A strange thing has happened to the reputation of Frederick Engels in the 100 years since his death. For the vast majority of that time both Engels’ allies and his enemies agreed that he was Marx’s alter ego. Indeed, the very expression “alter ego” was Marx’s own description of his relationship to Engels. Most commentators and virtually all Marxists thought that a lifetime of common work, the undeniable and almost undisturbed years of close personal and political co-operation, spoke for themselves. 
But by the 1960s that easy certainty was faced with a sustained challenge. The first cracks in the Cold War consensus were beginning to appear. The growth of CND, the rise of the New Left and, later, opposition to the Vietnam War inevitably produced an enormous increase in interest in radical ideas in general and Marxist ideas, or what passed for Marxist ideas, in particular. This process necessarily led to a reaction against the stifling conformity of reformism and the oppressive legacy of Stalinism. Much of what was said and written marked a rebirth of interest in the genuine Marxist tradition and delivered a long-delayed blow to the reformist and Stalinist traditions.
Yet the reaction against Stalinism was also shaped by Stalinism, in two senses. Firstly, some of those reacting to Stalinism got no further than adopting another variant of Stalinism, either Maoism, or Third Worldism or the ‘reform Communism’ that came to dominate the Western European Communist Parties. Secondly, even those who broke completely with Stalinism tended to confuse elements of the genuine Marxist tradition with the economic determinism characteristic of Stalinism.
All this led to altered perceptions of the Marxist inheritance. Perhaps inevitably, critics began to search the writings of the founders of Marxism for the seeds of Stalinism and failures of reformism. Many of these developments particularly affected students and so fuelled the expansion of academic Marxism. They also coincided with the wider availability of Marx’s early ‘humanist’ writings. A new consensus emerged, both in academic circles and among many on the left, about the nature of Engels’ thought.
The critics of Engels
One of the first studies to systematically assert a cleavage between Marx’s ideas and those of Engels was George Lichtheim’s Marxism: an Historical and Critical Study, first published in 1961.  Lichtheim insisted that in Marx’s vision “critical thought was validated by revolutionary action”, but in Engels’ scheme “there now appeared a cast-iron system of ‘laws’ from which the inevitability of socialism could be deduced with almost mathematical certainty ... the ‘goal’ was transferred from the here-and-now of conscious activity to a horizon so distant as to be almost invisible.” 
For Marx, Lichtheim claims, “the only nature relevant to the understanding of history was human nature.” Engels therefore broke with Marx when he argued that “historical evolution is an aspect of general (natural) evolution and basically subject to the same ‘laws’.”  This meant that Engels had appropriated Hegel’s heritage quite differently to Marx. Marx had taken from Hegel the importance of self conscious activity in the making of history. In contrast “what really fascinates” Engels “is Hegel’s determinism: his ability to make it appear that nature (and history) follow a pre-ordained course”.  Such a drastic recasting of Marxism inevitably had political consequences:
... determinism in thought making for dogmatism in action. The cast-iron certainty which Engels imported into Marxist thinking found its counterpart at the political level in an unshakable conviction that the stars in their courses were promoting the victory of socialism. 
Consequently, Engels, Kautsky – the leading thinker of the Second International – “and the orthodox school in general” transformed Marxism “from the vision of a unique breakthrough into a doctrine of a casaully determined process analogous to the scheme of Darwinian evolution”. 
Lichtheim’s book rehearses many of the themes that were to become so familiar in other work published over the following 20 years: that Engels replaced Marx’s notion of conscious activity with an empiricist notion of science, that he mistakenly extended Marxism so that it covered the natural as well as the social world, that this inevitably drew him into deterministic and reductionist formulations and that these in turn led him at the end of his life to endorse a reformist political practice on the part of the German Social Democratic Party. And not for the last time the revolutionary, humanist Marx was counterposed to the reformist, determinist Engels by a writer such as Lichtheim who was an opponent of Marxism in theory and a convinced reformist in practice.
After Lichtheim the deluge. Alfred Schmidt’s otherwise more careful and interesting book, The Concept of Nature in Marx, first published in German in 1962, argued that “where Engels passed beyond Marx’s conception of the relation between nature and social history, he relapsed into a dogmatic metaphysic”.  Schmidt also saw a departure from the concerns of the early Marx: “For Engels, nature and man are not united primarily through historical practice; man appears only as a product of evolution and a passive reflection of the process of nature, not however as a productive force”.  By adopting this approach Engels also abandoned Marx’s view of how consciousness is formed:
The movement of thought in Marx is by no means limited to a mere mirroring of the factual. The uncritical reproduction of existing relationships in consciousness has precisely an ideological character for Marx. 
So Schmidt believed that where Marx saw ideas formed in interaction with the material world Engels saw only a crude reflection of the outside world in the brains of human beings, a vulgar “copy theory” of consciousness. By 1969 Lucio Colletti could question, almost in passing:
how far this distortion of Marx’s thought by Kautsky and Plekhanov ...was already prepared, if only in embryo, in some aspects of Engels’s work; and how in general the search for the most general laws of development in nature and history made these attempts a preconstitution of the contamination with Hegelianism and Darwinism. 
He went on to argue that Engels’ influence on the leaders of the Second International was partly a result of “the place given in Engels’ work to philosophical-cosmological development, ‘the philosophy of nature’, in other words, the ‘extension’ of historical materialism into ‘dialectical materialism’.” 
In books as diverse as John Lewis’s The Marxism of Marx (1972), Shlomo Avineri’s widely read textbook The Social and Political Thought of Karl Marx (1970) and Leszek Kolakowski’s sophisticated and profoundly anti-Marxist Main Currents of Marxism (1978) it became an article of faith that Engels had distorted Marx. 
Even authors Paul Walton and Andrew Gamble, who were sympathetic to Marxism at the time they wrote From Alienation to Surplus Value (1972), could conclude that:
[Engels] seems debarred from understanding the real premises of Marx’s method because he seeks to make Marxism an objective science on the model of the natural sciences... he tries to establish the truth of historical materialism by treating human interaction as analogous to the interaction of chemical particles. 
For Gareth Stedman Jones, influenced by Louis Althusser’s structuralism, it was Engels’ “inability adequately to think through the novelty of historical materialism as a science” which “led him to an understandable attempt to fill in the gaps with philosophy – the Hegelian philosophy of his youth”. This not only led to a “lack of any theory of the political instance of social formations” but to Engels embracing “a dangerous implication of the Hegelian theory of knowledge – that everything in reality is, in principle at least, already known”. Thus Engels “unintentionally converted the infant science of historical materialism into the appearance of a finished system, a corpus of absolute knowledge which encompassed the whole of empirical reality”. 
By the early 1970s the pattern was fully established – Engels was the villain. And it did not seem to matter what political or theoretical position a writer set out from – the neo-Kantianism of Colletti, the humanism of Avineri or Schmidt, the Althusserianism of New Left Review contributors – the destination was always the same: Engels was at the root of whatever was wrong with Marxism. With few exceptions,  the argument against Engels had now become a virtual orthodoxy, perhaps best summarised in Norman Levine’s The Tragic Deception: Marx contra Engels (1975) and Terrell Carver’s Marx and Engels, the Intellectual Relationship (1983). Levine states the anti-Engels orthodoxy in its bare essentials:
Engels’ materialism ... was a cold, unremitting, and remorseless system. Men had little impact on fashioning the course of development of history and nature. Rather than being the subject of history, men were basically the passive objects of unrelenting external forces ... Engels’ materialism was mechanistic. 
Naturally, for Levine, it followed that “Engels continuously affirmed the copy theory of knowledge ... there was absolutely no variance, no difference between our comprehension of the external world and the external world itself.” 
Engels’ grave error lay in “making the laws of nature themselves dialectical ... something which Marx himself never attempted”.  Engels “was a unilinear evolutionist”  for whom “causality ... meant additive sequence”  and from whose thought “the notion of human praxis was absent”. Consequently:
Engels’ thought moved from a mechanistic materialist view of the universe to a deterministic view of human history ... it was Engels, not Marx, who was the originator of economic determinism. 
Carver’s work is more qualified and careful in its argument, but it arrives at similar conclusions.  Engels was led to “incorporating the causal laws of physical science and taking them as a model for a covertly academic study of history, ‘thought’ and, somewhat implausibly, current politics”. 
There are many more writers who have argued that Engels was responsible for transforming Marxism into a crude, deterministic philosophy of nature which led to the reformism of the Second International and even Stalinism. To those already quoted could be added Richard Gunn in Marxism Today, Jeff Coulter in Socialist Register, Frederick Bender’s The Betrayal of Marx, Z.A. Jordan’s The Evolution of Dialectical Materialism and many others.  These authors combine different elements of the argument in different ways, and few agree on all the arguments used against Engels, but they say little new.
There are two ways of examining these claims. One is to look at the record of Marx and Engels’ partnership. The second is to study the works in which, both jointly and separately, they elaborated their ideas.
The unity of Marx and Engels’ thought
The most remarkable aspect of the view that there was a fundamental divergence between Marx’s theory and Engels’ thought is that it ignores the evidence of their lifelong partnership. Some considerable intellectual contortion is necessary to overcome the elementary biographical facts of Marx and Engels’ lives. For Terrell Carver “the intellectual relationship between the two living men, however, was very much the story of what they accomplished independently”. These accomplishments “were by no means theoretically coincident”. After Marx’s death “Engels moved into an all-powerful role” in which he “invented dialectics and reconstructed Marx’s life and works accordingly”.  Nor is Carver alone in this kind of assertion. It is common coin among Engels’ critics to insist that he codified Marxism as a rigid dialectical philosophy either without Marx’s explicit approval or after his death. Norman Levine argues:
The height of Engels’ career corresponded with the termination of Marx’s life. It is, therefore, entirely consistent that five of Engels’ major works were published in the years closely preceding Marx’s death, or after the termination of Marx’s life. Anti-Dühring appeared in 1878, Socialism: Scientific and Utopian [sic] in 1882, The Origin of the Family, Private Property and the State in 1884, and Ludwig Feuerbach and the End of Classical German Philosophy in 1888. The Dialectics of Nature was first published in 1927 by Riazanov, although the manuscript itself appears to have been completed by 1882. 
Levine makes a more extraordinary claim when he attempts to answer the obvious question of “why basic intellectual differences between the two men did not come to the surface as tangible and real, articulated and acknowledged dispute”. This is a question to which no convincing reply is easily available. Levine’s answer takes us into the ghost world of “the psychological meaning the friendship had for each”. In this realm “Engels chose to tie himself” to Marx because Marx “would also build a place of fame and renown in time for him”; and Marx needed Engels because “Marx did not find the professional and emotional support he needed from his wife”.  But if we leave the territory of Mills and Boon and return to the world of Marx and Engels a very different picture reveals itself.
The first and most striking point about Marx and Engels’ relationship is the strength of the foundations on which it rested. In the 1840s both men arrived at what would later be known as the historical materialist view of the world. But it is by no means the case that Engels simply followed where Marx led. On the vitally important strategic question of the attitude which the pair took to the trade unions it was Engels who blazed the trail. And the entire content of Marx and Engels’ joint work, The Communist Manifesto, was first outlined by Engels alone in Principles of Communism.
On economic questions Engels led the way, even though Marx’s later work in Capital was the decisive contribution. Marx was still extracting himself from the coils of Hegelian philosophy when Engels wrote his Outlines of a Critique of Political Economy. Not only was this the spur to Marx’s own 40 year immersion in economic analysis, it was also the immediate inspiration for Marx’s own transition to a fully materialist class analysis, a process recorded in his Economic and Philosophical Manuscripts of 1844. Indeed, Marx thought Engels’ work “brilliant” and Capital itself carries the subtitle A Critique of Political Economy. Even Carver admits that “Marx’s manuscript notes on Engels’ essay prefigured the course of his lifework” and that “Marx’s Capital was in effect a much elaborated specification of the contradiction discussed by Engels in his Outlines”. 
Having arrived at a common outlook, Marx and Engels jointly authored two key works which elaborated their views, The Holy Family and The German Ideology. They struggled together to win the organisation they were both involved in, the League of the Just, to their ideas, transforming it into the Communist League. The Communist Manifesto was issued in its name. They went on to fight together in the 1848 revolutions – in Engels’ case literally revolver in hand, on the barricades. This then was the foundation of Marx and Engels’ partnership, forged by intense, common intellectual and practical, political work.
The start of Marx’s exile in England and Engels’ life in Manchester unavoidably altered the pattern of their joint work, but it did not end it. Partly, Marx and Engels chose to specialise in different areas. Partly also this differentiation was forced on them by the economic circumstance of Marx’s poverty and Engels’ decision to support his friend while Marx worked on what became Capital. But these new circumstances did not break the intellectual and political trust between them. When Marx had to write articles for newspapers in order to earn some money he never hesitated to put his name to articles which were, in fact, written by Engels.
In the long gestation of Capital Engels was Marx’s constant adviser, either in their almost daily exchange of letters or in conversation when they paid each other visits. Marx consulted Engels on everything from the correct German translation for “gigs” to rent theory, constant and variable capital, surplus value and exploitation. In August 1862 Marx implored Engels to visit him:
I have overthrown so many old views in my critique [i.e. Capital] that I would at least like to consult you over a few points. Writing about the rubbish is tedious for you and me. 
Constant collaboration continued at every stage of the writing of Capital up to and including the reading of the proofs, which Marx largely entrusted to Engels. Even the presentation of Capital bears Engels’ mark. Looking at the proofs, Engels advised Marx that the dialectical points might be made more historically and that Marx had made “a great mistake” in not following the pattern of Hegel’s Encyclopedia with its short sections and many sub-headings.  Marx followed this advice, but ignored other suggestions, “to proceed dialectically in this regard also”, as he joked to Engels in reply. Nevertheless, he insisted, “your satisfaction up to now is more important to me than anything the rest of the world may say of it”.  At the end of it all Marx was in no doubt about his debt to Engels. He wrote:
Without you, I would never have been able to bring the work to completion, and I assure you, it has always weighed on my conscience like an Alp that you have dissipated your splendid energy and let it rust on commercial matters, principally on my account, and into the bargain, still had to participate vicariously in all my minor troubles. 
In this Marx was undoubtedly right, and not just about his debt to Engels. He was right in his assessment of the terrible cost to Engels’ intellectual output during the years in which he worked in Manchester. Although he never complained, Engels knew it too – as is confirmed by the image left to us by Marx’s daughter of Engels joyously coming home from the factory after his last day’s work. When Engels was able to retire he could once again publish major works.
Levine argues that Marx’s death left Engels free to publish his distorted version of Marxism. But even the chronology of publication which Levine gives undermines his own argument. Anti-Dühring was not only published during Marx’s lifetime, the whole project was Marx’s idea. Moreover, Engels read the entire manuscript to Marx and Marx himself wrote one of the chapters on economics. The idea behind the book was to give a defence of Marx’s ideas, so it is hardly likely that such an obviously programmatic statement of his views would have been published without his complete agreement. As Engels noted, “it was self-understood between us that this exposition of mine should not be issued without his knowledge”.  Socialism, Utopian and Scientific was extracted from Anti-Dühring and also published before Marx’s death. The Origin of the Family, Private Property and the State appeared after Marx’s death, but was composed by Engels using the ethnographical notebooks which Marx had written. Ludwig Feuerbach was also published after Marx died but, as if to stress the continuity of the ideas expressed in it with the views of Marx and Engels’ first writings, Engels published Marx’s newly discovered Theses on Feuerbach as an appendix. Engels obviously saw no contradiction between the “humanist” young Marx and the “determinist” older Engels, otherwise he would scarcely have risked such a course, going so far as to describe the Theses as “the brilliant germ” of historical materialism.
Finally, The Dialectics of Nature, which is often used to support distortions of Engels’ work, was never intended for publication and actually bore the inscription, “All this to be revised”, almost as if it were a warning to those who were to take every last word as a finished, polished formulation. Nevertheless, the broad sweep of Engels’ intention was clear from Anti-Dühring, which was written at the same time.
On the key issue of whether Marx endorsed the idea of a dialectic in nature there can be little doubt. In Anti-Dühring Engels specifically quoted Marx’s Capital to this effect: “Here, as in natural science, is shown the correctness of the law discovered by Hegel in his Logic, that merely quantitative changes beyond a certain point pass into qualitative differences.”  And Marx goes on to say in a footnote that: “the molecular theory of modern chemistry ... rests on no other law”.  Marx himself had earlier drawn Engels’ attention to these passages in Capital, explicitly stating his belief that dialectical laws were in evidence in natural science: “in that text I quote Hegel’s discovery regarding the law that merely quantitative changes turn into qualitative changes and state that it holds good alike in history and natural science”.  Also in Capital Marx described exchange relations as operating like “a determining law of nature”. And, despite Carver’s claim that Engels’ admiration for Darwin is evidence of his inclination toward the model of natural science, Marx shared Engels’ assessment: “Darwin’s book is very important and it suits me well that it supports the class struggle in history from the point of view of natural science.” 
So the idea that Marx and Engels developed along separate theoretical paths finds little support in the biographical evidence. Naturally, the rough division of labour which they evolved led to different emphases. Equally naturally, they stressed different aspects of the theory depending on whether they were arguing against empiricists or idealists, system builders or vulgar economists, anarchists or reformists. But in all essentials they were at one. Perhaps nothing conveys this fact as forcefully as the testimony of Laura Marx’s husband, Paul Lafargue:
Engels was, so to speak, a member of the Marx family. Marx’s daughters called him their second father: He was Marx’s alter ego ...
... From their youth they developed together and parallel to each other, lived in intimate fellowship of ideas and feelings and shared the same revolutionary agitation: as long as they lived together they worked in common ... But after the defeat of the 1848 Revolution Engels had to go to Manchester, while Marx was to remain in London. Even so, they continued their common intellectual life by writing to each other almost daily ... As soon as Engels was able to free himself from his work he hurried from, Manchester to London, where he set up his home only ten minutes away from his dear Marx. From 1870 to the death of his friend, not a day went by but the two men saw each other, sometimes at one’s house, sometimes at the other’s ...
Marx appreciated Engels’ opinion more than anybody else’s, for Engels was the man he considered capable of being his collaborator. For him Engels was his whole audience. No effort could have been too great for Marx to convince Engels and win him over to his idea. For instance, I have seen him read whole volumes over and over to find the fact which he needed to change Engels’ opinion on some secondary point ... It was a triumph for Marx to bring Engels round to his opinion.
Marx was proud of Engels. He took pleasure in enumerating to me all his moral and intellectual qualities ... He admired the versatility of his knowledge and was alarmed that the slightest thing should befall him ... 
Marx and Engels were inevitably prey to the limitations of their age. They could not foresee all that natural science would achieve or the problems that would arise in the course of the next century of class struggle. But it is their joint legacy, as the content of their work also demonstrates, on which modern socialism rests.