The origins of the word infidel date to the late 15th century, deriving from the French infidèle or Latin īnfidēlis, from in- "not" + fidēlis "faithful" (from fidēs "faith", related to fīdere 'to trust'). The word originally denoted a person of a religion other than one's own, specifically a Christian to a Muslim, a Muslim to a Christian, or a Goy to a Jew. Later meanings in the 15th century include "unbelieving", "a non-Christian" and "one who does not believe in religion" (1527).
Christians have historically referred to people outside their religious group as infidels, somebody who has actively rejected the Christian religion. It only became a well established notion in English sometime in the early sixteenth century, when Jews or "Mohammedans"(Muslims), were described as active opponents to Christianity, and as such infidel was seen as term of contempt. In Catholic doctrine, an infidel is one who does not believe in the doctrine at all and is thus distinct from a heretic, who is one seen as having fallen astray from true doctrine, i.e. by denying the divinity of Jesus. Similarly, the ecclesiastical term was also used by the Methodist Church, in reference to those "without faith".
Today, the usage of the term infidel has declined; the current preference is for the terms non-Christians and non-believers (persons without religious affiliations or beliefs), reflecting the commitment of mainstream Christian denominations to engage in dialog with persons of other faiths. Nevertheless, some apologists have argued for the usage of the term, stating that it does not come from a disrespectful perspective, but is similar to using the term orthodox for devout believers.
Moreover, some translations of the Bible, such as the Authorized Version, which is still in vogue today, employ the word infidel, while others supplant the term with nonbeliever; the term is found in two places:
And what concord hath Christ with Belial? Or what part hath he that believeth with an infidel? —2 Corinthians 6:15 KJV
But if any provide not for his own, and specially for those of his own house, he hath denied the faith, and is worse than an infidel. —1 Timothy 5:8 KJV
Infidel is an English language word equivalent to the Arabic word for non-Muslims, kafir (sometimes "kaafir", "kufr" or "kuffar"), and the Turkish loanword gâvur, literally the one who "covers" and "conceals". The term is sometimes used in Islamic literature synonymously with mushrik (also translated as "polytheist").
In the Quran the term kafir is first applied to the unbelieving Meccans, and their attempts to refute and revile Muhammad. Later Muslims are ordered to keep apart from them, defend themselves from their attacks, and finally take the offensive against them. In some verses, particularly those recited after the Hijra in 622 AD, the concept of kafir was expanded upon, with Jews and Christians included. The expanded term kafir refers to anyone who disbelieves in the religion of Islam, who does not pray the obligatory 5 prayers a day, the one that mocks the religion of Islam, the one that sets up intermediates between him and God, who does not regard the kafiroon as kaffirs, whoever believes one's teaching is more reliable and trustworthy than the Prophet Muhammad's (saw) teachings, whoever hates something of the Prophet, whoever practices witchcraft, and whoever supports the kaffirs against the Muslims (in terms of war, harming, etc.). Jews were condemned as kafirs for their disbelief in God's ayah, Christians were condemned as kafirs for their belief in the Trinity, which the Qur'an declared as major kufr (disbelief) (kufr akbar), which puts one outside of the pale of Islam (Surah al-Maa’idah - 5:116 for example).
The corpus of hadith deals with the fate of the kafir in the afterlife and reflects a major controversy in early Islam as to whether a Muslim should be considered a kafir for committing a major sin. Some hadiths prohibit declaring a Muslim to be a kafir, but the term was nonetheless fairly frequent in the internal religious polemics of the age.
Some texts of Sunni sect of Islam include other sects of Islam such as Shia as infidel. Certain sects of Islam, such as Wahhabism, include as kafir those Muslims who undertake Sufi shrine pilgrimage and follow Shia teachings about Imams. Similarly, in Africa and South Asia, certain sects of Islam such as Hausas, Ahmadi, Akhbaris have been repeatedly declared as Kufir or infidels by other sects of Muslims.
In the Quran the term "people of the book" refers to Jews, Christians, and Sabians. Some scholars claim Islam considers Jews and Christians as fellow believers. They are called the "People of the Book (Ahl al-kitab)". Other Islamic scholars and literature, however, consider Jews and Christians as kafirs. The class of kafir also includes the category of murtadd, variously translated as apostate or renegades, for whom classical jurisprudence prescribes death if they refuse to return to Islam. On the subject of ritual impurity of unbelievers, one finds a range of opinions, "from the strictest to the most tolerant", in classical jurisprudence.
Historically, the attitude toward unbelievers in Islam was determined more by socio-political conditions than by religious doctrine. A tolerance toward unbelievers "impossible to imagine in contemporary Christendom" prevailed even to the time of the Crusades, particularly with respect to the People of the Book. However, animosity was nourished by repeated wars with unbelievers, and warfare between Safavid Persia and Ottoman Turkey brought about application of the term kafir even to Persians in Turkish fatwas.
Like, "infidel", the term kafir has developed into a term of abuse. "In theory" a Muslim commits a punishable offense if he says to a Christian or a Jew: "thou unbeliever".
In Sufism the term underwent a special development, as in a well-known verse of Abu Sa'id: "So long as belief and unbelief are not perfectly equal, no man can be a true Muslim", which has prompted various explanations.
Judaism has a notion of pagan gentiles who are called acum (an acronym of Ovdei Cohavim u-Mazzaloth or, literally, those who are "star-and-constellation worshippers") or idolaters. However, the Hebrew term, kofer, cognate with the Arabic kafir, is reserved only for apostate Jews.
In Quid super his, Innocent IV, asked the question "[I]s it licit to invade a land that infidels possess or which belongs to them?" and held that while Infidels had a right to dominium (right to rule themselves and choose their own governments), however the pope, as the Vicar of Christ, de jure possessed the care of their souls and had the right to politically intervene in their affairs if their ruler violated or allowed his subjects to violate a Christian and Euro-centric normative conception of Natural law, such as sexual perversion or idolatry. He also held that he had an obligation to send missionaries to infidel lands, and that if they were prevented from entering or preaching, then the pope was justified in dispatching Christian forces accompanied with missionaries to invade those lands, as Innocent stated simply "If the infidels do not obey, they ought to be compelled by the secular arm and war may be declared upon them by the pope, and nobody else." This was however not a reciprocal right and non-Christian missionaries such as those of Muslims could not be allowed to preach in Europe "because they are in error and we are on a righteous path."
A long line of Papal hierocratic canonists, most notably those who adhered to Alanus Anglicus's influential arguments of the Crusading-era, denied Infidel dominium, and asserted Rome's universal jurisdictional authority over the earth, and the right to authorize pagan conquests solely on the basis of non-belief because of their rejection of the Christian god. In the extreme hierocractic canonical discourse of the mid-twelfth century such as that espoused by Bernard of Clairvaux, the mystic leader of the Cisertcians, legitimized German colonial expansion and practice of forceful Christianisation in the Slavic territories as a holy war against the Wends, arguing that infidels should be killed wherever they posed a menace to Christians. When Frederick the II unilaterally arrogated papal authority, he took on the mantle to "destroy convert, and subjugate all barbarian nations." A power in papal doctrine reserved for the pope. Hostiensis, a student of Innocent, in accord with Alanus, also asserted "... by law infidels should be subject to the faithful." and the heretical quasi-Donatist John Wyclif, regarded as the forefather of English Reformation, also held that valid dominium rested on a state of grace.
The Teutonic Knights were one of the by-products of this papal hierocratic and German discourse. After the Crusades in the Levant, they moved to crusading activities in the infidel Baltics. Their crusades against the Lithuanians and Poles however precipitated the Lithuanian Controversy, and the Council of Constance, following the condemnation of Wyclif, found Hostiensis's views no longer acceptable and ruled against the knights. Future Church doctrine was then firmly aligned with Innocents IV's position.
The development of counter arguments later on the validity of Papal authority, the rights of infidels and the primacy of natural law, led to various treatises such as those by Hugo Grotius, John Locke, Immanuel Kant and Thomas Hobbes, which in turn led to the transformation of international law's treatment of the relationship between Christian and non-Christian societies and the development of human rights.
During the Age of discovery, the Papal Bulls such as Romanus Pontifex and more importantly inter caetera (1493), implicitly removed dominium from infidels and granted them to the Spanish Empire and Portugal with the charter of guaranteeing the safety of missionaries. Subsequent English and French rejections of the bull refuted the Popes authority to exclude other Christian princes. As independent authorities such as the Head of the Church of England, they drew up charters for their own colonial missions based on the temporal right for care of infidel souls in language echoing the inter caetera. The charters and papal bulls would form the legal basis of future negotiations and consideration of claims as title deeds in the emerging Law of nations in the European colonization of the Americas.
The rights bestowed by Romanus Pontifex and inter caetera have never fallen from use, serving as the basis for legal arguments over the centuries. The U.S. Supreme Court ruled in the 1823 case Johnson v. M'Intosh that as a result of European discovery and assumption of ultimate dominion, Native Americans had only a right to occupancy of native lands, not the right of title. This decision was upheld in the 1831 case Cherokee Nation v. Georgia, giving Georgia authority to extend state laws over Cherokees within the state, and famously describing Native American tribes as "domestic dependent nations." This decision was modified in Worcester v. Georgia, which stated that the U.S. federal government, and not individual states, had authority in Indian affairs, but it maintained the loss of right to title upon discovery by Europeans.
Native American groups including the Taíno and Onondaga have called on the Vatican to revoke the bulls of 1452, 1453, and 1493.
According to the Catholic Encyclopedia, the Church views Marriage as forbidden and null when conducted between the faithful (Christians) and infidels, unless a dispensation has been granted. This is because marriage is a sacrament of the Catholic Church, which infidels are deemed incapable of receiving.
Some philosophers such as Thomas Paine, David Hume, George Holyoake, Charles Bradlaugh, Voltaire and Rousseau earned the label of infidel or freethinkers, both personally and for their respective traditions of thought because of their attacks on religion and opposition to the Church. They established and participated in a distinctly labeled, infidel movement or tradition of thought, that sought to reform their societies which were steeped in Christian thought, practice, laws and culture. The Infidel tradition was distinct from parallel anti-Christian, sceptic or deist movements, in that it was anti-theistic and also synonymous with atheism. These traditions also sought to set up various independent model communities, as well as societies, whose traditions then gave rise to various other socio-political movements such as secularism in 1851, as well as developing close philosophical ties to some contemporary political movements such as socialism and the French Revolution.
Towards the early twentieth century, these movements sought to move away from the tag "infidel" because of its associate negative connotation in Christian thought, and is attributed to George Holyoake's coining the term 'secularism' in an attempt to bridge the gap with other theist and Christian liberal reform movements.
In 1793, Immanuel Kant's Religion within the Boundaries of Mere Reason, reflected the Enlightenment periods' philosophical development, one which differentiated between the moral and rational and substituted rational/irrational for the original true believer/infidel distinction.
Laws passed by the Catholic Church governed not just the laws between Christians and Infidels in matters of religious affairs, but also civil affairs. They were prohibited from participating or aiding in infidel religious rites, such as circumcisions or wearing images of non-Christian religious significance.
In the Early Middle Ages, based on the idea of the superiority of Christians to infidels, regulations came into place such as those forbidding Jews from possessing Christian slaves; the laws of the decretals further forbade Christians from entering the service of Jews, for Christian women to act as their nurses or midwives; forbidding Christians from employing Jewish physicians when ill; restricting Jews to definite quarters of the towns into which they were admitted and to wear a dress by which they might be recognized.
Later during the Victorian era, testimony of either self declared, or those accused of being Infidels or Atheists, was not accepted in a court of law because it was felt that they had no moral imperative to not lie under oath because they did not believe in God, or Heaven and Hell.
These rules have now given way to modern legislation and Catholics, in civil life, are no longer governed by ecclesiastical law.