The first Greek naturalists were nicknamed simply the nature people
Long before modern science, thinkers like Thales and Democritus explained the world without gods, and their peers dubbed them the physikoi, from the Greek word for nature. Naturalism, the view that only natural laws and forces operate in the universe, has roots in Greece, ancient India and China alike.
In its strong form, often called metaphysical or ontological naturalism, the position says every cause lies inside the universe, with nothing transcendent behind it. The humanist philosopher Paul Kurtz put it in terms of matter, energy and other properties accepted by science, and concluded that spirits, gods and ghosts are unreal and that nature has no built-in purpose. A milder version, methodological naturalism, simply adopts natural explanations as a working rule without ruling on whether they are the whole truth. Naturalism overlaps with materialism and physicalism, but philosophers draw distinctions among them.
The Milesian thinkers and the atomists Leucippus and Democritus looked for natural causes and often left gods out of the story. Archelaus carried the approach to Athens, and it culminated in Epicureanism, which explained everything as atoms falling and swerving through empty space. Plato countered with eternal Forms shaped into matter by a divine craftsman, and the Stoics also saw purpose in nature. Aristotle, after early sympathy with design, charted a middle path: his Prime Mover does not build or arrange the cosmos, yet he rejected blind mechanism in favour of an idea of nature itself.
Parallel ideas arose in the East. Samkhya, one of the oldest schools of Indian philosophy, treats nature, Prakriti, as the primary cause without assuming a personal God, and naturalism underpins the Nyaya and Vaisheshika schools as well as the heterodox Carvaka. In China a naturalist current within Confucian thought goes back at least to Wang Chong in the 1st century, though it had little later influence.
Once Christianity and then Islam dominated, intellectuals largely abandoned metaphysical naturalism, and medieval philosophy shows little trace of it. Most theists deny that nature is all there is, sometimes treating natural laws as God's secondary causes, though pantheists identify nature with the divine. In the 20th century Willard Van Orman Quine and George Santayana argued that science's success means philosophy should use its methods, the two forming a continuum.
Source: Naturalism (philosophy)
