Liberal Christianity

Liberal Christianity, also known as liberal theology, is a movement that interprets and reforms Christian teaching by taking into consideration modern knowledge, science and ethics. It emphasizes the importance of reason and experience over doctrinal authority. Liberal Christians view their theology as an alternative to both atheistic rationalism and theologies based on traditional interpretations of external authority (such as the Bible or sacred tradition).
Liberal theology grew out of Enlightenment rationalism and romanticism of the 18th and 19th centuries. By the late 19th and early 20th centuries, it was characterized by an acceptance of Darwinian evolution, a utilization of modern biblical criticism and participation in the Social Gospel movement. This was also the period when liberal theology was most dominant within the Protestant churches. Liberal theology's influence declined with the rise of neo-orthodoxy in the 1930s and with liberation theology in the 1960s. Catholic forms of liberal theology emerged in the late 19th century. By the 21st century, liberal Christianity had become an ecumenical tradition, including both Protestants and Catholics. 
In the context of theology, the word "liberal" does not refer to political liberalism, and it should be distinguished from progressive Christianity. Historically, liberal Christianity has also been referred to as Christian modernism (see Catholic modernism and Fundamentalist–Modernist controversy).
Liberal Protestantism.
Liberal Protestantism developed in the 19th century out of a need to adapt Christianity to a modern intellectual context. With the acceptance of Charles Darwin's theory of natural selection, some traditional Christian beliefs, such as parts of the Genesis creation narrative, became difficult to defend. Unable to ground faith exclusively in an appeal to scripture or the person of Jesus Christ, liberals, according to theologian and intellectual historian Alister McGrath, "sought to anchor that faith in common human experience, and interpret it in ways that made sense within the modern worldview." Beginning in Germany, liberal theology was influenced by several strands of thought, including the Enlightenment's high view of human reason and Pietism's emphasis on religious experience and interdenominational tolerance.
The sources of religious authority recognized by liberal Protestants differed from conservative Protestants. Traditional Protestants understood the Bible to be uniquely authoritative ("sola scriptura"); all doctrine, teaching and the church itself derive authority from it. A traditional Protestant could therefore affirm that "what Scripture says, God says." Liberals, however, seek to understand the Bible through modern biblical criticism, such as historical criticism, that began to be used in the late 1700s to ask if biblical accounts were based on older texts or whether the Gospels recorded the actual words of Jesus. The use of these methods of biblical interpretation led liberals to conclude that "none of the New Testament writings can be said to be apostolic in the sense in which it has been traditionally held to be so". This conclusion made "sola scriptura" an untenable position. In its place, liberals identified the historical Jesus as the "real canon of the Christian church". 
The two groups also disagreed on the role of experience in confirming truth claims. Traditional Protestants believed scripture and revelation always confirmed human experience and reason. For liberal Protestants, there were two ultimate sources of religious authority: the Christian experience of God as revealed in Jesus Christ and universal human experience. In other words, only an appeal to common human reason and experience could confirm the truth claims of Christianity. 
Liberals abandoned or reinterpreted traditional doctrines in light of recent knowledge. For example, the traditional doctrine of original sin was rejected for being derived from Augustine of Hippo, whose views on the New Testament were believed to have been distorted by his involvement with Manichaeism. Christology was also reinterpreted. Liberals stressed Christ's humanity, and his divinity became "an affirmation of Jesus exemplifying qualities which humanity as a whole could hope to emulate". Liberal Christians sought to elevate Jesus' humane teachings as a standard for a world civilization freed from cultic traditions and traces of traditionally pagan types of belief in the supernatural.
As a result, liberal Christians placed less emphasis on miraculous events associated with the life of Jesus than on his teachings. The effort to remove "superstitious" elements from Christian faith dates to intellectually reforming Renaissance Christians such as Erasmus (who compiled the first modern Greek New Testament) in the late 15th and early-to-mid 16th centuries, and, later, the natural-religion view of the Deists, which disavowed any revealed religion or active interaction between the Creator and the creation, in the 17–18th centuries. The debate over whether a belief in miracles was mere superstition or essential to accepting the divinity of Christ constituted a crisis within the 19th-century church, for which theological compromises were sought. Many liberals prefer to read Jesus' miracles as metaphorical narratives for understanding the power of God. Not all theologians with liberal inclinations reject the possibility of miracles, but many reject the polemicism that denial or affirmation entails.
Nineteenth-century liberalism had an optimism about the future in which humanity would continue to achieve greater progress. This optimistic view of history was sometimes interpreted as building the kingdom of God in the world.
Theologians.
Reformed theologian Friedrich Schleiermacher (1768–1834) is often considered the father of liberal Protestantism. In response to Romanticism's disillusionment with Enlightenment rationalism, Schleiermacher argued that God could only be experienced through feeling, not reason. In Schleiermacher's theology, religion is a feeling of absolute dependence on God. Humanity is conscious of its own sin and its need of redemption, which can only be accomplished by Jesus Christ. For Schleiermacher, faith is experienced within a faith community, never in isolation. This meant that theology always reflects a particular religious context, which has opened Schleirmacher to charges of relativism.
Albrecht Ritschl (1822–1889) disagreed with Schleiermacher's emphasis on feeling. He thought that religious belief should be based on history, specifically the historical events of the New Testament. When studied as history without regard to miraculous events, Ritschl believed the New Testament affirmed Jesus' divine mission. He rejected doctrines such as the virgin birth of Jesus and the Trinity. The Christian life for Ritschl was devoted to ethical activity and development, so he understood doctrines to be value judgments rather than assertions of facts. Influenced by the philosophy of Immanuel Kant, Ritschl viewed "religion as the triumph of the spirit (or moral agent) over humanity’s natural origins and environment." Ritschl's ideas would be taken up by others, and Ritschlianism would remain an important theological school within German Protestantism until World War I. Prominent followers of Ritschl include Wilhelm Herrmann, Julius Kaftan and Adolf von Harnack.
Liberal Catholicism.
Catholic forms of theological liberalism have existed since the 19th century in England, France and Italy. In the late 19th and early 20th centuries, a liberal theological movement developed within the Catholic Church known as Catholic modernism. Like liberal Protestantism, Catholic modernism was an attempt to bring Catholicism in line with the Enlightenment. Modernist theologians approved of radical biblical criticism and were willing to question traditional Christian doctrines, especially Christology. They also emphasized the ethical aspects of Christianity over its theological ones. Important modernist writers include Alfred Loisy and George Tyrrell. Modernism was condemned as heretical by the leadership of the Catholic Church.
Papal condemnation of modernism and Americanism slowed the development of a liberal Catholic tradition in the United States. Since the Second Vatican Council, however, liberal theology has experienced a resurgence. Liberal Catholic theologians include David Tracy and Francis Schussler Fiorenza.
Influence in the United States.
Liberal Christianity was most influential with Mainline Protestant churches in the early 20th century, when proponents believed the changes it would bring would be the future of the Christian church. Its greatest and most influential manifestation was the Christian Social Gospel, whose most influential spokesman was the American Baptist Walter Rauschenbusch. Rauschenbusch identified four institutionalized spiritual evils in American culture (which he identified as traits of "supra-personal entities", organizations capable of having moral agency): these were individualism, capitalism, nationalism and militarism.
Other subsequent theological movements within the U.S. Protestant mainline included political liberation theology, philosophical forms of postmodern Christianity, and such diverse theological influences as Christian existentialism (originating with Søren Kierkegaard and including other theologians and scholars such as Rudolf Bultmann and Paul Tillich) and even conservative movements such as neo-evangelicalism, neo-orthodoxy, and paleo-orthodoxy. Dean M. Kelley, a liberal sociologist, was commissioned in the early 1970s to study the problem, and he identified a potential reason for the decline of the liberal churches: what was seen by some as excessive politicization of the Gospel, and especially their apparent tying of the Gospel with Left-Democrat/progressive political causes.
The 1990s and 2000s saw a resurgence of non-doctrinal, theological work on biblical exegesis and theology, exemplified by figures such as Marcus Borg, John Dominic Crossan, John Shelby Spong, Karen Armstrong and Scotty McLennan.