When three years ago, Herr Duehring suddenly challenged the world, as a scholar and reformer of socialism, friends in Germany frequently expressed the wish that I should throw a critical light upon these new socialist doctrines, in the central organ of the Social Democratic Party, at that time the "Volkstaat." They held it as very necessary that new opportunity for division and confusion should not be afforded in a party so young and so recently definitely united. They were in a better condition than myself to comprehend the condition of affairs in Germany, so that I was compelled to trust to their judgment. It appeared furthermore that the proselyte was welcomed by a certain portion of the socialist press, with a warmth, which meant nothing more than kindliness to Herr Duehring, but it was seen by a portion of the party press that a result of this kindly feeling towards Herr Duehring was the introduction unperceived of the Duehring doctrine. People were found who were soon ready to spread his doctrine in a popular form among the workingmen, and finally Herr Duehring and his little sect employed all the arts of advertisement and intrigue to compel the "Volksblatt" to change its attitude respecting the new teachings which put forth such tremendous claims. However, a year elapsed before I could make up my mind to engage in so disagreeable a business to the neglect of my other labors. It was the sort of thing one had to get through as quickly as possible, once it was begun. And it was not only unpleasant but quite a task. The new socialist theory appeared as the last practical result of a new philosophic system. It therefore involved an investigation of it in connection with this system and therefore of the system itself. It was necessary to follow Herr Duehring over a wide expanse of country where he had dealt with everything under the sun, yea, and more also. So there came into existence a series of articles which appeared from the beginning of 1877 in the successor of the "Volkstaat," the "Vorwaerts" of Leipsic, and are collected here. It was my object which extended the criticism to a length out of all proportion to the scientific value of the matter and, therefore, of Herr Duehring's writings. There are two further reasons in extenuation of this lengthiness. In the first place it gave me an opportunity of developing my views, in a positive fashion, with respect to matters which are connected with this, though very different, and which are of more general scientific and practical interest to-day. I have taken the opportunity to do so in every chapter, and, as this book cannot undertake to set up a system in opposition to that of Herr Duehring, it is to be hoped that the reader will not overlook the real significance of the views which I have set forth. I have already had sufficient proof that my labors have not been altogether in vain in this regard.