(Latin: ratio, reason)
(1) A particular moment in the development oj Protestant theology in Germany.
(2) Usually, the doctrine that human reason is the sole source and the final test of all truth.
In this sense rationalism denies the supernatural character of Revelation, and affirms that all religious truths are derived from human reason alone; that human reason is the sole medium by which man can arrive at any truth; that the faith of Christ is unalterably opposed to reason; that Divine Revelation is a hindrance rather than a help to man's perfection; and that the miracles and prophecies narrated in Sacred Scripture are poetic fancies.
In the words of the Vatican Council I, absolute rationalism teaches that "human reason is so independent that faith cannot be commanded it by God."
Reason is a law to itself.
The philosophic principle upon which rationalism is based is that of the absolute autonomy or independence of reason.
Rationalists claim to find the formula for this autonomy in the words of Descartes: "nothing is to be declared true, but what is evidently so"; but Descartes himself admitted that supernatural mysteries were evidently credible on the authority of God revealing them.
According to rationalism, reason is the supreme judge of what is true, what false, what merely symbolic in Sacred Scripture.
Historically, modern rationalism proceeds from the Lutheran principle of private interpretation of the Bible.
The reformers rejected the authority of the Church; the rationalists afterwards rejected the authority of God.
As early as the 16th century some Protestants applying the principle of private interpretation rejected or interpreted symbolically the supernatural mysteries of the Trinity, the Incarnation, the Redemption, and the Eucharist.
The doubts and contradictions arising from private interpretation of Sacred Scripture led many to believe that nothing certain could be known from revelation and hence natural religion sufficed, e.g., Hobbes, Hume, Voltaire, Rousseau, Spinoza, and Wolff.
New Catholic Dictionary