For indeed, all really new and great discoveries come from the philosophers, gradually filtering down through technical treatises and reviews, until they reach the level of prose fiction and of poetry, which, since the _Æsthetic,_ we know to be one and the same thing with different empirical manifestations. In truth, the philosophers alone go deeply enough into the essence of things to reach their roots. Thus some philosophy, generally in an extremely diluted form, becomes part of every one's mental furniture and thus the world makes progress and the general level of culture is raised. Thought is democratic in being open to all, aristocratic in being attained only by the few--and that is the only true aristocracy: to be on the same level as the best. Another discovery of Croce's, set forth in this volume for the first time in all the plenitude of its richness, is the theory of Error. The proof of the practical nature of error, of its necessity, and of the fact that we only err because we will to do so, is a marvel of acute and profound analysis. Readers unaccustomed to the dialectic may not at first be prepared to admit the necessary forms of error, that error is not distinct, but opposed to truth and as such its simple dialectic negation, and that truth is thought of truth, which develops by conquering error, which must always exist in every problem. The full understanding of the Crocean theory of error throws a flood of light on all philosophical problems, and has already formed the basis of at least one brilliant study of contemporary philosophy.