Rationalism, as 'a system of belief regulated by reason,' might be expected to mean the opposite of irrationality, crass ignorance, and perverse prejudice; and the growth of rationalism would then mean the progress of civilisation, the development of the intellectual and moral nature of men and nations. It is nearly in this sense that Lecky uses the word; attributing to its wholesome influence the decay of the belief in magic, witchcraft, and other hideous superstitions, and the substitution of a kindly tolerance in place of blind zeal for persecution.
But in ordinary English usage, general as well as theological, the connotation of the word is substantially different. It is generally employed as a term of reproach for those who, without niterly denying or attempting to overthrow the foundations of religion, make such concessions to the enemy as tend to subvert the faith; who admit the thin end of a wedge that pressed home will rend and destroy the fabric. They rely, more or less exclusively and blameworthy, on mere human reason instead of simply, frankly, and fully accepting the dicta of the divine word. An atheist would not be spoken of as a rationalist, nor would an irreligious, blaspheming freethinker. Rationalists in ordinary parlance are those who are more 'liberal' or 'advanced' than the main body of the orthodox; in especial those who take a 'low' view of inspiration, and minimise or explain away the miraculous details of the history of revelation and redemption. Rationalism is not so much a body of doctrine as a mood of mind, a tendency of thought shown in the attempt to apply to religious doctrine, the sacred story, and the sacred scriptures the same methods of research and proof as are used in mere human science and history, and the literatures of all times and peoples. This feature is also recognised, though with approval, by Lecky in his wider use of the word: 'Rationalism,' he says, 'leads men on all occasions to subordinate dogmatic theology to the dictates of reason and conscience. . . . It predisposes men in history to attribute all kinds of phenomena to natural rather than to miraculous causes; in theology to esteem succeeding religious systems the expression of the wants and aspirations of that religious sentiment which is implanted in man; and in ethics to regard as duties only those which conscience reveals to be such.' Rationalism, not being a system but a temper or drift of mind, has different aims at different times; just as 'liberalism' in politics was not the same thing before 1832 as it came to be after, or in 1832 what it was in 1867, 1885, or 1890. Opinions are heard in sermons and expounded in books by theological professors in 1891 without proving serious stumbling-blocks to the majority, which in 1860 would by all but a small minority have been regarded as distinctly rationalistic. Thus, till lately it was alarming rationalism to dispute the Mosaic authorship of Genesis, the Solomonic authorship of the Song of Songs, and the Davidic authorship of any of the Psalms; now the newer view is assumed by many orthodox teachers. And in the last quarter of the 19th century scholars earnestly support views which they themselves treated as highly dangerous twenty or thirty years earlier. Rationalism of this kind is a transition stage, but not necessarily a transition to unbelief.
The rationalistic temper may be traced in almost every age of the church's history: no doubt the extremers representatives of the Petrine party in sub-apostolic times regarded Paul's views as lax and rationalistic. If the Reformation was not rooted in rationalism (as to Catholics it seems to have been), many of the contentions of the reformers were such as all rationalists accept and sympathise with. Zwingli was a rationalist to Luther and the Lutherans; Socinus was of course a rationalist of an extreme type. The dry and barren dogmatic orthodoxy of Germany in the 17th century fostered a rationalism as cold and unspiritual. In the England of the 18th century, during the Deistic controversies, the Evangelicals of Germany thought, not altogether unjustly, that some of the most conspicuous opponents of the deists were not themselves free from the charge of rationalism; and the Evangelicals of Scotland regarded the 'moderates' of the 18th century, however orthodox in dogma, as thoroughly rationalistic in spirit. Rationalism is not so much opposed to orthodoxy as to mysticism, and what was called variously fanaticism, enthusiasm, 'high-flying,' and methodism. A soulless orthodoxy has not seldom been opposed by a fervent piety that by a not unnatural antithesis has tended to run into heretical extremes; while, on the other hand, actual rationalists have often been foremost amongst the champions of religion, and of revealed religion, against radical freethinking, deism, naturalism, and materialism.
In Germany the term rationalism is more definite in its reference than in England, but is not always used in quite the same sense. The two defective and mutually opposed schools of thought that Kant sought to supersede by his critical philosophy were, on the one hand, a shallow empiricism, and on the other a baseless and overweening metaphysical dogmatism or rationalism. Bacon also contrasted empirical philosophers with rationalists who spin their systems as spiders do cobwebs out of their own bowels. Wolff presents the most conspicuous example of the philosophical rationalism which held that all that is in heaven above and earth beneath could be 'proved' by pseudo-mathematical methods: and as God, responsibility, and immortality were amongst the things that could be proved at endless length and in various ways, this philosophical rationalism led directly up to a rationalist theology, which consisted mainly in a series of dogmas to be demonstrated from the philosophical axioms, including some at least of the doctrines of revealed religion. What in revelation could not be demonstrated according to this scheme was disallowed or explained away. Practical religion became in the Aufklärung a system of mere utilitarian morals.
Kant prepared the way for a deeper view of man, history, and the universe; but his own explicit statements on positive religion were pronouncedly rationalistic: and the negative side of his philosophy was well calculated to lay the foundations of another school of theological rationalists (often called Vulgär-rationalismus), of whom Tieftrunk (died 1837), Bretschneider (1776-1848), and Wegscheider (1771-1849) may be taken as representatives. De Wette (1780-1849) shows the transition to Schleiermacher, who (though in the English sense of the word he was an outspoken rationalist) combined what was best in the opposing schools of rationalists and supernaturalists, founded a higher and truer religious philosophy, and heralded even the 'pectoral theology' of the mediation school.
But it was not in the sphere of speculation and dogma, but in that of biblical criticism, that German rationalism accomplished its main work, and left its deepest mark on subsequent theological development. In the early 18th century the 'Germans in Greek were sadly to seek,' as English scholars thought: the Germans themselves admitted that in studying the Scriptures they failed to escape from dogmatic presuppositions, and that it was the English divines who approached the New Testament in a historical spirit, which in the Germany of that day caused misgivings. It is noteworthy that Semler (1725-91), 'the father of rationalism,' obtained the doctorate for a thesis written against Whiston, Bentley, and other English scholars in defence of the 'three heavenly witnesses' of 1 John, v. 7. Semler in the schools, supported by Lessing and Herder in literature, was soon teaching that the books of the Bible must be studied as human productions: Eichhorn (1752-1827) thoroughly accepted and applied that principle. Rationalist criticism was carried to an absurd length by Paulus (1761-1851), who taught that the Gospels contained natural and not supernatural events, and whose most ingenious but inept 'explanations' of the miracles of the New Testament, 'retaining everywhere the husk but surrendering the religious kernel,' were made a laughing-stock by Strauss. Strauss's 'mythical theory' (excessively rationalist in the English sense of the term) was in its turn superseded by Baur (q.v.) and the new Tübingen school, whose epoch-making work marks the opening of the most recent period in scriptural criticism. The 'notes' of the newer criticism, whether more or less rationalist from the older English point of view, are the conviction that all truth is one, whether derived from the natural sciences, historical research, the dictates of conscience, or the records of divine revelation, and the willingness to accept what is apparently established by the consensus of scholars even where this involves giving up the belief in the inerrancy of Scripture. Many of the contentions of self-confident and aggressive rationalism have long since mutually destroyed one another. Nothing can be more contrary to the true historic and scientific spirit than the assumptions of a reckless sciolism: there is a false and a true rationalism; and it should be remembered that much that is now most surely believed by all has at one time or another been branded as rationalistic.
See the church histories; Tholuck, Vorgeschichte des Rationalismus (1853) and Geschichte des Rationalismus (1865, unfinished), and earlier monographs by Stäudlin and Rückert; H. J. Rose's essay On the State of Religion in Protestant Germany (1825), and Pusey's Historical Inquiry into the Causes of the Rationalist Character of the Theology of Germany (1828-30); A. S. Farrar, Critical History of Free Thought (1862); R. W. Mackay, The Tübingen School and its Antecedents (1863); Lecky, History of Rationalism in Europe (1865); Hurst, History of Rationalism (New York, 1866); Fisher, Faith and Rationalism (New York, 1879); Tulloch's Rational Theology (1872) and Movements of Religious Thought (1885); Draper, Intellectual Development of Europe (1867) and Conflict between Science and Religion (1874); Cairns, Unbelief in the Eighteenth Century (1881); Pfeiderer, The Development of Theology in Germany since Kant (Lond. 1890); also the articles in this work on CHURCH HISTORY, REFORMATION, DEISM, EXEGESIS, and works there cited, with the articles on the chief rationalist critics and thinkers.