Naturalism is the belief that nature is all that exists, and that all things supernatural (including gods, spirits, souls and non-natural values) therefore do not exist. It is often called Metaphysical Naturalism or Philosophical Naturalism or Ontological Naturalism to distinguish it from Methodological Naturalism (see the section on Types of Naturalism below).
It holds that any mental properties that exist (and hence any mental powers or beings) are causally derived from, and ontologically dependent on, systems of non-mental properties, powers or things (i.e. all minds, and all the contents and powers and effects of minds, are entirely constructed from or caused by natural phenomena). Some naturalistic beliefs claim that what is commonly called supernatural is, in fact, part of the natural world.
There are different varieties of Metaphysical Naturalism, but they are usually separated into two general categories:
- Physicalism (or Materialism):
The belief that everything which exists is no more extensive than its physical properties, and that the only existing substance is physical. Thus, everything that has ever been observed is in actual fact the product of fundamentally mindless arrangements or interactions of matter-energy in space-time, and it is unreasonable to believe anything else exists.
The belief that reality consists of many different substances (including abstract objects and universals) in addition to those fundamentally mindless arrangements or interactions of matter-energy in space-time.
Naturalism is inconsistent with any kind of Theism and compatible with Atheism. The direct opposite of Naturalism is Supernaturalism, which accepts the existence of such things as supernatural beings, magical objects, Platonic forms or the existence of love (for example) as a cosmic force.
The earliest Pre-Socratic philosophers, such as Thales, Anaxagoras and especially Democritus, were labelled "natural philosophers" because they sought to explain everything by reference to natural causes alone, often explicitly excluding any role for gods, spirits or magic in the creation or operation of the world.
This eventually led to fully-developed systems such as Epicureanism, which sought to explain everything that exists as the product of atoms moving in a void (Atomism), or the advanced Aristotelianism of Strato of Lampsacus (c. 335 - 269 B.C.), who sought to explain everything that exists as the inevitable outcome of uncreated natural forces or tendencies.
Metaphysical Naturalism is most notably a Western phenomenon, although one tradition within Confucian philosophy (dating back at least to Wang Chong in the 1st Century, if not earlier) embraced a view that could be called Naturalism.
With the rise and dominance of Christianity and the decline of secular philosophy in the West during the Middle Ages, Metaphysical Naturalism became heretical and eventually illegal. It was only when the political advances of the Age of Enlightenment made genuine free speech possible again that a few intellectuals (like Baron d'Holbach in the 18th Century) publicly renewed the case for Metaphysical Naturalism, under the label of Materialism. Later, with scientific advances in quantum physics, this developed into the more far-reaching doctrine of Physicalism.
Certain political philosophies, notably Marxism in the 19th Century and Objectivism in the 20th Century, have embraced Naturalism for their causes, as have the more moderate political ideals of Secular Humanism. Currently, Metaphysical Naturalism is more widely embraced than ever before, especially (but not exclusively) in the scientific community, even if the vast majority of the population of the world remains firmly committed to supernaturalist worldviews.
- Argument from Precedent: For over three hundred years, empirical methods have consistently discovered only natural things and causes, even underlying many things once thought to be supernatural. Hence, we should presume that any unexplained fact has a natural explanation until we have empirically proven otherwise.
- Argument from Best Explanation: Sound naturalist hypotheses about scientifically unexplained facts still out-perform all other hypotheses in explanatory scope and power, and have to resort to fewer ad hoc assumptions than any supernatural alternatives.
- Argument from Absence: If the supernatural does exist (whether as gods, powers or spirits), it is so silent and inert that its effects are almost never observed, despite extensive searching.
- Argument from Physical Minds: Scientists have accumulated vast evidence that the human mind is a product of a functioning brain, which is entirely constructed from different interacting physical systems that evolved over time through the animal kingdom.
- Cosmological Argument: The formation of intelligent life via natural processes is very unlikely unless the universe were immensely old and big, but that is exactly what we have found to be the case, and supernaturalism has not given us any insights into a more likely alternative universe.
- Argument from the Implausibility of Alternatives: In the absence of any reasonable argument to believe anything supernatural exists (or explains anything), and in the presence of some reasonable arguments to believe the natural world exists (and explains everything), then Naturalism should be accepted until disproved (see Ockham's Razor).
The arguments against Naturalism are, to a large extent, arguments for a God, or for some kind of intelligent design (also see the section on Philosophy of Religion):
- Argument from Despair: Naturalism leads to human despair because it allows for no cosmic meaning of life and the elimination of free will (and therefore of hope and moral responsibility).
- Argument from Religious Experience: Many people claim to have seen, felt or talked to God or any number of other spirits, and claim that these religious experiences refute naturalism.
- Argument from Miracles: Often, some miracle is offered as evidence refuting naturalism, including alleged cases of supernatural healing, fulfilled prophetic or psychic predictions, or the supposed impossibility of composing some book (like the Bible or the Koran) without divine aid.
- Argument from Necessity of God: It is in some sense impossible for the universe to exist, and to achieve the apparently impossible feat of life as we know it, unless it is caused or cohabited by a supernatural person.
- Argument from Cosmological Design: The fundamental constants of physics and the laws of nature appear so finely-tuned to permit life that only a supernatural engineer can explain it.
- Argument from Improbability of Life: The origin of life was too improbable (with a probability tending to zero) to have occurred without supernatural intervention and therefore naturalism fails to explain the appearance of life.
- Argument from Biological Design: Certain structures in evolved organisms (e.g. the eye) are too complex ("irreducible complexity") to have evolved by natural selection and can only be explained as the result of intelligent design.
- Argument from Consciousness: Some argue that conscious experience (or qualia) has not been, and cannot be, scientifically explained.
- Argument from Reason: Certain features of human reason (e.g. intentionality, mental causation, abstract objects, the existence of logical laws) cannot be explained by naturalism.
- Argument from Physical Law: The mathematical nature of physical laws entails a supernatural mind behind them, and naturalism can provide no ontological foundation for such physical laws.
- Argument from Incoherence: Because naturalism assumes that everything is physical, using physical data in support of it would constitute circular reasoning.
- Moral Argument: Naturalism cannot explain the existence of moral facts.
- Evolutionary Argument: Maintaining the truth of both naturalism and evolution is irrational and self-defeating because the probability that unguided evolution would have produced reliable cognitive faculties is either low or inscrutable, and so asserting that naturalistic evolution is true also asserts that one has a low or unknown probability of being right.
Naturalism typically leads to the following beliefs:
- The universe has either always existed or had a purely natural origin, being neither created nor designed.
- Life is an unplanned product of blind natural processes and luck.
- Slow and imperfect evolution by natural selection is the explanation for the rise and diversity of life on earth.
- Human beings have no independent soul or spirit, but only a material brain which operates to produce a conscious mind.
- Mental contents (such as ideas, theories, emotions, moral and personal values, beauty, etc) exist solely as the computational constructions of our brains, and not as things that exist independently of us.
- All humans are mortal since the death or destruction of our brain cannot be survived.
- Humans developed (and are now dependent on) culture and civilization, because we evolved as social animals.
- All conduct and behaviour should be directed towards the pursuit of human happiness, that being the greatest value possible for humans.
- Metaphysical Naturalism is the belief (as described in detail above) that nature is all that exists, and that all things supernatural (including gods, spirits, souls and non-natural values) therefore do not exist.
- Methodological Naturalism is the assumption that observable events in nature are explained only by natural causes, without assuming either the existence or non-existence of the supernatural, and so considers supernatural explanations for such events to be outside science. It holds that the scientific method (hypothesize, predict, test, repeat) is the only effective way to investigate reality, and that such empirical methods will only ascertain natural facts, whether supernatural facts exist or not.
Absolute Methodological Naturalism is the view that it is in some sense impossible for any empirical method to discover supernatural facts, even if there are some.
- Contingent Methodological Naturalism is the view that, from past experience, empirical methods are far more likely to uncover natural facts than supernatural ones, so that it is generally an ill-advised waste of resources to pursue supernatural hypotheses, but it would not be impossible to confirm them empirically if any were found.
- Humanistic Naturalism holds that human beings are best able to control and understand the world through use of the scientific method, because concepts of spirituality, intuition and metaphysics can never progress beyond personal opinion. Everything is regarded as a result of explainable processes within nature, with nothing lying outside of it.
- Ethical Naturalism (or Moral Naturalism) is the meta-ethical theory that ethical terms can be defined without the use of ethical terms (such as "good", "right", etc), and moreover that these non-ethical terms refer to natural properties (as opposed to relating the ethical terms in some way to the will of God).
- Sociological Naturalism is the sociological theory that the natural world and the social world are roughly identical and governed by similar principles. It is closely connected to Positivism, which advocates use of the scientific method of the natural sciences in studying social sciences.
- In addition, Naturalism is also an artistic style (referring to the depiction of realistic objects in a natural setting), and a literary, cinematic and theatrical style (referring to the attempt to replicate a believable everyday reality, as opposed to a symbolic, idealistic or even supernatural treatment).