When, later, I published an independent work, I had already grown a good bit more stupid. For now a well meaning critic offered the advice: “Before he goes on reforming further and gives his _Philosophy of Freedom_ to the world, he should be pressingly advised first to work himself through to an understanding of these two philosophers [Hume and Kant].” The critic unfortunately knows only so much as he is himself able to read in Kant and Hume; practically, therefore, he simply advises me to learn to see no more in these thinkers than he himself sees. When I have attained that, he will be satisfied with me. Then when my _Philosophy and Freedom_ appeared, I was found to be as much in need of correction as the most ignorant beginner. This I received from a gentleman who probably nothing else impelled to the writing of books except that he had not understood innumerable foreign ones. He gravely informs me that I should have noticed my mistakes if I had “made more thorough studies in psychology, logic, and the theory of knowledge”; and he enumerates forthwith the books I ought to read to become as wise as himself: “Mill, Sigwart, Wundt, Riehl, Paulsen, B. Erdmann.” What amused me especially was this advice from a man who was so “impressed” with the way he “understood” Kant that he could not even imagine how any man could have read Kant and yet judge otherwise than himself. He therefore indicates to me the exact chapters in question in Kant’s writings from which I may be able to obtain an understanding of Kant as deep and as thorough as his own. I have cited here a couple of typical criticisms of my world of ideas. Though in themselves unimportant, yet they seem to me to point, as symptoms, to facts which present themselves to-day as serious obstacles in the path of any one aiming at literary activity in regard to the higher problems of knowledge. Thus I must go on my way, indifferent, whether one man gives me the good advice to read Kant, or another hunts me as a heretic because I agree with Haeckel. And so I have also written upon Mysticism, wholly indifferent as to how a faithful and believing materialist may judge of me. I would only like--so that printers’ ink may not be wasted wholly without need--to inform any one who may perchance advise me to read Haeckel’s _Riddle of the Universe_, that during the last few months I have delivered about thirty lectures upon the said work. I hope to have shown in this book that one may be a faithful adherent of the scientific conception of the world and yet be able to seek out those paths to the Soul along which Mysticism, rightly understood, leads. I even go further and say: Only he who knows the Spirit, in the sense of true Mysticism, can attain a full understanding of the facts of Nature. But one must not confuse true Mysticism with the “pseudo-mysticism” of ill-ordered minds. How Mysticism can err, I have shown in my _Philosophy of Freedom_ (page 131 _et seq._).