§ 174. Absolute idealism, which is essentially a modern doctrine, does not begin with rhapsodies, but with a very sober analysis of familiar truths, conducted by the most sober of all philosophers, Immanuel Kant. This philosopher lived in Königsberg, Germany, at the close of the eighteenth century. He is related to absolute idealism much as Socrates is related to Platonism: he was not himself speculative, but employed a critical method which was transformed by his followers into a metaphysical construction. It is essential to the understanding both of Kant and of his more speculative successors, to observe that he begins with the recognition of certain non-philosophical truths--those of _natural science_ and _the moral consciousness_. He accepts the order of nature formulated in the Newtonian dynamics, and the moral order acknowledged in the common human conviction of duty. And he is interested in discovering the ground upon which these common affirmations rest, the structure which virtually supports them as types of knowledge. But a general importance attaches to the analysis because these two types of knowledge (together with the æsthetic judgment, which is similarly analyzed) are regarded by Kant as coextensive with experience itself. The _very least experience_ that can be reported upon at all is an experience of nature or duty, and as such will be informed with their characteristic principles. Let us consider the former type. The simplest instance of nature is the experience of the single perceived object. In the first place, such an object will be perceived as in space and time. These Kant calls the _forms of intuition_. An object cannot even be presented or given without them. But, furthermore, it will be regarded as substance, that is, as having a substratum that persists through changes of position or quality. It will also be regarded as causally dependent upon other objects like itself. Causality, substance, and like principles to the number of twelve, Kant calls the _categories of the understanding_. Both intuition and understanding are indispensable to the experience of any object whatsoever. They may be said to condition the object in general. Their principles condition the process of making something out of the manifold of sensation. But similarly, every moral experience recognizes what Kant calls _the categorical imperative_. The categorical imperative is the law of reasonableness or impartiality in conduct, requiring the individual to act on a maxim which he can "will to be law universal." No state of desire or situation calling for action means anything morally except in the light of this obligation. Thus certain principles of thought and action are said to be implicit in all experience. They are universal and necessary in the sense that they are discovered as the conditions not of any particular experience, but of experience in general. This implicit or virtual presence in experience in general,