The words which I have italicised form a very necessary correction of the first edition preface, according to which the _Critique_ would seem to “treat only of reason and its pure thinking.” A further difference follows. The second edition preface, in thus emphasising the objective aspect of the problem, is led to characterise in a more complete manner the method to be followed in the Critical enquiry. How can the _Critique_, if it is concerned, as both editions agree in insisting, only with the _a priori_ which originates in human reason, solve the specifically metaphysical problem, viz. that of determining the independently real? How can an idea in us refer to, and constitute knowledge of, an object? The larger part of the preface to the second edition is devoted to the Critical solution of this problem. The argument of the _Dialectic_ is no longer emphasised at the expense of the _Analytic_. Kant points out that as a matter of historical fact each of the two rational sciences, mathematics and physics, first entered upon the assured path of knowledge by a sudden revolution, and by the adoption of a method which in its general characteristics is common to both. This method consists, not in being led by nature as in leading-strings, but in interrogating nature in accordance with what reason produces on its own plan. The method of the geometrician does not consist in the study of figures presented to the senses. That would be an empirical (in Kant’s view, sceptical) method. Geometrical propositions could not then be regarded as possessing universality and necessity. Nor does the geometrician employ a dogmatic method, that of studying the mere conception of a figure. By that means no new knowledge could ever be attained. The actual method consists in interpreting the sensible figures through conceptions that have been rigorously defined, and in accordance with which the figures have been constructively generated. The first discovery of this method, by Thales or some other Greek, was “far more important than the discovery of the passage round the celebrated Cape of Good Hope.”[112] Some two thousand years elapsed before Galileo formulated a corresponding method for physical science. He relied neither on mere observation nor on his own conceptions. He determined the principles according to which alone concordant phenomena can be admitted as laws of nature, and then by experiment compelled nature to answer the questions which these principles suggest. Here again the method is neither merely empirical nor purely dogmatic. It possesses the advantages of both.