(a) In the introduction to the "Critique of Political Economy" Marx summarised his views as follows:
"In the social production which men carry on they enter into definite relations that are indispensable and independent of their will; these relations of production correspond to a definite stage of development of their material powers of production. The sum total of these relations of production constitutes the economic structure of society - the real foundation, on which rise legal and political superstructures and to which correspond definite forms of social consciousness. The mode of production in material life determines the general character of the social, political and spiritual processes of life. It is not the consciousness of men that determines their existence, but, on the contrary, their social existence determines their consciousness. At a certain stage of their development, the material forces of production in society come in conflict with the existing relations of production, or - what is but a legal expression of the same thing - with the property relations within which they had been at work before. From forms of development of the forces of production these relations turn into their fetters. Then comes the period of social revolution. With the change of the economic foundation the entire immense superstructure is more or less rapidly transformed. In considering such transformations the distinction should always be made between the material transformation of the economic conditions of production which can be determined with the precision of natural science, and the legal, political, religious, aesthetic or philosophic - in short ideological forms in which men become conscious of this conflict and fight it out. Just as our opinion of an individual is not based on what he thinks of himself, so can we not judge of such a period of transformation by its own consciousness; on the contrary, this consciousness must rather be explained from the contradictions of material life, from the existing conflict between the social forces of production and the relations of production. No social order ever disappears before all the productive forces, for which there is room in it, have been developed; and new higher relations of production never appear before the material conditions of their existence have matured in the womb of the old society. Therefore, mankind always takes up only such problems as it can solve; since, looking at the matter more closely, we will always find that the problem itself arises only when the material conditions necessary for its solution already exist or are at least in the process of formation. In broad outlines we can designate the asiatic, the ancient, the feudal, and the modem bourgeois methods of production as so many epochs in the progress of the economic formation of society. The bourgeois relations of production are the last antagonistic form of the social process of production - antagonistic not in the sense of individual antagonism, but of one arising from conditions surrounding the life of individuals in society; at the same time the productive forces developing in the womb of bourgeois society create the material conditions for the solution of that antagonism. This social formation constitutes, therefore the closing chapter of the prehistoric stage of human society."

In his preface to Volume I of "Capital" Marx added the following to the above statement:
"One nation can and should learn from others. And even when a society has got upon the right track for the discovery of the natural laws of its movement - and it is the ultimate aim of this work to lay bare the economic law of motion of modern society - it can neither clear by bold leaps, nor remove by legal enactments, the obstacles offered by the successive phases of its normal development. But it can shorten and lessen the birth pangs."

In the second paragraph of the "Eighteenth Brumaire of Louis Bonaparte" he made another addition:
"Man makes his own history, but does not make it out of conditions chosen by himself, but out of such as he finds close at hand. The tradition of all past generations weighs like an alp upon the brain of the living."

Just one or two notes relating to the above:

It will be noticed that the method of production determines the general character, not the character of each individual. That the relations turn into fetters - like feudal land holding, the closed guilds, and the objections to investment for profit which fettered the development of capitalism. Distinction must be made between the transformation of the conditions of production and the ideological forms under which the fight was carried on. The religious wars towards the end of the Middle Ages were the ideological reflection of the growth of capitalism. One nation can learn from others. This is happening in Africa and is the source of much turmoil. Also the Aborigines of Australia have jumped right into capitalism owing to the European colonisation. Margaret Mead, in "New Lives for Old", relates that she witnessed amongst the Manus of Polynesia a people who had travelled from the stone age to modern culture in the space of twenty-five years. This happened because of the presence of an American Army on the island during the last war.

In his Poverty of Philosophy, Marx made reference to the development of all the productive forces:
"In order for the oppressed class to be emancipated it is necessary that the productive powers already acquired and the existing social relations should no longer 'be able to exist side by side. Of all the instruments of production the greatest productive power is the revolutionary class itself. The organisation of the revolutionary elements as a class supposes the existence of all the productive forces which can be engendered in the bosom of the old society."

The above statements by Marx should make his attitude on the subject quite clear, though it has not prevented exaggerations and misinterpretations.

(b) In reply to a letter from a young student Engels made the following statement:
"According to the materialist conception of history, the factor which is in the last instance decisive in history is the production and reproduction of actual life. More than this neither Marx nor myself ever claimed. If now someone has distorted the meaning in such a way that the economic factor is the only decisive one, this man has changed the above pro-position into an abstract, absurd phrase which says nothing. The economic situation is the base, but the different parts of the structure - the political forms of the class struggle and its results, the constitutions established by the victorious class after the battle is won, forms of law and even the reflections of all these real struggles in the brains of the participants, political theories, juridical, philosophical, religious opinions, and their further development into dogmatic systems @ all this exercises also its influence on the development of the historical struggles and in cases determines their form.".

(c) In The Poverty of Philosophy (p.190, Kerr ed.), Marx indicated the changed form of social development when class divided society gives place to "an association which will exclude classes and their antagonisms":

"It is only in an order of things in which there will be no longer classes or class antagonism that social evolutions will cease to be political revolutions."