Worldwide percentage of Adherents by Religion, 2010
The world's principal religions and spiritual traditions may be classified into a small number of major groups, although this is by no means a uniform practice. This theory began in the 18th century with the goal of recognizing the relative levels of civility in societies.
In world cultures, there have traditionally been many different groupings of religious belief. In Indian culture, different religious philosophies were traditionally respected as academic differences in pursuit of the same truth. In Islam, the Quran mentions three different categories: Muslims, the People of the Book, and idol worshipers. Initially, Christians had a simple dichotomy of world beliefs: Christian civility versus foreign heresy or barbarity. In the 18th century, "heresy" was clarified to mean Judaism and Islam; along with paganism, this created a fourfold classification which spawned such works as John Toland's Nazarenus, or Jewish, Gentile, and Mahometan Christianity, which represented the three Abrahamic religions as different "nations" or sects within religion itself, the "true monotheism."
Daniel Defoe described the original definition as follows: "Religion is properly the Worship given to God, but 'tis also applied to the Worship of Idols and false Deities." At the turn of the 19th century, in between 1780 and 1810, the language dramatically changed: instead of "religion" being synonymous with spirituality, authors began using the plural, "religions," to refer to both Christianity and other forms of worship. Therefore, Hannah Adams's early encyclopedia, for example, had its name changed from An Alphabetical Compendium of the Various Sects... to A Dictionary of All Religions and Religious Denominations.
In 1838, the four-way division of Christianity, Judaism, Mahommedanism (archaic terminology for Islam) and Paganism was multiplied considerably by Josiah Conder's Analytical and Comparative View of All Religions Now Extant among Mankind. Conder's work still adhered to the four-way classification, but in his eye for detail he puts together much historical work to create something resembling our modern Western image: he includes Druze, Yezidis, Mandeans, and Elamites under a list of possibly monotheistic groups, and under the final category, of "polytheism and pantheism," he listed Zoroastrianism, "Vedas, Puranas, Tantras, Reformed sects" of India as well as "Brahminical idolatry," Buddhism, Jainism, Sikhism, Lamaism, "religion of China and Japan," and "illiterate superstitions" as others.