Descartes, in the winter of 1619-20 entered his stove and spent the day in meditation.
"When he went in, his philosophy was half-baked. When he emerged, it was complete in basic essentials. As a first principle he resolved 'never to accept anything for true which I did not clearly know to be such.' His ideal and method were modeled on mathematics. 'The long chains', he went on, 'of simple and easy reasonings by means of which geometers are accustomed to reach the conclusions of their most difficult demonstrations, had led me to imagine that all things, to the knowledge of which man is competent, are mutually connected in the same way, and that there is nothing so far removed from us as to be beyond our reach....'"
--- Colin Brown, Philosophy and the Christian Faith, Inter-Varsity Press (1968), p. 50.
John Locke (1632-1704), a founder of British empiricism, was one of the first to articulate this view:
"Reason is natural revelation, whereby the eternal Father of light, and fountainhead of all knowledge, communicates to mankind that portion of truth which he has laid within the reach of their natural faculties; Revelation is natural reason enlarged by a new set of discoveries communicated by God immediately, which reason vouches the truth of, by the testimony and proof it gives that they come from God."
-- John Locke, An Essay Concerning Human Understanding (1690).
Following is a modern critique of empiricism and rationalism, which Wolterstorff calls 'foundationalism':
"The classic theory of theorizing in the Western world is foundationalism. Simply put, the goal of scientific endeavor, according to the foundationalist, is to form a body of theories from which all prejudice, bias and unjustified conjecture have been eliminated. To attain this, we must begin with a firm foundation of certitude and build the house of theory on it by methods of whose reliability we are equally certain.... "Essential to the foundationalist's vision is the existence of a body of foundational propositions -- that is, propositions which are not only true but can be known noninferentially and with certitude to be true. Do we have any good reason to think that there are any such propositions?
On all fronts foundationalism is in bad shape. It seems to me that there is nothing to do but give it up for mortally ill and learn to live in its absence. Theorizing is without a foundation of indubitables. .... Our future theories of theorizing will have to be nonfoundationalist ones.
-- N. Wolterstorff, Reason within the Bounds of Religion, Eerdmans (1976).
"Today rationalism is discredited, whether we look at it from the viewpoint of philosophy or that of Christian theology. And, in the last analysis, for the same reason. For it is impossible to construct maps of reality, starting with mere concepts and a priori definitions, without looking to see whether the theories match experience. In the sphere of philosophy this means that the rationalists were on the wrong track in their endeavors to provide a metaphysical understanding of the natural order. But they were also on the wrong track theologically. The god of the rationalists was a hypothetical abstraction, a deus ex machina, invoked to make the system work, but not one who was encountered personally in history and present experience. His existence was, moreover, based upon arguments which we have already seen to be dubious. It is not surprising, therefore, that, when later thinkers rejected the rationalist approach and undermined the old proofs of the existence of God, they felt that God and religion had been disposed of altogether, and that there was no alternative to agnosticism or downright atheism."
--- Colin Brown, Ibid., p. 57.