This is the majority of Marx’s preface to A Contribution to the Critique of Political Economy. This work would essentially be superseded by the presentation of the same ideas in a more complete and developed form in Capital, I (1867). However, this preface remains an important stand-alone document because here Marx provides a brief and insightful intellectual autobiography. I chose to present this excerpt with this alternative title (taken from the text) so as to place due focus on this aspect.
— R. D.
Although I studied jurisprudence, I pursued it as a subject subordinated to philosophy and history. In the year 1842-43, as editor of the Rheinische Zeitung, I first found myself in the embarrassing position of having to discuss what is known as material interests. The deliberations of the Rhenish Landtag on forest thefts and the division of landed property; the official polemic started by Herr von Schaper, then Oberprasident of the Rhine Province, against the Rheinische Zeitung about the condition of the Moselle peasantry, and finally the debates on free trade and protective tariffs caused me in the first instance to turn my attention to economic questions. On the other hand, at that time when good intentions “to push forward” often took the place of factual knowledge, an echo of French socialism and communism, slightly tinged by philosophy, was noticeable in the Rheinische Zeitung. I objected to this dilettantism, but at the same time frankly admitted in a controversy with the Allgemeinen Augsburger Zeitung that my previous studies did not allow me to express any opinion on the content of the French theories. When the publishers of the Rheinische Zeitung conceived the illusion that by a more compliant policy on the part of the paper it might be possible to secure the abrogation of the death sentence passed upon it, I eagerly grasped the opportunity to withdraw from the public stage to my study.
The first work which I undertook to dispel the doubts assailing me was a critical re-examination of the Hegelian philosophy of law; the introduction to this work being published in the Deutsch-Französischen Jahrbüchern issued in Paris in 1844. My inquiry led me to the conclusion that neither legal relations nor political forms could be comprehended whether by themselves or on the basis of a so-called general development of the human mind, but that on the contrary they originate in the material conditions of life, the totality of which Hegel, following the example of English and French thinkers of the eighteenth century, embraces within the term “civil society”; that the anatomy of this civil society, however, has to be sought in political economy. The study of this, which I began in Paris, I continued in Brussels, where I moved owing to an expulsion order issued by M. Guizot.
The general conclusion at which I arrived and which, once reached, became the guiding principle of my studies can be summarised as follows: In the social production of their existence, men inevitably enter into definite relations, which are independent of their will, namely relations of production appropriate to a given stage in the development of their material forces of production. The totality of these relations of production constitutes the economic structure of society, the real foundation, on which arises a legal and political superstructure and to which correspond definite forms of social consciousness. The mode of production of material life conditions the general process of social, political and intellectual life. It is not the consciousness of men that determines their existence, but their social existence that determines their consciousness. At a certain stage of development, the material productive forces of society come into conflict with the existing relations of production or — this merely expresses the same thing in legal terms — with the property relations within the framework of which they have operated hitherto. From forms of development of the productive forces these relations turn into their fetters. Then begins an era of social revolution. The changes in the economic foundation lead sooner or later to the transformation of the whole immense superstructure.
In studying such transformations it is always necessary to distinguish 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, artistic or philosophic — in short, ideological forms in which men become conscious of this conflict and fight it out. Just as one does not judge an individual by what he thinks about himself, so one cannot judge such a period of transformation by its consciousness, but, on the contrary, this consciousness must be explained from the contradictions of material life, from the conflict existing between the social forces of production and the relations of production. No social order is ever destroyed before all the productive forces for which it is sufficient have been developed, and new superior relations of production never replace older ones before the material conditions for their existence have matured within the framework of the old society. Mankind thus inevitably sets itself only such tasks as it is able to solve, since closer examination will always show that the problem itself arises only when the material conditions for its solution are already present or at least in the course of formation.
In broad outline, the Asiatic, ancient,  feudal and modern bourgeois modes of production may be designated as epochs marking progress in the economic development of society. The bourgeois mode of production is the last antagonistic form of the social process of production — antagonistic not in the sense of individual antagonism but of an antagonism that emanates from the individuals’ social conditions of existence — but the productive forces developing within bourgeois society create also the material conditions for a solution of this antagonism. The prehistory of human society accordingly closes with this social formation.
Friedrich Engels, with whom I maintained a constant exchange of ideas by correspondence since the publication of his brilliant essay on the critique of economic categories (printed in the Deutsch-Französische Jahrbücher) arrived by another road (compare his The Condition of the Working Class in England. ) at the same result as I, and when in the spring of 1845 he too came to live in Brussels, we decided to set forth together our conception as opposed to the ideological one of German philosophy, in fact to settle accounts with our former philosophical conscience. The intention was carried out in the form of a critique of post-Hegelian philosophy. The manuscript,  two large octavo volumes, had long ago reached the publishers in Westphalia when we were informed that owing to changed circumstances it could not be printed. We abandoned the manuscript to the gnawing criticism of the mice all the more willingly since we had achieved our main purpose — self-clarification.
Of the scattered works in which at that time we presented one or another aspect of our views to the public, I shall mention only the Manifesto of the Communist Party,  jointly written by Engels and myself, and a Discourse on Free Trade,  which I myself published. The salient points of our conception were first outlined in an academic, although polemical, form in my The Poverty of Philosophy.  This book, which was aimed at Proudhon, appeared in 1847. The publication of an essay on wage-labour written in German,  in which I combined the lectures I had held on this subject at the German Workers’ Association in Brussels, was interrupted by the February Revolution and my forcible removal from Belgium in consequence.
The publication of the Neue Rheinische Zeitung in 1848 and 1849 and subsequent events cut short my economic studies, which I could only resume in London in 1850. The enormous amount of material relating to the history of political economy assembled in the British Museum, the fact that London is a convenient vantage point for the observation of bourgeois society, and finally the new stage of development which this society seemed to have entered with the discovery of gold in California and Australia, induced me to start again from the very beginning and to work carefully through the new material. These studies led partly of their own accord to apparently quite remote subjects on which I had to spend a certain amount of time. But it was in particular the imperative necessity of earning my living which reduced the time at my disposal. My collaboration, continued now for eight years, with the New York Tribune, the leading Anglo-American newspaper, necessitated an excessive fragmentation of my studies, for I wrote only exceptionally newspaper correspondence in the strict sense. Since a considerable part of my contributions consisted of articles dealing with important economic events in Britain and on the continent, I was compelled to become conversant with practical detail which, strictly speaking, lie outside the sphere of political economy.
This sketch of the course of my studies in the domain of political economy is intended merely to show that my views — no matter how they may be judged and how little they conform to the interested prejudices of the ruling classes — are the outcome of conscientious research carried on over many years. At the entrance to science, as at the entrance to hell, the demand must be made:
Qui si convien lasciare ogni sospetto
Ogni viltà convien che qui sia morta. 
 In the idea of an Asiatic mode of production, Marx and Engels were following Hegel’s schema.  As the science progressed, Marx & Engels changed their understanding and descriptions accordingly. They later dropped the idea of a distinctive Asiatic mode of production, and kept four basic forms: tribal, ancient, feudal, and capitalist. See Engels’ second footnote to the 1888 edition of the Communist Manifesto. [web] — R. Rojas.
 Dante, Divina Commedia, III, 14-15: “Here must all distrust be left; All cowardice must here be dead.”