Thus far Hume had gone in the development of idealism,' Whether his theory is consistent from end to end, need not be here discussed. But it is evident that Hume was not lost in the quagmire of subjective idealism. The objective and the subjective are with him akin: the objective is the subjective, which is universal, permanent, and normal. The causal relation has, in the first instance, only a subjective necessity; but through that subjective necessity or its irresistible belief, it generates an objective world. But it has been and is the fortune of philosophers to be known in the philosophical world by some conspicuous red rag of their system which first caught the eye of the bull-like leaders of the human herd. It was so notably with Hobbes and Spinoza; and most of the thinkers whose names appear in the pages of Kant suffer from this curtailment. Descartes, Locke, Leibniz, Berkeley, Hume, are _there_ not the real philosophers, discoverable in their works, but the creatures of historic reputation and of popular simplification who do duty for them.
Kant's Hume is therefore a somewhat imaginary being: the product, partly of imperfect knowledge of Hume's writings, partly of prepossessions derived from a long previous training in German rationalism. Such a Hume was--or would have been, had he existed--a philosopher who 'took the objects of experience for things in themselves,' who 'treated the conception of cause as a false and deceptive illusion,' who did not indeed venture to assail the certainty of mathematics, but held--as regards all knowledge about the existence of things-- 'empiricism to be the sole source of principles,' founding his conclusion mainly on an examination of the causal nexus[7]. This 'note of warning' sounded against the claims of pure reason--as he calls Hume's _Enquiry_ was what about 1762 broke Kant's dogmatic slumber and forced him to give his researches in speculative philosophy a new direction. His first step was to generalise Hume's problem from an inquiry into the origin of the causal idea into a general study of the synthetic principles in knowledge. His next was to attempt to fix the number of these concepts and synthetic principles. And his third was to 'deduce' them: i. e., to prove the reciprocal implication between experience or knowledge and the concepts or categories of intelligence.