Islam was the dominant religion by far in Indonesia, with the greatest number of religious adherents: around 143 million people or 86.9 percent of the population in 1985, which when adjusted for 1992 estimates represents between 160 million and 170 million adherents. This high percentage of Muslims made Indonesia the largest Islamic country in the world in the early 1990s. Within the nation, most provinces and islands had majority populations of Islamic adherents (ranging from just above 50 percent in Kalimantan Barat and Maluku provinces to as much as 97.8 percent in the Special Region of Aceh).
According to orthodox practice, Islam is a strictly monotheistic religion in which God (Allah or Tuhan) is a pervasive, if somewhat distant, figure. The Prophet Muhammad is not deified, but is regarded as a human who was selected by God to spread the word to others through the Quran, Islam's holiest book, the revealed word of God. Islam is a religion based on high moral principles, and an important part of being a Muslim is commitment to these principles. Islamic law (sharia; in Indonesian, syariah) is based on the Quran; the sunna, Islamic tradition, which includes the hadith (hadis in Indonesian), the actions and sayings of Muhammad; ijma, the consensus of a local group of Islamic jurisprudents and, sometimes, the whole Muslim community; and qiyas or reasoning through analogy. Islam is universalist, and, in theory, there are no national, racial, or ethnic criteria for conversion. The major branches of Islam are those adhered to by the Sunni and Shia Muslims.
To a significant degree, the striking variations in the practice and interpretation of Islam--in a much less austere form than that practiced in the Middle East--in various parts of Indonesia reflect its complex history. Introduced piecemeal by various traders and wandering mystics from India, Islam first gained a foothold between the twelfth and fifteenth centuries in coastal regions of Sumatra, northern Java, and Kalimantan. Islam probably came to these regions in the form of mystical Sufi tradition. Sufism easily gained local acceptance and became synthesized with local customs. The introduction of Islam to the islands was not always peaceful, however. As Islamized port towns undermined the waning power of the East Javanese HinduBuddhist Majapahit kingdom in the sixteenth century, Javanese elites fled to Bali, where over 2.5 million people kept their own version of Hinduism alive. Unlike coastal Sumatra, where Islam was adopted by elites and masses alike, partly as a way to counter the economic and political power of the Hindu-Buddhist kingdoms, in the interior of Java the elites only gradually accepted Islam, and then only as a formal legal and religious context for Javanese spiritual culture.
These historical processes gave rise to enduring tensions between orthodox Muslims and more syncretistic, locally based religion--tensions that were still visible in the early 1990s. On Java, for instance, this tension was expressed in a contrast between santri and abangan, an indigenous blend of native and Hindu-Buddhist beliefs with Islamic practices sometimes also called Javanism, kejawen, agama Jawa, or kebatinan. The terms and precise nature of this opposition were still in dispute in the early 1990s, but on Java santri not only referred to a person who was consciously and exclusively Muslim, santri also described persons who had removed themselves from the secular world to concentrate on devotional activities in Islamic schools called pesantren--literally the place of the santri.
In contrast to the Mecca-oriented philosophy of most santri, there was the current of kebatinan, which is an amalgam of animism, Hindu-Buddhist, and Islamic--especially Sufi--beliefs. This loosely organized current of thought and practice, was legitimized in the 1945 constitution and, in 1973, when it was recognized as one of the agama, President Suharto counted himself as one of its adherents. Kebatinan is generally characterized as mystical, and some varieties were concerned with spiritual self-control. Although there were many varieties circulating in 1992, kebatinan often implies pantheistic worship because it encourages sacrifices and devotions to local and ancestral spirits. These spirits are believed to inhabit natural objects, human beings, artifacts, and grave sites of important wali (Muslim saints). Illness and other misfortunes are traced to such spirits, and if sacrifices or pilgrimages fail to placate angry deities, the advice of a dukun or healer is sought. Kebatinan, while it connotes a turning away from the militant universalism of orthodox Islam, moves toward a more internalized universalism. In this way, kebatinan moves toward eliminating the distinction between the universal and the local, the communal and the individual.
Another important tension dividing Indonesian Muslims was the conflict between traditionalism and modernism. The nature of these differences was complex, confusing, and a matter of considerable debate in the early 1990s, but traditionalists generally rejected the modernists' interest in absorbing educational and organizational principles from the West. Specifically, traditionalists were suspicious of modernists' support of the urban madrasa, a reformist school that included the teaching of secular topics. The modernists' goal of taking Islam out of the pesantren and carrying it to the people was opposed by the traditionalists because it threatened to undermine the authority of the kyai (religious leaders). Traditionalists also sought, unsuccessfully, to add a clause to the first tenet of the Pancasila state ideology requiring that, in effect, all Muslims adhere to the sharia. On the other hand, modernists accused traditionalists of escapist unrealism in the face of change; some even hinted that santri harbored greater loyalty towards the ummah (congregation of believers) of Islam than to the secular Indonesian state.
Despite these differences, the traditionalist Nahdlatul Ulama (literally, Revival of the Religious Scholars, also known as the Muslim Scholars' League), the progressive Consultative Council of Indonesian Muslims (Masyumi), and two other parties were forcibly streamlined into a single Islamic political party in 1973--the Unity Development Party (PPP). Such cleavages may have weakened Islam as an organized political entity, as demonstrated by the withdrawal of the Nahdlatul Ulama from active political competition, but as a popular religious force Islam showed signs of good health and a capacity to frame national debates in the 1990s.