A fuller and more detailed definition of the dialectic as applied by Engels is given by that philosopher in his famous reply to Eugene Duhring known as the "Umwaelzung der Wissenschaft." In that work a more thorough and patient investigation is made into the sources of materialistic philosophy of the socialist movement, for the reputation of his antagonist appears to have acted as a spur to Engels' faculties which certainly never showed to better advantage than in that work. A portion of the argument, in fact an abstract of the general train of reasoning, with the omission of the more obviously controversial parts, has been reprinted under the title of "Socialism from Utopia to Science." The following quotation is taken from the translation prepared for the "People" in 1892: "We also find, upon a closer enquiry, that the two poles of an antithesis, such as positive and negative, are as inseparable from as they are opposed to each other, and that, despite their antagonism, they mutually pervade each other; and in the same way we find cause and effect to be conceptions whose force exists only when applied to a single instance, but which, soon as we consider that instance in its connection with the cosmos, run into each other and dissolve in the contemplation of that universal action and reaction where cause and effect constantly change places--that which is effect, now and here, becoming, then and yonder, cause, and vice versa. "None of these processes and methods of reasoning fits in the metaphysical framework of thought. To dialectics, however, which takes in the objects and their conceivable images above all in their connections, their sequence, their motion, their rise and decline, processes like the above are so many attestations of its own method of procedure. Nature furnishes the test to dialectics, and this much we must say for modern natural science, that it has contributed towards this test an extremely rich and daily increasing material, whereby it has demonstrated that, in the last instance, nature proceeds upon dialectical, not upon metaphysical methods, that it does not move upon the eternal sameness of a perpetually recurring circle, but that it goes through an actual historic evolution.