Against these two unilateral perceptions, which both led to a dead end - and the search for a “Great Teacher” or Supreme Saviour - Marx affirms in Thesis III: “The coincidence of the changing of circumstances and of human activity or self-change [Selbstveränderung] can be conceived and rationally understood only as revolutionary practice.” . In other words: in revolutionary practice, in collective emancipatory action, the historical subject – the oppressed classes - transforms simultaneously both material circumstances and its own consciousness.
Marx returns to these problems in The German Ideology (1846), writing the following: “this revolution is necessary, therefore, not only because the ruling class cannot be overthrown in any other way, but also because the class overthrowing it can only in a revolution succeed in ridding itself of all the muck of ages and become fitted to found society anew.” 
That means that revolutionary self-emancipation is the only possible form of liberation: it is only by their own praxis, by their experience in action, that the oppressed classes can change their consciousness, at the same time as they subvert the power of capital. It is true that in later texts - for example, the celebrated 1857 Preface to the Critique of Political Economy - we find a much more deterministic version, which regards the revolution as the inevitable result of the contradiction between the forces and relations of production; however, as his principal political writings attest, the principle of the self-emancipation of the workers continued to inspire his thought and his action.
It was Antonio Gramsci, in his Prison Notebooks in the 1930s, who used, for the first time, the expression “philosophy of praxis” to refer to Marxism. Some people claim that it was simply a trick to mislead his fascist jailers, who might be wary of any reference to Marx; but that does not explain why Gramsci chose this formula, and not another, such as “rational dialectic” or “critical philosophy”. In fact, with this expression he defines, in a precise and coherent way, what distinguishes Marxism as a specific world view, and dissociates himself, in a radical fashion, from positivist and evolutionist readings of historical materialism.
Few Marxists of the twentieth century were closer to the spirit of this Marxist philosophy of praxis as Rosa Luxemburg. Admittedly, she did not write philosophical texts, and did not work out systematic theories; as Isabel Loureiro correctly observes, “her ideas, dispersed in newspaper articles, pamphlets, speeches, letters (…) are much more immediate answers to the conjuncture than a logical and internally coherent theorisation”.  Nevertheless: the Marxian philosophy of praxis, which she interprets in an original and creative way, is the dominant current – in the electric sense of the word - of her work and her action as a revolutionary. But her thought is far from being static: it is reflexion in movement, which enriches itself with historical experience. We will try to reconstitute the evolution of her thought through some examples.
It is true that her writings are traversed by a tension between historical determinism - the inevitability of the collapse of capitalism - and the voluntarism of emancipatory action. That applies in particular to her early works (before 1914). Reform or Revolution (1899), the book thanks to which she became known in the German and international workers’ movement, is an obvious example of this ambivalence. Against Bernstein, she proclaims that the evolution of capitalism necessarily leads towards the collapse (Zusammenbruch) of the system, and that this collapse is the historical road which leads to the realization of socialism. This amounts, in the final analysis, to a socialist variant of the ideology of inevitable progress which has dominated Western thought since the Enlightenment. What saves her argument from a fatalistic economism is the revolutionary pedagogy of action: “in the course of the long and stubborn struggles, the proletariat will acquire the degree of political maturity permitting it to obtain in time a definitive victory of the revolution.” 
This dialectical conception of education through struggle is also one of the main axes of her polemic with Lenin in 1904: “The proletarian army is recruited and becomes aware of its objectives in the course of the struggle itself. The activity of the party organization, the growth of the proletarians’ awareness of the objectives of the struggle and the struggle itself, are not different things separated chronologically and mechanically. They are only different aspects of the same struggle”. 
Of course, recognizes Rosa Luxemburg, the class can be mistaken during this combat, but, in the final analysis, “Historically, the errors committed by a truly revolutionary movement are infinitely more fruitful than the infallibility of the cleverest Central Committee”. The self-emancipation of the oppressed implies the self-transformation of the revolutionary class through its practical experience; this, in its turn, produces not only consciousness – a traditional theme of Marxism - but also will: “The international movement of the proletariat toward its complete emancipation is a process peculiar in the following respect. For the first time in the history of civilization, the people are expressing their will consciously and in opposition to all ruling classes. (…).Now the mass can only acquire and strengthen this will in the course of day-to-day struggle against the existing social order – that is, within the limits of capitalist society.” 
One could compare the vision of Lenin with that of Rosa Luxemburg with the following image: for Vladimir Ilyich, editor of the newspaper Iskra, the revolutionary spark is brought by the organized political vanguard, from the outside towards the interior of the spontaneous struggles of the proletariat; for the Jewish/Polish revolutionary, the spark of consciousness and revolutionary will ignites in the struggle, in the action of masses. It is true that her conception of the party as organic expression of the class corresponds more to the situation in Germany than to Russia or Poland, where already the question of the diversity of parties defining themselves as socialist was posed.
The revolutionary events of 1905 in the Tsarist Russian Empire largely confirmed Rosa Luxemburg in her conviction that the process of the development of consciousness by the working masses resulted less from the educational activity – Aufklärung – of the party than from the experience of the direct and autonomous action of the workers: “The sudden general rising of the proletariat in January under the powerful impetus of the St. Petersburg events was outwardly a political act of the revolutionary declaration of war on absolutism. But this first general direct action reacted inwardly all the more powerfully as it for the first time awoke class feeling and class-consciousness in millions upon millions, as if by an electric shock. (…) Absolutism in Russia must be overthrown by the proletariat. But in order to be able to overthrow it, the proletariat requires a high degree of political education, of class-consciousness and organisation. All these conditions cannot be fulfilled by pamphlets and leaflets, but only by the living political school, by the fight and in the fight, in the continuous course of the revolution.” 
It is true that the polemical formula on “pamphlets and leaflets” seems to underestimate the importance of revolutionary theory in the process; besides, the political activity of Rosa Luxemburg, which consisted, to a considerable degree, of writing newspaper articles and pamphlets – not to mention her theoretical works in the field of political economy - shows, without any doubt, the decisive significance that she attached to theoretical work and to political polemics in the process of preparing the revolution.
In this famous pamphlet of 1906 on the mass strike, the Polish revolutionary still uses the traditional deterministic arguments: the revolution will take place “following the need for a natural law”. But her concrete vision of the revolutionary process coincides with Marx’s theory of revolution, as he presented it in The German Ideology (a work which she did not know, since it was published only after her death): revolutionary consciousness can only become generalised in the course of a “practical” movement, the “massive” transformation of the oppressed can be generalised only during the revolution itself.
The category of praxis - which is, for her as for Marx, the dialectical unity between the objective and the subjective, the mediation by which the class in itself becomes the class for itself - allows her to overcome the paralysing and metaphysical dilemma of German social democracy, between the abstract moralism of Bernstein and the mechanical economism of Kautsky: whereas, for the former, the “subjective” transformation , moral and spiritual, of “human beings” is the condition for the advent of social justice, for the latter, it is the objective economic evolution which leads “inevitably” to socialism. That enables us to better understand why Rosa Luxemburg was opposed not only to the neo-Kantian revisionists, but also, from 1905 onwards, to the strategy of the passive “wait-and-see policy” defended by what was called the “orthodox centre” of the party.
This same dialectical vision of praxis also enabled her to overcome the traditional dualism incarnated in the Erfurt Programme of the SPD, between reforms, or the “minimum programme”, and the revolution, or “the final goal”. By the strategy of the mass strike in Germany which she proposed in 1906 - against the trade-union bureaucracy - and in 1910 - against Karl Kautsky - Rosa Luxemburg outlined a road that was capable of transforming economic struggles or the battle for universal suffrage into a general revolutionary movement.
Contrary to Lenin, who distinguished “trade-union consciousness” from “social democratic (socialist) consciousness”, she suggested a distinction between latent theoretical consciousness, characteristic of the workers’ movement during periods of domination of bourgeois parliamentarism, and practical and active consciousness, which emerges during the revolutionary process, when the masses themselves - and not only members of parliament and party leaders - appear on the political stage; it is thanks to this practical-active consciousness that the least organized and most backward layers can become, in a period of revolutionary struggle, the most radical element. From this premise flows her critique of those who base their political strategy on an exaggerated estimation of the role of organization in the class struggle - which is generally accompanied by an underestimation of the unorganized proletariat - forgetting the pedagogical role of revolutionary struggle: “Six months of a revolutionary period will complete the work of the training of these as yet unorganised masses, which ten years of public demonstrations and distribution of leaflets would be unable to do”. 
Was Rosa Luxemburg therefore spontaneist? Not quite… In the pamphlet The Mass Strike, the Political Party and the Trade Unions (1906) she insisted, referring to Germany, that the role of “the most enlightened, most class-conscious vanguard” is not to wait “in a fatalist fashion”, until the spontaneous popular movement “falls from the clouds”. On the contrary, the function of this vanguard is precisely “hasten (vorauseilen) the development of things and endeavour to accelerate events”.  She recognizes that the socialist party must take the political leadership of the mass strike, which consists of “informing the German proletariat of their tactics and aims in the period of coming struggle”; she goes so far as to proclaim that the socialist organization is the “vanguard of the entire body of the workers” and that “the political clarity, the strength, and the unity of the labour movement flow from this organisation”. 
It should be added that the Polish organization led by Rosa Luxemburg, the Social Democratic Party of the Kingdom of Poland and Lithuania (SDKPiL), clandestine and revolutionary, resembled the Bolshevik Party much more than it resembled German social democracy… Finally, an aspect that is often ignored must be taken into account: it concerns the attitude of Rosa Luxemburg towards the International (especially after 1914), which she conceived of as a centralized and disciplined world party. It is not the least of ironies that Karl Liebknecht, in a letter to Rosa Luxemburg, criticized her conception of the International as being “too mechanically centralised”, with “too much `discipline’, not enough spontaneity”, considering the masses “too much as instruments of action, not as having their own will; as instruments of action desired by and decided on by the International, not as desiring and deciding themselves” .
Parallel to this activist voluntarism, the determinist (economic) optimism of the theory of Zusammenbruch, the collapse of capitalism, victim of its contradictions, does not disappear from her writings, on the contrary: it is at the very centre of her great economic work, The Accumulation of Capital (1911). It was only after 1914, in the pamphlet The Crisis of Social Democracy, written in prison in 1915 - and published in Switzerland in January 1916 under the pseudonym “Junius” - that this traditional vision of the socialist movement at the beginning of the century was to be transcended. This document, thanks to the expression “socialism or barbarism” marks a turning-point in the history of Marxist thought. Curiously, the argument of Rosa Luxemburg starts by referring to the “objective laws of historical development”; she recognizes that the action of the proletariat “contributes to determining history”, but seems to believe that it is only a question of accelerating or delaying the historical process. So far, nothing new!
But in the following lines she compares the victory of the proletariat to “a leap of humanity from the animal world into the realm of freedom”, while adding: this leap will not be possible “until the development of complex material conditions strikes the incendiary spark zündende Funke of conscious will in the great mass”. We find here the celebrated Iskra, the spark of revolutionary will which is able to make the dry powder of material conditions explode. But what does this zündende Funke produce? It is only thanks to a “long chain of violent tests of strength” that “The international proletariat under the leadership of the Social Democrats will thereby learn to try to take its history (Seine Geschichte) into its own hands…” . In other words: it is in the course of practical experience that the spark of the revolutionary consciousness of the oppressed and exploited ignites.
By introducing the expression socialism or barbarism, “Junius” referred to the authority of Engels, in a writing going back “forty years” - undoubtedly a reference to Anti-Dühring (1878): “Friedrich Engels once said: ´Bourgeois society stands at the crossroads, either transition to socialism or regression into barbarism´.”[Ibid.] In fact, what Engels wrote is quite different: “both the productive forces created by the modern capitalist mode of production and the system of distribution of goods established by it have come into crying contradiction with that mode of production itself, and in fact to such a degree that, if the whole of modern society is not to perish, a revolution in the mode of production and distribution must take place”. 
The argument of Engels - primarily economic, and not political, like that of “Junius” - is rather rhetorical, a kind of reductio ad absurdum of the need for socialism, if we want to avoid the “destruction” of modern society - a vague formula: it is not easy to see exactly what it encompasses. In fact, it is Rosa Luxemburg who invented, in the strong sense of the word, the expression “socialism or barbarism”, which was to have such a great impact in the course of the twentieth century. If she refers to Engels, it is perhaps to try to give more legitimacy to a fairly heterodox thesis. Obviously it was the world war, and the collapse of the international workers’ movement in August 1914, that ended up by shaking her conviction of the inevitable victory of socialism. In the following paragraphs “Junius” developed her innovating point of view: “Today, we face the choice exactly as Friedrich Engels foresaw it a generation ago: either the triumph of imperialism and the collapse of all civilization as in ancient Rome, depopulation, desolation, degeneration – a great cemetery. Or the victory of socialism, that means the conscious active struggle of the international proletariat against imperialism and its method of war. This is a dilemma of world history, an either/or; the scales are wavering before the decision of the class-conscious proletariat”. 
We can discuss the significance of the concept of “barbarism”: it is is undoubtedly a question of a modern, “civilized” barbarism - thus the comparison with ancient Rome is not very relevant - and in this case what was affirmed in the Junius pamphlet turned out to be prophetic: German fascism, supreme demonstration of modern barbarism, could seize power thanks to the defeat of socialism. But what is most important in the formula “socialism or barbarism” is the term “or“: what is involved is the recognition that history is an open process, that the future is not yet decided - by “the laws of history” or the economy - but depends, in the final analysis, on “subjective” factors: consciousness, decision, will, initiative, action, revolutionary praxis. It is true, as Isabel Loureiro underlines in her very fine book, that even in the Junius pamphlet - as in later texts of Rosa Luxemburg - we still find references to the inevitable collapse of capitalism, the “dialectic of history” and the “historical need for socialism”.  But in the final analysis, the formula “socialism or barbarism” provides the foundations of another conception of the “dialectic of history”, distinct from economic determinism and the illuminist ideology of inevitable progress.
We find again the philosophy of praxis in the middle of the polemic in 1918 on the Russian Revolution - another capital text written behind bars. The essential thread of this document is well-known: on the one hand, support for the Bolsheviks, and their leaders, Lenin and Trotsky, who saved the honour of international socialism, by daring to make the October Revolution; on the other, a whole series of criticisms of which some - on the land question and the national question - are quite debatable, while others - the chapter on democracy - appear prophetic. What worries the Jewish/Polish/German revolutionary is above all the suppression, by the Bolsheviks, of democratic liberties - freedom of the press, of association, of assembly - which are precisely the guarantee of the political activity of the working masses; without them “the rule of the broad masses of the people is entirely unthinkable”.
The gigantic tasks of the transition to socialism “which the Bolsheviks have undertaken with courage and determination” - cannot be carried out without “the most intensive political training of the masses and the accumulation of experience”, which is not possible without democratic liberties. The construction of a new society is virgin terrain which poses “a thousand problems” that are unforeseen; however, “Only experience is capable of correcting and opening new ways.” Socialism is a historical product “born out of the school of its own experiences”: the whole of the popular masses (Volksmassen) must take part in this experience, otherwise “socialism will be decreed from behind a few official desks by a dozen intellectuals”. For the inevitable errors of the transition process the only remedy is revolutionary practice itself: “the only healing and purifying sun is the revolution itself and its renovating principle, the spiritual life, activity and initiative of the masses which is called into being by it and which takes the form of the broadest political freedom”. 
This argument is much more important than the debate on the Constituent Assembly, on which the “Leninist” objections to the text of 1918 have been concentrated. Without democratic liberties the revolutionary praxis of the masses, popular self-education through experience, the self-emancipation of the oppressed, and the exercise of power itself by the working class are impossible. Georg Lukacs, in his important essay “The Marxism of Rosa Luxemburg” (January 1921), showed with great acuity how, thanks to the unity of theory and praxis - formulated by Marx in his Theses on Feuerbach – the great revolutionary had succeeded in overcoming the dilemma of the impotence of social democratic movements, “the dilemma created by the pure laws with their fatalism and by the ethics of pure intentions”. What does this dialectical unity mean? “We have seen that the proletariat as a class can only conquer and retain a hold on class consciousness and raise itself to the level of its – objectively-given – historic task through conflict and action. It is likewise true that the party and the individual fighter can only really take possession of their theory if they are able to bring this unity into their praxis” .
It is therefore surprising that, hardly one year later, Lukacs wrote the essay - which would also appear in History and Class Consciousness (1923) - entitled “Critical Observations on Rosa Luxemburg’s ‘Critique of the Russian Revolution’“ (January 1922), which rejects en bloc the whole of the dissenting comments of the founder of the Spartacus League, claiming that she “imagines the proletarian revolution as having the structural forms of bourgeois revolutions”  - a not very credible accusation, as Isabel Loureiro demonstrates.  How can we explain the difference, in tone and content, between the essay of January 1921 and that of January 1922? A rapid conversion to orthodox Leninism? Perhaps, but more probably the position of Lukacs in relation to the debates within German Communism. Paul Levi, the principal leader of the KPD (Communist Party of Germany), had opposed the “March Action” of 1921, a failed attempt at a communist rising in Germany, supported with enthusiasm by Lukacs (but criticized by Lenin…); expelled from the Party, Paul Levi decided in 1922 to publish the manuscript of Rosa Luxemburg on the Russian Revolution, which the author had entrusted him with in 1918. The polemic of Lukacs with this document is also, indirectly, a settling of accounts with Paul Levi.
In fact, the chapter on democracy of this document by Luxemburg is one of the most important texts of Marxism, of communism, of critical theory and of the revolutionary thought of the twentieth century. It is difficult to imagine a refounding of socialism in the twenty-first century which does not take into account the arguments developed in these feverish pages. The most lucid representatives of Leninism and Trotskyism, such as Ernest Mandel and Daniel Bensaïd, recognized that this 1918 criticism of Bolshevism, concerning the question of democratic liberties, was in the final analysis justified. Of course, the democracy to which Rosa Luxemburg refers is that exercised by the workers in a revolutionary process, and not the “low intensity democracy” of bourgeois parliamentarism, in which the important decisions are taken by bankers, contractors, soldiers and technocrats, free from any popular control. The zündende Funke, the incendiary spark of Rosa Luxemburg, glowed one last time in December 1918, when she addressed the Founding Congress of the KPD (Spartacus League).
Admittedly, we still find in this text references to the “the law of the necessary objective development of the socialist revolution”, but it is really about “the bitter experience” that the various forces of the workers’ movement must go through before finding the revolutionary road. The last words of this memorable speech are directly inspired by the perspective of the self-emancipatory praxis of the oppressed: “The masses must learn how to use power by using power. There is no other way to teach them. Fortunately, we have gone beyond the days when it was proposed to “educate” the proletariat socialistically. Marxists of Kautsky’s school still believe in the existence of those vanished days. To educate the proletarian masses socialistically meant to deliver lectures to them, to circulate leaflets and pamphlets among them. No, the school of the socialist proletariat doesn’t need all this. The workers will learn in the school of action. (zur Tat greifen)”. Here Rosa Luxemburg refers to a famous formula of Goethe, Am Anfang war die Tat!. At the beginning of all is not the Word but the Action! In the words of the Marxist revolutionary: “Our motto is: In the beginning was the act. And the act must be that the workers’ and soldiers’ councils realize their mission and learn to become the sole public power of the whole nation”.  A few days later, Rosa Luxemburg would be assassinated by the paramilitary Freikorps - mobilized by the social democratic government, under the authority of the Minister Gustav Noske, against the rising of the workers of Berlin.
Rosa Luxemburg was not infallible, she made mistakes, like any human being and any activist, and her ideas do not constitute a closed theoretical system, a dogmatic doctrine which could be applied to any place and any time. But undoubtedly her thought is an invaluable source of inspiration to try to dismantle the capitalist machine and think of radical alternatives. It is not an accident that it has become, in recent years, one of the most important references in the debate, in particular in Latin America, on a socialism of the twenty-first century, capable of going beyond the impasses of the experiences conducted in the name of socialism in the last century – both social democracy and Stalinism. Her conception of a socialism that is both revolutionary and democratic - in irreconcilable opposition to capitalism and imperialism - based on the self-emancipatory praxis of the workers, on self-education through experience and on the action of the great popular masses thus becomes strikingly topical. The socialism of the future will not be able to do without the light from this glowing spark.