Faced with the misinterpretations and incomprehensions of numerous epigones, Friedrich Engels had to clarify in various correspondences what the method of historical materialism that K. Marx and himself had developed was. Still today, and more than ever, it is highly useful to read or re-read them to attempt to make this method our own, so that we can grasp and understand the various shake-ups that the capitalist world has gone through since 2008. Evidently, it is not a question of making it into a dogma, which, in fact, would already be giving it up and betraying it. There is no recipe or list of criteria to understand it, to apply and develop it for each particular situation. On the contrary, it is important to utilize “this materialist dialectic” that Engels defined as “our best working tool and our sharpest weapon” (L. Feuerbach and the End of Classical Philosophy) to try to understand the fundamental meaning of the events and the dynamic which underlies them; to grasp the motive force that provokes what are presented to us as “irrational accidents”, like the Brexit victory, Trump’s election, or still the threats of nuclear war with North Korea…; so that we don’t allow ourselves to “ be imposed upon by the antithesis, insuperable for the still common old metaphysics, between true and false, good and bad, identical and different, necessary and accidental” (idem) and rational and irrational, we are tempted to add...

F. Engels, Letter to Borgius, (January 25th 1894)

Here is the answer to your questions!

1) What we understand by the economic conditions, which we regard as the determining basis of the history of society, are the methods by which human beings in a given society produce their means of subsistence and exchange the products among themselves (in so far as division of labour exists). Thus the entire technique of production and transport is here included. According to our conception this technique also determines the method of exchange and, further, the division of products, and with it, after the dissolution of tribal society, the division into classes also and hence the relations of lordship and servitude and with them the state, politics, law, etc. Under economic conditions are further included the geographical basis on which they operate and those remnants of earlier stages of economic development which have actually been transmitted and have survived – often only through tradition or the force of inertia; also of course the external milieu which surrounds this form of society.

If, as you say, technique largely depends on the state of science, science depends far more still on the state and the requirements of technique. If society has a technical need, that helps science forward more than ten universities. The whole of hydrostatics (Torricelli, etc.) was called forth by the necessity for regulating the mountain streams of Italy in the sixteenth and seventeenth centuries. We have only known anything reasonable about electricity since its technical applicability was discovered. But unfortunately it has become the custom in Germany to write the history of the sciences as if they had fallen from the skies.

2) We regard economic conditions as the factor which ultimately determines historical development. But race is itself an economic factor. Here, however, two points must not be overlooked:

a) Political, juridical, philosophical, religious, literary, artistic, etc., development is based on economic development. But all these react upon one another and also upon the economic base. It is not that the economic position is the cause and alone active, while everything else only has a passive effect. There is, rather, interaction on the basis of the economic necessity, which ultimately always asserts itself. The state, for instance, exercises an influence by tariffs, free trade, good or bad fiscal system; and even the deadly inanition and impotence of the German petty bourgeois, arising from the miserable economic position of Germany from 1640 to 1830 and expressing itself at first in pietism, then in sentimentality and cringing servility to princes and nobles, was not without economic effect. It was one of the greatest hindrances to recovery and was not shaken until the revolutionary and Napoleonic wars made the chronic misery an acute one. So it is not, as people try here and there conveniently to imagine, that the economic position produces an automatic effect. Men make their history themselves, only in given surroundings which condition it and on the basis of actual relations already existing, among which the economic relations, however much they may be influenced by the other political and ideological ones, are still ultimately the decisive ones, forming the red thread which runs through them and alone leads to understanding.

b) Men make their history themselves, but not as yet with a collective will or according to a collective plan or even in a definitely defined, given society. Their efforts clash, and for that very reason all such societies are governed by necessity, which is supplemented by and appears under the forms of accident. The necessity which here asserts itself amidst all accident is again ultimately economic necessity. This is where the so-called great men come in for treatment. That such and such a man and precisely that man arises at that particular time in that given country is of course pure accident. But cut him out and there will be a demand for a substitute, and this substitute will be found, good or bad, but in the long run he will be found. That Napoleon, just that particular Corsican, should have been the military dictator whom the French Republic, exhausted by its own war, had rendered necessary, was an accident; but that, if a Napoleon had been lacking, another would have filled the place, is proved by the fact that the man has always been found as soon as he became necessary: Caesar, Augustus, Cromwell, etc. While Marx discovered the materialist conception of history, Thierry, Mignet, Guizot, and all the English historians up to 1850 are the proof that it was being striven for, and the discovery of the same conception by Morgan proves that the time was ripe for it and that indeed it had to be discovered.

So with all the other accidents, and apparent accidents, of history. The further the particular sphere which we are investigating is removed from the economic sphere and approaches that of pure abstract ideology, the more shall we find it exhibiting accidents in its development, the more will its curve run in a zig-zag. So also you will find that the axis of this curve will approach more and more nearly parallel to the axis of the curve of economic development the longer the period considered and the wider the field dealt with.

In Germany the greatest hindrance to correct understanding is the irresponsible neglect by literature of economic history. It is so hard, not only to disaccustom oneself of the ideas of history drilled into one at school, but still more to rake up the necessary material for doing so. Who, for instance, has read old G. von Gülich, whose dry collection of material nevertheless contains so much stuff for the clarification of innumerable political facts!

For the rest, the fine example which Marx has given in the Eighteenth Brumaire should already, I think, provide you fairly well with information on your questions, just because it is a practical example. I have also, I believe, already touched on most of the points in Anti-Dühring I, Chapters 9-11, and II, 2-4, as well as in III, I, or Introduction, and then in the last section of Feuerbach.

Please do not weigh each word in the above too carefully, but keep the connection in mind; I regret that I have not the time to work out what I am writing to you so exactly as I should be obliged to do for publication.