Naturalism is about as old as the few religions which still survive to challenge it. The so-called “Axial Age” from around 800 BCE to 300 BCE saw a sudden explosion of religious and philosophical creativity in Europe, the Middle East, India, and China. Greek philosophy and science was invented; Judaism became monotheistic; Zoroasterianism enveloped the Persian empire; Hinduism was transformed by the Vedanta theology in the Upanishads; Buddhism arose to challenge Hinduism; Taoism was systematized in the Tao Te Ching; and Confucianism was founded.
What caused this sudden eruption of sophisticated thought? There are two main explanations, and these hypotheses are compatible with each other. First, all four of the main centers of civilization — Europe, the Middle East, India, and China – were suffering from political fragmentation and civil wars. Much of the moral and political philosophy from the Axial Age arose in efforts to deal with these severe political crises. Second, all four of these civilization centers learned about the amazing discoveries of Babylonian astronomers made during the period of around 900 BCE to 600 BCE. The Babylonian astronomers were the first to accurately record and calculate the regular motions of the planets and the stars. Suddenly a brand new idea detonated in the imagination – the universe is ruled by absolute and invariable law. This idea brought immense changes to every aspect of civilization, from Greece to China. Religions had to adapt and absorb this incredible idea of universal and perfect law. In the Middle East, gods were held responsible for instituting natural laws. In India, the gods upheld dharma. In China, the Tao, the “universal right path” ultimately controls everything. In Greece, natural science was born.
Although naturalism is most often associated with its Western philosophical and scientific tradition, other naturalisms began during the Axial Age as well. Taoism has often been understood as a naturalistic philosophy, since the ultimate power of the Tao is still part of nature. Several important varieties of Buddhism have no beliefs about the afterlife or anything supernatural. The Carvaka school of Hindu philosophy, notable for its defiant materialism and atheism, also dates from this Axial Age. For over 2,600 years, religions in the major centers of civilization have been matched by a powerful alternative that looks to nature alone.
Modern naturalism is primarily indebted to the boldness of Greek rationalism and science. The origins of science come from such theorizing about what nature is made of and how nature works. In this new scientific way of thinking, more complex things are to be explained in terms of simpler things, and fairly unpredictable events are to be explained in terms of more predictable regularities. A religious mode of thinking proceeds in the opposite manner: simpler things are to be explained by more complex things, and regular patterns are explainable by unpredictable events. For example, a religion may say that human beings (simpler) were created by a god (more complex), or that the pattern of the four seasons (fairly regular) was instituted by a divine act (not predictable), or that a moral rule (strictly valid) was ordered by a god’s command (which could have been otherwise). Religious thinking attempts to apply ways we understand each other in our attempts to understand nature around us. Religions are basically about complex and unpredictable events happening at special times to privileged peoples. Such anthropocentric (humanity-centered) reasoning actually is highly unreasonable when applied to the world, since it privileges the human perspective all out of proper proportion to nature. Instead of privileging one perspective, natural science tries to offer explanations that can work from anywhere. Simple things and predictable regularities, valid anywhere in the universe, are precisely what science seeks.
Finding their all-too-human gods unsatisfying, many Greek intellectuals put their confidence in scientific thinking. Greek philosophers, starting with Thales and the Ionian school around 600 BCE, offered speculations about the origin and constitution of the world that left little or no role for gods or spirits. Perhaps everything is made of one of the four basic elements known to the Greeks. One philosopher suggested water, another fire; another proposed that underlying the elements is a more fundamental, formless energy that can become anything. Democritus (c. 400 BCE) declared his radically materialistic view that only tiny atoms and gaps of empty space really exist. Aristotle (c. 350 BCE) catalogued a wide variety of these speculations, and added his own reasoned theories. Skepticism about the gods was more openly discussed. By 100 BCE, sophisticated schools of Greek philosophy argued their merits, and in turn they taught Western civilization, including its Christian component, how to reason.
Today’s naturalism takes advantage of the vast amount of scientific knowledge we now possess. But the naturalistic spirit is far older than experimental science, and traces its birth back to the very origins of reason itself.