Christian doctrines and pluralism
At the heart of Western religious debate about the possible existence of life on other worlds are the key issues of the supposed special relationship between man and God, the incarnation and redemption. Early Christian scholars, having embraced the one-world, geocentric cosmology of Aristotle, generally rejected pluralism. This continued to be the case following the introduction into the West of many previously unavailable classical writings in the 13th century. However, debate did broaden at this time and there were several suggestions that while God actually created only one world, it was in his power to have produced many. Nicholas of Cusa was exceptional, as a high-ranking cleric, in speculating freely upon the possibility of multiple life-bearing worlds, including an inhabited Sun and Moon. William Vorilong was among the first to comment on how this doctrine might be compatible with a belief in Christ's sacrifice and redemption (see medieval philosophy, related to the possibility of extraterrestrial life).
Following the Copernican Revolution, the debate over the theological implications of pluralism intensified. The dawning realization that the Earth was an ordinary planet and that the Sun was just one of many stars, each perhaps with its own retinue of worlds, forced philosophers, theologians, and scientists to confront the possibility that life, including intelligent life, might be common in the Universe. Some continued to reject this view, arguing that Christ's atonement and God's relationship with man were unique and, therefore, that there could be only one inhabited world. Others employed a variety of arguments designed to show that Christianity and pluralism could comfortably coexist (see plenitude, principle of; chain of being, great; microscope argument). These efforts to enlarge the Christian cosmos resulted in the rise of natural theology and the doctrine of the transmigration of souls which reached its most extreme form in the pronouncements of Emmanuel Swedenborg. The debate climaxed in the middle of the 19th century, following publication of the anti-pluralist essay by William Whewell. Thereafter, theological and scientific arguments related to the possibility of extraterrestrial life became increasingly decoupled if not entirely divorced (see SETI, religious dimension).