Stirrings of religious rationalism were already felt in the Middle Ages regarding the Christian revelation. Thus, the skeptical mind of Peter Abelard (10791142) raised doubts by showing in his Sic et non (Yes and No) many contradictions among beliefs handed down as revealed truths by the Church Fathers. Aquinas, the greatest of the medieval thinkers, was a rationalist in the sense of believing that the larger part of revealed truth was intelligible to and demonstrable by reason, though he thought that a number of dogmas opaque to reason must be accepted on authority alone.

Religious rationalism did not come into its own, however, until the 16th and 17th centuries, when it took two chief forms: the scientific and the philosophical.

Galileo was a pioneer in astronomy and the founder of modern dynamics. He conceived of nature as governed throughout by laws statable with mathematical precision; the book of nature, he said, is written in mathematical form. This notion not only ruled out the occasional appeal to miracle; it also collided with dogmas regarding the permanent structure of the worldin particular with that which viewed the Earth as the motionless centre of the universe. When Galileos demonstration that the Earth moves around the Sun was confirmed by the work of Sir Isaac Newton (16421727) and others, a battle was won that marked a turning point in the history of rationalism, since it provided a decisive victory in a crucial case of conflict between reason and apparently revealed truth.

The rationalism of Descartes, as already shown, was the outcome of philosophical doubt rather than of scientific inquiry. The self-evidence of the cogito, seen by his natural light, he made the ideal for all other knowledge. The uneasiness that the church soon felt in the face of such a test was not unfounded, for Descartes was in effect exalting the natural light into the supreme court even in the field of religion. He argued that the guarantee against the possibility that even this natural light might be deceptive lay in the goodness of the Creator. But then to prove this Creator, he had to assume the prior validity of the natural light itself. Logically, therefore, the last word lay with rational insight, not with any outside divine warrant (see Cartesian circle). Descartes was inadvertently beginning a Copernican revolution in theology. Before his time, the truths regarded as most certain were those accepted from revelation; afterward these truths were subject to the judgment of human reason, thus breaking the hold of authority on the European mind.

The rationalist attitude quickly spread, its advance forming several waves of general interest and influence. The first wave occurred in England in the form of Deism. Deists accepted the existence of God but spurned supernatural revelation. The earliest member of this school, Lord Herbert of Cherbury (15831648), held that a just God would not reveal himself to a part of his creation only and that the true religion is thus a universal one, which achieves its knowledge of God through common reason. The Deistic philosopher John Toland (16701722), in his Christianity Not Mysterious (1696), sought to show that there is nothing in the Gospels contrary to reason, nor above it; any doctrine that is really above reason would be meaningless to humans. Attacking revelation, the freethinking polemicist Anthony Collins (16761729) maintained that the prophecies of the Hebrew Bible (Old Testament) failed of fulfillment; and the religious controversialist Thomas Woolston (16701733) urged that the New Testament miracles, as recorded, are incredible. Matthew Tindal (16571733), most learned of the English Deists, argued that the essential part of Christianity is its ethics, which, being clearly apparent to natural reason, leaves revelation superfluous. Thus the Deists, professing for the most part to be religious themselves, did much to reconcile their public to the free play of ideas in religion.

The second wave of religious rationalism, less moderate in tone and consequences, was French. This wave, reflecting an engagement with the problem of natural evil, involved a decay in the natural theology of Deism such that it merged eventually with the stream that led to materialistic atheism. Its moving spirit was Voltaire (16941778), who had been impressed by some of the Deists during a stay in England. Like them, he thought that a rational person would believe in God but not in supernatural inspiration. Hardly a profound philosopher, he was a brilliant journalist, clever and humorous in argument, devastating in satire, and warm in human sympathies. In his Candide and in many other writings, he poured irreverent ridicule on the Christian scheme of salvation as incoherent and on the church hierarchy as cruel and oppressive. In these attitudes he had the support of Denis Diderot (171384), editor of the most widely read encyclopaedia that had appeared in Europe. The rationalism of these thinkers and their followers, directed against both the religious and the political traditions of their time, did much to prepare the ground for the explosive French Revolution.

The next wave of religious rationalism occurred in Germany under the influence of Hegel, who held that a religious creed is a halfway house on the road to a mature philosophy, the product of a reason that is still under the sway of feeling and imagination. This idea was taken up and applied with learning and acuteness to the origins of Christianity by David Friedrich Strauss (180874), who published in 1835, at the age of 27, a remarkable and influential three-volume work, Das Leben Jesu (The Life of Jesus, Critically Examined, 1846). Relying largely on internal inconsistencies in the Synoptic Gospels, Strauss undertook to prove these books to be unacceptable as revelation and unsatisfactory as history. He then sought to show how an imaginative people innocent of either history or science, convinced that a messiah would appear, and deeply moved by a unique moral genius, inevitably wove myths about his birth and death, his miracles, and his divine communings.

Strausss thought as it affected religion was continued by the philosophical historian Ernest Renan (182392) and as it affected philosophy by the humanist Ludwig Feuerbach (180472) of the Hegelian left. Renans Vie de Jsus (1863; Life of Jesus) did for France what Strausss book had done for Germany, though the two differed greatly in character. Whereas Strausss work had been an intellectual exercise in destructive criticism, Renans was an attempt to reconstruct the mind of Jesus as a wholly human persona feat of imagination, performed with a disarming admiration and even reverence for its subject and with a felicity of style that gave it a large and lasting audience. Feuerbachs Wesen des Christentums (1841; Essence of Christianity) applied the myth theory even to belief in the existence of God, holding that man makes God in his own image.

The fourth wave occurred in Victorian England, following the publication in 1859 of Origin of Species by Charles Darwin (180982). This book was taken as a challenge to the authority of Scripture because there was a clear inconsistency between the Genesis account of creation and the biological account of humans slow emergence from lower forms of life. The battle raged with bitterness for several decades but died away as the theory of evolution gained more general acceptance.

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Rationalism - Religious rationalism | Britannica