The first question to be resolved when discussing atheism is the basic one: what is an atheist?
Atheism is not an organized belief system the way Christianity or Islam is. An atheist can believe any number of things, ranging from the standard "there probably aren't any gods" to "there are no gods" to "god is dead" (this one is purely philosophical, not the literal belief that a god existed, then died) to "humanity is god" (again, generally philosophical) and anything in between.
To begin with something simple, the 1913 edition of Webster's Revised Unabridged Dictionary offers this: "One who disbelieves or denies the existence of a God, or supreme intelligent Being."
Definitions of this kind are generally accepted, bearing in mind that "disbelief" can be interpreted to mean anything from simple lack of belief to active rejection of belief.
In short, someone being an atheist can mean a number of things, so before you ascribe beliefs they do not hold to someone (a good way to piss anyone off...), make sure you're on the same page!
While many people, atheists and religious, see atheism as stemming from scientific developments and blame Darwin's evolutionary theory for its spread, the truth is that what can be generally considered atheism is as old as the hills. There's also the curious etymology of the word and its shift in usage. For a long time in history, atheist was the word used to describe people who believed in other gods
rather than no gods
. In Ancient Greece and Rome, the state supported religion was regarded as the one true and official religion. At the trial of Socrates, the great philosopher was called "atheos" because he did not subscribe to the Gods of the State (that is state recognized religion) and practised private beliefs. Likewise, in a curious irony, early Christians were persecuted by the Romans for being "atheists" as well since they did not subscribe to pagan beliefs. In medieval Europe, Catholics called heretics, Protestants and dissenting priests "atheists" simply because they did not accept official Church doctrine.
In terms of atheism as it means today, that is a system of ethics and philosophy drawn from science and empiricism which is non-supernatural, the Greek Sophists and Atomists were more important. They were the ones who started criticizing Greek myths as merely elaborate fabrications of Kings and Emperors raised to Gods, they also started describing the natural world using language stripped of metaphors. To them Greek myths and its multiple Gods were merely anthropomorphized representations of natural phenomena and fancy metaphors. The philosopher Theodoros of Cyrene even exposed the Elusinian Mystery Cult
and criticized religion as largely a money-making scam in terms that are fairly modern. This more skeptical worldview can also be seen in the plays of Euripides
, roughly contemporary to these changes. He was often accused by critics of lacking in piety, in his plays Gods and Greek Heroes are often depicted in down-to-earth fashion, speaking everyday language as opposed to the more religious plays of Aeschylus and Sophocles. Epicurus inspired by these writers, charted out the first coherent materialist ideology. Although Epicurus acknowledged the existence of Gods, by describing the problem of evil, he stated that if the Gods existed then it was unlikely that human suffering mattered to such beings and that it made little sense organizing life and ethics based on a morality
alien to humanity. He also denied the existence of an afterlife and stressed the importance and vitality of the visible world.
It's also important to note that such skepticism of religion was by no means a Western phenomenon. Buddhism and Jainism for instance was a philosophy without a Deity figure, though other sects approached something resembling monotheism later on. Hinduism had materialist schools such as the Carvaka, Samkhya and Mimamsa. In China, Confucius developed a philosophy of education, curiosity and learning that explicitly distanced itself from metaphysical and spiritual questions noting that such concepts even if it was true was generally available and valuable to the very few, and that society as a whole should be considered with materially improving The Needs of the Many
. Likewise, Charles Darwin in describing his voyages to South America stated that some native tribes did not even have a word for God and organized their society without any identifiable religion (and so can't strictly be labelled atheists since they never believed in God to start with) noting that it refuted the idea that religion or belief was intrinsic or heritable, rather than cultural and acquired. During the Golden Age of the Arab World, several writers such as Omar Khayyam, Averroes, Ibn al-Rawandi, Abu Bakr al-Razi expressed ideas that stressed education, materialism, criticized infallibility of religious truths and expressed a naturalistic worldview that would supersede religious explanations. The free-thinker likewise Al-Maʿarri regarded religion as a "fable invented by the ancients". Even in the Catholic Church, Saint Augustine, a former Manichaen(an African heretical sect) stated that he considered the Bible's fantastic stories to be largely embellished to be accessible to the common man and he dismissed literal interpretations of the Bible's account for creation, noting that as and when science advanced with superior explanations, it should supplant existing Biblical interpretations. This was the defense which Galileo (who was a religious man) used, unsuccessfully, in his trial argument for Heliocentrism.
Modern Atheism first found voice in the course of The Enlightenment
and The French Revolution
, largely as a consequence on the debate of separation between Church and State. It was accompanied by Deism
at first. Philosophers such as Spinoza, Voltaire and Rousseau advocated belief in a distant, immaterial, non-human deity who governed by natural (i.e. scientific) laws. Deism attacked Christian intolerance and superstition, advocated science and democracy. They argued that religion should have no place in politics, that society should be free to discuss different ideas and have total religious tolerance. In the Revolution, graffiti stating "Death is an Eternal Sleep" often defaced churches and cemeteries, Cathedrals and Altar-pieces were subject to petty and creative vandalism, giving free public expression to atheist ideas for the first time in Western history. Inspired by the Revolution, romantic poets like Percy Shelley wrote a pamphlet titled "The Necessity of Atheism" and the idea was common in Romantic, Revolutionary and Decadent circles. Politically and philosophically, Friedrich Nietzsche
noted that with the Revolution, "God is Dead" that is, the all-powerful, idea of God, even among liberal believers, was not the same in an age gradually supplanted by scientific, philosophical and political changes. He noted that the end of Christianity or a single belief as dominating Western culture will lead to a period of nihilism from which people were now free to create their own values and moral code. Charles Darwin's theory of evolution sparked a major change in Victorian England and much later, America, since it provided a scientific explanation for human origins that no longer required a human deity to shape it for human purpose.
It became possible in the dawn of the 20th Century, to live in human society, at least in the Western World, where religion does not play a dominant role and the decline in attendance and social leverage of religion has since then made atheism more and more common.