one can be a metaphysical naturalist who holds the question of the divine simply undecidable, closer to agnosticism than to outright denial, and naturalism’s quarrel is less with belief in God than with the supposition of any power standing outside the natural order. Its sharpest modern form is physicalism, the claim that everything that exists is physical, or is fixed by and depends upon the physical, with nothing floating free of the matter-energy that physics describes. Naturalism is broader than physicalism: one can hold that the world is a single natural order while resisting the reduction of everything to physics, leaving room for emergent biological or mental properties that are natural without being merely physical. But in the dominant current of recent metaphysics the two travel close together, and for many writers naturalism just is physicalism worn loosely.

Methodological naturalism makes no such claim about contents. It is a thesis about procedure — about how knowledge is to be pursued and what counts as an explanation. On this view, the only legitimate way to understand any phenomenon, including mind, society, and religion itself, is to study it as one studies anything else in nature: by observation, hypothesis, and the disciplined use of reason to trace causes that lie within the world. It says nothing, officially, about whether gods or souls exist; it says only that they cannot be invoked as explanations within inquiry. The two naturalisms can therefore come apart in either direction. A believer can practice methodological naturalism in the laboratory and reject metaphysical naturalism in the chapel; a thoroughgoing metaphysical naturalist may grant that some questions are not best approached by the methods of science. Much of modern science runs on the method while staying officially silent on the metaphysics — which is precisely why the relation between the two has become one of the most contested borders in modern philosophy.

The old impulse: matter, the swerve, and the immanent reason

The impulse is old. Long before there was a word for it, Greek thought already contained the move that defines naturalism — the move of looking for the world’s workings inside the world rather than above it. The atomism of Democritus, and after him the Epicureans, tried to account for everything through matter in motion: indivisible bodies falling through an infinite void, colliding, combining, and dissolving, with no purpose steering them and no maker behind them. Lucretius set that program to verse in De Rerum Natura, our fullest surviving Epicurean source and the sole witness to the doctrine of the clinamen, the minute, uncaused swerve by which falling atoms first meet and a world begins. He wrote, by his own declaration, to free people from the fear of the gods and the fear of death — to show that the soul is itself made of atoms and perishes with the body, and that the gods, if they exist at all, dwell apart in the spaces between worlds, untroubled by human affairs and uninterested in human worship. Here the explanatory ambition of later naturalism is already fully formed: nothing is to be referred to a power outside the order of things.

Zeno of Citium, founder of the Stoic school, in a 17th-century engraving from Thomas Stanley’s History of Philosophy. — via Wikimedia Commons (public domain)

The Stoics took a different route to a kindred end. They spoke of physis — nature — as an immanent ordering reason pervading the cosmos rather than ruling it from outside. For them the world was one living, rational, providential whole, and the logos, the rational principle by which all things are disposed, was not a transcendent legislator handing down decrees but the very structure of the world thinking itself from within. To grasp nature was to grasp god, because nature and god were one. This is the standing posture of immanence: the divine located in the world rather than beyond it, the position that pantheism would later make explicit. None of these ancient programs was naturalism in the modern sense. They were dense with the divine — the Epicurean cosmos still had its serene gods, the Stoic cosmos was itself a god, the world-soul and the logos ran through everything. What they shared with the later position was the single decisive move: the refusal to step outside the order of things to explain the order of things. They naturalized the explanation while keeping the gods inside nature, not above it — and that is a different settlement from the one the modern term records.

The modern crystallization

The term itself, and the sharpened opposition between the natural and the supernatural, belongs to the modern period. An early modern foretaste came inside Aristotelianism itself, where the Renaissance Alexandrists read the soul as so bound to the body that it died with it — a naturalizing of one corner of the inherited picture, though carried out within a frame that still left the cosmos full of higher orders. The seventeenth-century mechanical philosophy went much further: it redescribed the cosmos as matter governed by law, draining the world of the souls, sympathies, and occult powers that had populated the Renaissance picture — and in doing so it drew, for the first time as a hard line, the boundary between what nature could do on its own and what required an intervention from outside it. The Enlightenment pressed the natural order further, extending the reach of law from the heavens to society and the mind; the empiricist insistence that all knowledge arises from experience and the later program of positivism, which would admit only what the sciences could establish, both narrowed the field of the admissible toward the natural alone. But the word came into its own, and naturalism became the default frame of much academic philosophy, only in the nineteenth and twentieth centuries, when the cumulative success of the sciences made the natural order look not merely the most fruitful field of inquiry but, increasingly, the whole of it. Darwin’s account of the origin of species in 1859, by bringing life and mind under the same kinds of explanation that governed matter, removed what had seemed the last secure refuge of design, and the methodological habit hardened, for many, into a metaphysical conviction.

Charles Darwin, photographed by Julia Margaret Cameron around 1868. His 1859 account of the origin of species brought life and mind under natural explanation. — Julia Margaret Cameron, via Wikimedia Commons (public domain)

The position acquired its name and its manifestos in the twentieth century, above all in America. The mid-century volume Naturalism and the Human Spirit, edited by Yervant H. Krikorian and published by Columbia University Press in 1944, gave the movement a charter: in essays by John Dewey, Sidney Hook, Ernest Nagel, and others, naturalism was advanced not as a denial of value, beauty, or freedom but as the claim that these too belong within nature and are to be understood there — Dewey’s contribution arguing against what he called antinaturalism in its extreme forms.

John Dewey in 1902, a leading contributor to the mid-century American naturalist movement that sought to keep value, mind, and freedom inside nature. — via Wikimedia Commons (public domain)

A generation later W. V. O. Quine, in his 1969 essay Epistemology Naturalized, drew the boldest consequence: that philosophy itself has no station above the sciences from which to certify them. There is no first philosophy, Quine held — no foundation prior to or higher than natural knowledge; epistemology becomes continuous with, even a chapter of, natural science, the study of how knowing creatures actually come to know. With Quine the method turned reflexively on its own discipline, and naturalism passed from a thesis philosophers held about the world into a thesis about how philosophy should be done.

The phrase methodological naturalism is itself recent. Though the practice is old, the explicit label was introduced by the philosopher Paul de Vries, who used it at a conference in 1983 and published it in 1986, precisely in order to mark off a disciplinary method that says nothing about God’s existence from a metaphysical naturalism that denies it; the term was carried into wide use, especially in debates over science and religion, in the work of Robert T. Pennock from the 1990s onward. That a distinction so basic to the position should have waited until the late twentieth century for a settled name is a measure of how recently naturalism became self-conscious about the difference between the way it works and the world it claims.

The argument from the closure of the physical

Behind much contemporary metaphysical naturalism lies a single line of argument, given its most influential modern statement by David Papineau: the argument from the completeness, or causal closure, of the physical. The claim is that all physical effects have sufficient physical causes — that if one traces backward the chain of events producing any physical occurrence, one never has to leave the physical order to find a cause adequate to it. The theoretical and empirical case for this closure, on Papineau’s reading, built up slowly across the modern sciences and became compelling only around the middle of the twentieth century, as physiology and physics closed the apparent gaps where an immaterial mind or vital force might once have reached in. If the physical is causally closed, then anything that makes a difference in the physical world — including the mind, if mental states are to do any work — must itself be physical, on pain of being a cause that produces effects already fully accounted for. This is the spine of the case for physicalism, and through it for the broader naturalism that physicalism serves. The argument is contested at every joint: critics question whether closure is established rather than assumed, whether it quietly presupposes the very conclusion it is meant to support, and whether emergent or naturalistic-dualist pictures — or a panpsychism that builds mind into the physical from the ground up — can honor closure while still leaving genuine work for the mental. The debate is unsettled and technical, but its shape shows what modern naturalism rests on — not a dogma that the supernatural cannot exist, but an inference from the apparent self-sufficiency of the natural order, read off the cumulative success of the sciences in finding causes without ever leaving the world.

What naturalism stands against

Naturalism is best understood by what it sets itself against. It is the position that the larger part of religious, mystical, and esoteric thought rejects, and against which those traditions partly define themselves — for each of them asserts precisely what naturalism denies: an order of reality the senses and the sciences do not reach, and a knowing that arrives from beyond the natural. The Neoplatonist holds that the sensible world hangs from an intelligible order above it, the One overflowing into Intellect and Soul, so that nature is the lowest term of a descent and not the whole of being. The contemplative of the mystical traditions claims a union or a vision that no natural faculty could supply, a knowing that breaks in from elsewhere. The currents of esotericism hold that the world is laced with hidden correspondences and powers that the disenchanted natural order cannot register. Each of these is, structurally, the denial of naturalism’s founding refusal — each insists on exactly the order beyond nature that naturalism declines to grant. The relation runs the other way as well: naturalism takes much of its sharpness from having these as its standing opponents, and the modern boundary between the natural and the supernatural was drawn as much by what it excluded as by what it claimed. To read those traditions on their own terms is to take seriously a claim naturalism rules out at the start; to read naturalism on its own terms is to treat that exclusion not as prejudice but as a disciplined commitment to seeking causes within the world. That tension is a genuine one, and it is not resolved by noticing it.

Whether nature is the whole of what there is remains exactly the question the traditions and their critics have always divided over; naturalism is one of the two answers, stated plainly and held without appeal to anything further.

Scholarship and the textual record

The reference statement of contemporary naturalism is David Papineau’s article Naturalism in the Stanford Encyclopedia of Philosophy, first published in 2007 and substantively revised since, which both organizes the ontological-versus-methodological distinction and presses the causal-closure argument for physicalism that has shaped the recent debate. The Internet Encyclopedia of Philosophy’s survey of naturalism traces the position’s ancient antecedents alongside its modern crystallization. The movement’s own foundational document is the 1944 collection Naturalism and the Human Spirit, edited by Yervant H. Krikorian, whose essays by Dewey, Hook, Nagel, and their colleagues remain the clearest statement of the mid-century American naturalists’ aim — to keep value, mind, and freedom inside nature rather than abolish them. The turn that made philosophy itself a natural science is set out in Quine’s Epistemology Naturalized (1969); the rise of the completeness-of-physics premise that underwrites the modern metaphysical argument is reconstructed in Papineau’s Thinking about Consciousness (2002) and in the essays gathered in The Blackwell Companion to Naturalism (2016). For the ancient sources, the standard philosophical accounts of the atomist and Stoic programs — including the Stanford Encyclopedia’s treatment of Lucretius — recover the explanatory move of looking for causes inside the world in its first, god-filled form, the form in which it was practiced for centuries before the modern term arrived to name a version of it that had emptied the world of the gods the ancients kept within it.

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