Developing observations in Europe seemed to show that there were worlds beyond our own Earth. While this was an idea that pre-dated Christianity, the idea that there was only one world – in accordance with Christian teachings – had been supported by the Church. Growing evidence that there must be more worlds damaged the credibility of the Church, and all ancient knowledge, including Biblical “truth.”

Cosmic pluralism, the plurality of worlds, or simply pluralism, describes the philosophical belief in numerous “worlds” in addition to Earth (possibly an infinite number), which may harbour extraterrestrial life.

The debate over pluralism began as early as the time of Anaximander (c. 610 – c. 546 BC) as an abstract metaphysical argument, long predating the scientific Copernican conception that the Earth is one of numerous planets. It has continued, in a variety of forms, until the modern era.

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The telescope appeared to prove that a multitude of life was reasonable and an expression of God’s creative omnipotence; still powerful theological opponents, meanwhile, continued to insist that although the Earth may have been displaced from the center of the cosmos, it was still the unique focus of God’s creation. Thinkers such as Johannes Kepler were willing to admit the possibility of pluralism without truly supporting it.

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Cosmic pluralism was a corollary to notions of infinity and the purported multitude of life-bearing worlds were more akin to parallel universes (either contemporaneously in space or infinitely recurring in time) than to different solar systems. After Thales and his student Anaximander opened the door to an infinite universe, a strong pluralist stance was adopted by the atomists, notably Leucippus, Democritus, and Epicurus. While these were prominent thinkers, their opponents—Plato and Aristotle—had greater effect. They argued that the Earth is unique and that there can be no other systems of worlds.This stance neatly dovetailed with later Christian ideas and pluralism was effectively suppressed for approximately a millennium.

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Deism is a theological/philosophical position that combines the rejection of revelation and authority as a source of religious knowledge with the conclusion that reason and observation of the natural world are sufficient to determine the existence of a single creator of the universe.
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While many believe the United States to be founded as a Christian society, many of the leaders of the American revolution were actually influenced by deism. Benjamin Franklin, Ethan Allen, George Washington, James Madison, Thomas Jefferson, and Thomas Paine are all identified as deists.

An ancient Greek and Christianity-influenced 17th-century Europe Humanist Enlightenment era faith of nature, reason, and free-thought, Deists rejected the unreliable word of man, including the miracles and supernaturalism of the Judeo-Christian tradition in favour of their own relationship with God.