Where I wished to make changes had particular reference to two points. In the first place with regard to primitive history, as far as known, to which Morgan was the first to give us the key in 1877. In my book "The Origin of the Family, Private Property and the State," Zurich, 1884, I have since had an opportunity of working up material more lately accessible which I employed in this later work. In the second place, as far as that portion which is concerned with theoretical science is concerned, the presentation of the subject is very defective and a much more definite one could now be given. If I did not allow myself the right of improving it now, I should be in duty bound to pass criticism on myself instead of the other.
Marx and I were probably the first to import the well known dialectic of the German idealistic philosophy into the materialistic view of nature and history. But to a dialectical and at the same time materialistic view of nature there pertains an acquaintance with mathematics and natural science. Marx was a sound mathematician but the sciences we only knew in part, by fits and starts, sporadically. After I retired from mercantile pursuits and went to London and had time, I made as far as possible a complete mathematical and scientific "molting," as Liebig calls it, and spent the best part of eight years on it. I was occupied with this molting process when it chanced that I was called upon to busy myself with Herr Duehring's so-called philosophy. If, therefore, I often fail to find the correct technical expression, and am a little awkward in the field of natural science it is only too natural. On the other hand the consciousness of insecurity which I have not yet got over has made me cautious. Actual blunders respecting facts up to the present known, and incorrect presentations of theories thus far recognised cannot be proved against me. In this relation just one great mathematician, who is laboring under a mistake, has complained to Marx in a letter that I have made a mischievous attack upon the honor of the square root of minus one.
As regards my review of mathematics and the natural science it was necessary for me to reassure myself on some special points – since I had no doubts about the truth of the general proposition – that in nature the same dialectic laws of progress fulfill themselves amid all the apparent confusion of innumerable changes as dominate the apparently accidental in nature; the same laws whose threads traverse the progressive history of human thought, and little by little come to the consciousness of thinking men. These were first developed by Hegel in a comprehensive fashion but in a mystical form. Our efforts were directed towards stripping away this mystical form and making them evident in their full simplicity and universal reality. It was self evident that the old philosophies of nature – in spite of all their actual value and fruitful suggestiveness – could be of no value to us. There was an error in the Hegelian form, as shown in this book, in that it recognised no progression of nature in time, no "one after another" (Nacheinander) but merely "one besides another" (Nebeneinander). This was due on the one hand to the Hegelian system itself which ascribed to the Spirit (Geist) alone a progressive historical development, but on the other hand, the general attitude of the natural sciences was responsible. So Hegel fell far behind Kant in this respect for the latter had already by his nebular hypothesis proclaimed the origin and, by his discovery of the stoppage of the rotation of the earth through the tides, the destruction of the solar system. And finally, I could not undertake to construct the dialectical laws of nature but to discover them in it and to develop them from it.
To do this entirely and in each separate division is a colossal task. Not only is the ground to be covered almost immeasurable but on this entire ground natural science is involved in such tremendous changes that even those who have all their time to give can hardly keep up with it. Since the death of Marx however my mind has been occupied by more pressing duties and so I had to interrupt my work. I must, for the moment, confine myself to the hints in the work before us and wait for a later opportunity to correct and publish the results obtained, probably together with the most important manuscripts on mathematics left behind by Marx.
But the advance of theoretical science makes my work in all probability, in a great measure, or altogether, superfluous. Since the revolution which overturned theoretical science the necessity of arranging the accumulation of purely empirical discoveries has caused the opposing empiricists to pay more and more attention to the dialectical character of the operations of nature. The old stiff antagonisms, the sharp impassable frontier lines are becoming more and more abolished. Since the last "true" gases have been liquefied, since the proof that a body can be put in a condition in which liquid and gaseous forms cannot be differentiated, aggregate conditions have to the last remnant lost their earlier absolute character. With the statement of the kinetic theory of gases that, in gases, the squares of the speeds with which the separate gas molecules move are in inverse ratio to the molecular weights, under the same temperature, heat takes its place directly in the series of such measurable forms of motion. Ten years ago the newly discovered great fundamental law of motion was still understood as a mere law of the conservation of energy, as a mere expression of the indestructibility and uncreatibility of motion, and therefore merely on its quantitative side. That narrow negative expression has been more and more subordinated to the transformation of energy, in which the qualitative content of the process is duly recognised and the last notion of an extramundane Creator is destroyed. That the quantity of motion (of energy, so called) is not changed when it is transformed into kinetic energy (mechanical force, so called), into electricity, heat, potential static energy need not now be preached any longer as something new, it served as the foundation, once attained, of many valuable investigations of the process of transformation itself, of the great fundamental process, in the knowledge of which is comprehended the knowledge of all nature. And since biology has been treated in the light of the theory of evolution it has abolished one stiff line of classification after another in the realm of organic nature. The entirely unclassified intermediate conditions increase in number every day. Later investigations throw organisms out of one class into another, and marks of distinction which have become articles of faith lose their individual reality. We have now mammals which lay eggs and, if the news is established, birds also which go on all fours. It was already observed, before the time of Virchow, as a conclusion of the discovery of the cell, that the identity of the individual creature is lost, scientifically and dialectically speaking, in a federation of cells, so the idea of animal (and therefore human) individuality is still further complicated by the discovery of the amœba in the bodies of the higher animals constituting the white blood corpuscles. And these are just the things which were considered polar opposites, irreconcilable and insoluble, the fixed boundaries and differences of classification, which have given modern theoretical science its limited and metaphysical character. The knowledge that these distinctions and antagonisms actually do occur in nature, but only relatively, and that on the other hand that fixity and absoluteness are the products of our own minds – this knowledge constitutes the kernel of the dialectic view of nature. The view is reached under the compulsion of the mass of scientific facts, and one reaches it the more easily by bringing to the dialectic character of these facts a consciousness of the laws of dialectic thought. At all events, the scope of science is now so great that it no longer escapes the dialectic comprehension. But it will simplify the process if it is remembered that the results in which these discoveries are comprehended are ideas, that the art of operating with ideas is not inborn, moreover, and is not vouchsafed every day to the ordinary mind, but requires actual thought, and this thought has a long history crammed with experiences, neither more nor less than the accumulated experiences of investigation into nature. By these means, then, it learns how to appropriate the results of fifteen hundred years development of philosophy, it gets rid of any separate natural philosophy which stands above or alongside of it and the limited method of thought brought over from