Engels discusses this topic in Chapter X, Part I of Anti-Dühring (Morality and Law. Equality). Engels discusses Dühring's method of analysis. Dühring thinks you break a subject down to its most simple components and then, using mathematical axioms, you can logically deduce what its true nature is. Engels calls this the A PRIORI method. In this method you logically deduce the nature of the object from its concept not from from the object itself. Then you reverse the process. You take your refurbished concept of the object and then judge the nature of the object by means of it instead of just studying the object itself. This is the garbage in, garbage out method.
In discussing "equality", Herr Dühring deduces the nature of society by logic "instead of from the real social relations of the people around him." He says the simplest form of society consists of just two people. Here you have two human wills and at this stage the two are ENTIRELY EQUAL to one another. From this Dühring says we can deduce "the development of the fundamental concepts of right." These two persons, by the way, are men.
Engels calls these two equal men "phantoms" because to be entirely equal they have to be free from any real life distinctions, including sexual distinctions and experiences, and thus become just abstract creations of Dühring's brain not real people at all.
Now what would justify one person becoming subordinate to another if they are entirely equal? Well if one of the two wills was, Engels explains, "afflicted with inadequate self-determination" then Dühring allows for its subordination. In other words the entirely equal wills are not entirely equal after all. Engels gives two more examples from Dühring in which "equality" will be replaced by inequality and subordination: they are "when two persons are 'morally unequal'" and when they are unequal mentally. Of course it is Herr Dühring and his followers who decide the moral and mental qualifications.
All this goes to show, Engels concludes, that Dühring has a shallow and botched outlook regarding the notion of equality. But this does not mean the idea of equality does not play "an important agitational role in the socialist movement of almost every country." The issue of Human Rights is the contemporary version of this debate. Following Engels, I will say that the "scientific content" of Human Rights will "determine its value for proletarian agitation."
The scientific content will be established by studying the history of the idea of Human Rights (AKA "equality.") It took thousands of years to get from the ideas about equality in the ancient world to those that the socialist movement holds, or should hold today. In the classical world of Greece and Rome inequality was as important as equality (slaves versus Roman citizenship for example).
Christianity recognized a form of equality-- all were equally subject to original sin. There was also, early on, the equality of the ELECT. But these were really bogus forms of equality as far as THIS world was concerned. Then, when the Germans overran the Roman Empire the ideals of human equality were set back for a thousand years due to the entrenchment of the FEUDAL ORDER.
Nevertheless, within that order a class was growing that would "become the standard- bearer of the modern demand for equality: the bourgeoisie." As a result of the maritime discoveries of the fifteenth century (da Gama, Columbus, etc.,) markets began to grow and the handicraft industries of the middle ages expanded into manufacturing concerns. This economic revolution took place within the political structure of feudalism. The bourgeoisie began to champion the notion of human rights and equality because human labor qua labor was seen as of equal value, a fact recognized in bourgeoisie political economy as the law of value "according to which," Engels writes, "the value of a commodity is measured by the socially necessary labour embodied in it." This connection was first brought to light by Marx in Das Kapital, Engels says.
The social contradiction between the new economic order of capitalism and the feudal political order brought about the great revolutions of the sixteenth and seventeenth centuries. Engels explains that "where economic relations required freedom and equality of rights, the political system opposed them at every step." It is interesting to note that the bourgeoisie was able to wrest power from the feudalists and is to day's dominant ruling class. The same contradiction on a higher level, this time between the working classes and the bourgeoisie, has not been resolved. But only a revolutionary transfer of political power to the workers can overcome the economic problems, as well as the social questions of war and imperialism, that mark the present period of bourgeoisie decline.
Engels points out that with the decline of the Roman Empire and the development of independent states each claiming the same rights to nationhood as the others, and being, in the bourgeois world at least, on similar levels of development, the notion of equality gave way to to that of universal human rights. That "universal human rights" are basically bourgeois rights is illustrated by the fact that "the American constitution, the first to recognize the rights of man, in the same breath confirms the slavery of the coloured races existing in America: class privileges are proscribed, race privileges sanctioned."
The logical extension of the call for the abolition of class privileges by the bourgeoisie is the working class' call for the abolition of classes themselves. There are two aspects to the demand for equally made by the working people. The first is a protest against the poverty and oppression of the workers as compared to the wealth and power of the rich. This first aspect is spontaneous and "is simply an expression of the revolutionary instinct" of oppressed people. The second aspect is derived from the bourgeoisie's own ideals and demand for equality in face of the feudal order and is put forth "in order to stir up the workers against the capitalists with the aid of the capitalists' own assertions." In both cases, according to Engels, the real demand of the workers is not class equality but the ABOLITION OF CLASSES. Any demand beyond [i.e., other than] that, he says, "passes into absurdity."
What Engels has tried to show is that our modern notions of human rights and of human equality are not eternal verities good for every time and clime. Both the bourgeois and proletarian versions are historical products. So are the views of the Taliban, for example, on the treatment of women and the rights of non Islamic people or those of some South Africans on the number of wives a man can have. These views as well as those we call "modern", by which we mean 'Western" in their capitalist or working class incarnations developed as a result of "definite historical conditions that in turn themselves presuppose a long previous history."
Those values, therefore, WE take for granted are the product of a specific historical trajectory in which they functioned to bring about and stabilize the world capitalist system. Engels says, quoting Marx, if the modern notion of human rights "already possesses the fixity of a popular prejudice" this is due to the continuing influence of the Enlightenment on our times. The task of socialists today is to agitate for truly effective universal human rights-- and these include the right to a living income, to health, to food, housing, education, and to live in a world at peace-- attainable once and for all through the abolition of classes.