As defined by philosopher Paul Draper, naturalism is "the hypothesis that the natural world is a closed system" in the sense that "nothing that is not a part of the natural world affects it." More simply, it is the denial of the existence of supernatural causes. In rejecting the reality of supernatural events, forces, or entities, naturalism is the antithesis of supernaturalism.

As a substantial view about the nature of reality, it is often called metaphysical naturalism, philosophical naturalism, or ontological naturalism to distinguish it from a related methodological principle. Methodological naturalism, by contrast, is the principle that science and history should presume that all causes are natural causes solely for the purpose of promoting successful investigation. The idea behind this principle is that natural causes can be investigated directly through scientific method, whereas supernatural causes cannot, and hence presuming that an event has a supernatural cause for methodological purposes halts further investigation. For instance, if a disease is caused by microbes, we can learn more about how microbes interact with the body and how the immune system can be activated to destroy them, or how the transmission of microbes can be contained. But if a disease is caused by demons, we can learn nothing more about how to stop it, as demons are said to be supernatural beings unconstrained by the laws of nature (unlike natural causes).

In utilizing methodological naturalism, science and history do not assume a priori that, as a matter of fact, supernatural causes don't really exist. There is no conceptual conflict between practicing science or history and believing in the supernatural. However, as several of our authors argue below (e.g., Augustine, Fales, Forrest, and Oppy), methodological naturalism would not be as stunningly successful as it has in fact been if metaphysical naturalism were false. Thus the de facto success of methodological naturalism provides strong empirical evidence that metaphysical naturalism is probably true.

-- Keith Augustine

Naturalism is not so much a special system as a point of view or tendency common to a number of philosophical and religious systems; not so much a well-defined set of positive and negative doctrines as an attitude or spirit pervading and influencing many doctrines. As the name implies, this tendency consists essentially in looking upon nature as the one original and fundamental source of all that exists, and in attempting to explain everything in terms of nature. Either the limits of nature are also the limits of existing reality, or at least the first cause, if its existence is found necessary, has nothing to do with the working of natural agencies. All events, therefore, find their adequate explanation within nature itself. But, as the terms nature and natural are themselves used in more than one sense, the term naturalism is also far from having one fixed meaning.

  • (I) If nature is understood in the restricted sense of physical, or material, nature, naturalism will be the tendency to look upon the material universe as the only reality, to reduce all laws to mechanical uniformities and to deny the dualism of spirit and matter. Mental and moral processes will be but special manifestations of matter rigorously governed by its laws.
  • (II) The dualism of mind and matter may be admitted, but only as a dualism of modes or appearances of the same identical substance. Nature includes manifold phenomena and a common substratum of the phenomena, but for its actual course and for its ultimate explanation, it requires no principle distinct from itself. In this supposition, naturalism denies the existence of a transcendent cause of the world and endeavours to give a full account of all processes by the unfolding of potencies essential to the universe under laws that are necessary and eternal.
  • (III) Finally, if the existence of a transcendent First Cause, or personal God, is admitted as the only satisfactory explanation of the world, Naturalism claims that the laws governing the activity and development of irrational and of rational beings are never interfered with. It denies the possibility, or at least the fact, of any transitory intervention of God in nature, and of any revelation and permanent supernatural order for man.

These three forms are not mutually exclusive; what the third denies the first and the second, a fortiori, also deny; all agree in rejecting every explanation which would have recourse to causes outside of nature. The reasons of this denial — i.e., the philosophical views of nature on which it is based — and, in consequence, the extent to which explanations within nature itself are held to suffice, vary greatly and constitute essential differences between these three tendencies.

Materialistic naturalism

Materialistic Naturalism asserts that matter is the only reality, and that all the laws of the universe are reducible to mechanical laws. What theory may be held concerning the essence of matter makes little difference here. Whether matter be considered as continuous or as composed of atoms distant from one another, as being exclusively extension or as also endowed with an internal principle of activity, or even as being only an aggregate of centres of energy without any real extension (see ATOMISM; DYNAMISM; MECHANISM), the attitude of Naturalism is the same. It claims that all realities in the world, including the processes of consciousness from the lowest to the highest, are but manifestations of what we call matter, and obey the same necessary laws. While some may limit their materialistic account to nature itself, and admit the existence of a Creator of the world, or at least leave this question open, the general tendency of Materialism is towards Atheism and exclusive Naturalism. Early Greek philosophers endeavoured to reduce nature to unity by pointing to a primordial element out of which all things were composed. Their views were, implicitly at least, Animistic or Hylozoistic rather than Materialistic, and the vague formative function attributed to the Nous, or rational principle, by Anaxagoras was but an exception to the prevailing naturalism. Pure mechanism was developed by the Atomists (Democritus, Epicurus, Lucretius), and the soul itself was held to be composed of special, more subtile, atoms. In the Christian era materialism in its exclusive form is represented especially by the French school of the latter half of the eighteenth century and the German school of the latter half of the nineteenth century. Since matter is the only reality, whatever takes place in the world is the result of material causes and must be explained by physical antecedents without any teleology. Life is but a complex problem of physics and chemistry; consciousness is a property of matter; rational thought is reduced to sensation, and will to instinct. The mind is a powerless accompaniment or epiphenomenon of certain forms or groupings of matter, and, were it suppressed altogether, the whole world would still proceed in exactly the same way. Man is a conscious automaton whose whole activity, mental as well as physiological, is determined by material antecedents. What we call the human person is but a transitory phase in the special arrangement of material elements giving rise to special mental results; and it goes without saying that in such a system there is no room for freedom, responsibility, or personal immortality.


Pantheism in its various forms asserts that God, the First Reality, World-Ground, or Absolute, is not transcendent and personal, but immanent in the world, and that the phenomena of nature are only manifestations of this one common substance. For the Stoics, He is the immanent reason, the soul of the world, communicating everywhere activity and life. According to Scotus Eriugena, "God is the essence of all things, for He alone truly is" (De divisione naturæ, III); nature includes the totality of beings and is divided into

  1. uncreated and creating nature, i.e., God as the origin of all things, unknowable even to Himself;
  2. created and creating nature, i.e., God as containing the types and exemplars of all things;
  3. created and not-creating nature, i.e., the world of phenomena in space and time, all of which are participations of the Divine being and also theophaniœ, or manifestations of God;
  4. neither created nor creating nature, i.e., God as the end of all things to whom all things ultimately return.

Giordano Bruno also professes that God and nature are identical, and that the world of phenomena is but the manifestation of the Divine substance which works in nature and animates it. According to Spinoza, God is the one substance which unfolds itself through attributes, two of which, extension and thought, are known to us. These attributes manifest themselves through a number of modes which are the finite determinations of the infinite substance. As absolute substance, God is natura naturans; as manifesting himself through the various modes of phenomena, he is natura naturata. Today Monism reproduces essentially the same theories. Mind is not reduced to a property, or epiphenomenon, of matter, but both matter and mind are like parallels; they proceed together as phenomena or aspects of the same ultimate reality. What is this reality? By some, explicitly or implicitly, it is rather conceived as material, and we fall back into Materialism; by others it is claimed to be nearer to mind than to matter, and hence result various idealistic systems and tendencies; by others, finally, it is declared to be strictly unknown and unknowable, and thus Monistic Naturalism comes into close contact with Agnosticism.

Whatever it may be ultimately, nature is substantially one; it requires nothing outside of itself, but finds within itself its adequate explanation. Either the human mind is incapable of any knowledge bearing on the question of origins, or this question itself is meaningless, since both nature and its processes of development are eternal. The simultaneous or successive changes which occur in the world result necessarily from the essential laws of nature, for nature is infinitely rich in potencies whose progressive actualization constitutes the endless process of inorganic, organic, and mental evolution. The evolution and differentiation of the one substance according to its own laws and without the guiding agency of a transcendent intelligence is one of the basic assumptions of Monistic and Agnostic Naturalism. Nor is it possible to see how this form of Naturalism can consistently escape the consequences of Materialistic Naturalism. The supernatural is impossible; at no stage can there be any freedom or responsibility; man is but a special manifestation or mode of the common substance, including in himself the twofold aspect of matter and consciousness. Moreover, since God, or rather "the divine", as some say, is to be found in nature, with which it is identified, religion can only be reduced to certain feelings of admiration, awe, reverence, fear, etc., caused in man by the consideration of nature its laws beauties, energies, and mysteries. Thus, among the feelings belonging to "natural religion", Haeckel mentions "the astonishment with which we gaze upon the starry heavens and the microscopic life in a drop of water, the awe with which we trace the marvellous working of energy in the motion of matter, the reverence with which we grasp the universal dominance of the law of substance throughout the universe" ("Die Welträthsel", Bonn, 1899, V, xviii, 396-97; tr. McCabe, New York, 1900, 344).

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