The varieties of what one may term the rationalistic error, of the endeavor of the intellect to emancipate itself from perception and set up as an independent power, are numerous. The variety that was perhaps formerly most familiar was that of the theologian who sought to formulate intellectually what must ever transcend formulation. The forms of the rationalistic error that concern our present subject can be traced back for the most part to Descartes, the father of modern philosophy, and are indeed implicit in his famous identification of thought and being (_Je pense, donc je suis_). The dogmatic and arrogant rationalism that denies both what is above and what is below itself, both the realm of awe and the realm of wonder, which prevailed among the Cartesians of the Enlightenment, combined, as I have said, with pseudo-classic decorum to produce that sense of confinement and smugness against which the original genius protested. Man will always crave a view of life to which perception lends immediacy and the imagination infinitude. A view of life like that of the eighteenth century that reduces unduly the rôle of both imagination and perception will always seem to him unvital and mechanical. “The Bounded,” says Blake, “is loathed by its possessor. The same dull round even of a Universe would soon become a Mill with complicated wheels.” The mechanizing of life against which the romanticist protested may as I said be largely associated with the influence of Descartes. It is not however the whole truth about Descartes to say that he forgot the purely instrumental rôle of the intellect and encouraged it to set up as an independent power. As a matter of fact he also used the intellect as an instrument in the service of outer perception. Taking as his point of departure the precise observations that science was accumulating, he sought to formulate mathematically the natural law. Now the more one reduces nature to a problem of space and movement, the more one is enabled to measure nature; and the method of exact measurement may be justified, if not on metaphysical, at least on practical grounds. It helps one, if not to understand natural forces, at least to control them. It thereby increases man’s power and ministers to utility. In a word, the intellect when thus pressed into the service of outer perception makes for material efficiency. In a sense science becomes scientific only in proportion as it neglects the qualitative differences between phenomena, e.g. between light and sound, and treats them solely from the point of view of quantity. But the penalty that science pays for this quantitative method is a heavy one. The farther it gets away from the warm immediacy of perception the less real it becomes; for that only is real to a man that he immediately perceives. Perfectly pure science tends to become a series of abstract mathematical formulæ without any real content. By his resort to such a method, the man of science is in constant danger of