The second historic event centers about the controversy of innate ideas, or pure concepts. The issue is between empiricism and rationalism as theories of the origin and validation of scientific knowledge. The empiricist is he who feels that the chief obstacle which prevents scientific method from making way is the belief in pure thoughts, not derived from particular observations and hence not responsible to the course of experience. His objection to the “high _a priori_ road” is that it introduces in irresponsible fashion a mode of presumed knowledge which may be used at any turn to stand sponsor for mere tradition and prejudice, and thus to nullify the results of science resting upon and verified by observable facts. Experience thus comes to mean, to use the words of Peirce, “that which is forced upon a man’s recognition will-he, nill-he, and shapes his thoughts to something quite different from what they naturally would have taken.”[31] The same definition is found in James, in his chapter on Necessary Truths: “Experience means experience of something foreign supposed to impress us whether spontaneously or in consequence of our own exertions and acts.”[32] As Peirce points out, this notion of experience as the foreign element that forces the hand of thought and controls its efficacy, goes back to Locke. Experience is “observation employed either about external sensible objects, or about the internal operations of our minds”[33]--as furnishing in short all the valid data and tests of thinking and knowledge. This meaning, thinks Peirce, should be accepted “as a landmark which it would be a crime to disturb or displace.” The contention of idealism, here bound up with rationalism, is that perception and observation cannot guarantee knowledge in its honorific sense (science); that the peculiar differentia of scientific knowledge is a constancy, a universality, and necessity that contrast at every point with perceptual data, and that indispensably require the function of conception.[34] In short, _qualitative transformation_ of _facts_ (data of perception), not their mechanical subtraction and recombination, is the difference between scientific and perceptual knowledge. Here the problem which emerges is, of course, the significance of perception and of conception in respect to experience.[35]