COMMUNISM means a classless society evolved on the ruins of capitalism (which is based on capitalist exploitation of wage labour). This is to be achieved by intensification of class struggle to the point of abolition of the two poles of the antagonism – capital and wage labour. Whenever and wherever communists participate in institutions of bourgeois democracy — e.g., the parliament — they do it exclusively with this end never for harmonising the interests of the opposing classes.

By contrast social democrats take such institutions “as a means, not of doing away with two extremes, capital and wage labour, but of weakening their antagonism and transforming it into harmony. However different the means proposed for the attainment of this end may be, however much it may be trimmed with more or less revolutionary notions, the content remains the same. This content is the transformation of society in a democratic way, but transformation within the bounds of petty-bourgeoisie.” (From The Eighteenth Brumaire of Louis Bonaparte by Karl Marx)

In a word, communism is essentially revolutionary : its adherents value reforms basically as stepping stones to revolution. Social democrats are essentially reformist : they advocate and work for reforms to prevent revolution. They cannot altogether avoid the hard reality of class struggle, but there they always seek to strike a compromise, to balance and “harmonise” the antagonistic interests. They thus work for preserving the capitalist social order, albeit in a more democratic, more civilised shape. This is where their petty-bourgeois outlook coincides with that of the more intelligent sections of the big bourgeoisie.

Thanks to this outlook and their stubborn struggle against revolutionary communists, social democrats earn the trust of the ruling bourgeoisie. In the face of crisis the latter sometimes allows or even supports social democratic parties to form governments in the existing parliamentary system and act as crisis managers on their behalf. Such governments play this role through state welfarism (providing reliefs) and by persuading the exploiters and the exploited to agree to a set of compromises (in the name of industrial peace and development, national interest etc.) so that class conflicts are kept within bounds and a revolutionary conflagration is avoided. In the process however, they get assimilated in bourgeois parliamentarism — in the capitalist system itself — and acquire all the vices of this system such as corruption, anti-people bureaucratic attitudes and so on. Such cases have been experienced in many a country; and also in our country at the slate level.

The essential difference between communism and social democracy does not however, always appear in a clear-cut manner. Social democratic trends often infiltrate into communist parties, because in real life the proletariat and the petty-bourgeoisie closely mix with each other. If this process of infiltration continues unopposed, a communist party may even become essentially social democratic while retaining its original sign board. In fact this is how social democracy has actually evolved in our country.