False universalization

Marx's historical materialist theory asserts that the "social, political and intellectual life" of an era is determined by and serves to facilitate the kinds of economic relations characteristic of that era. When the economic relations change, eg., from ancient to feudal or feudal to capitalist, those other elements change correspondingly.

He was frequently critical of bourgeois social theorists (especially some political economists) for having ignored  this dynamic. They assumed that certain human behavioural traits observable in their own place and time were part of a 'human nature' common to people everywhere and in all periods. Marx on the contrary thought that so-called human nature was malleable and had changed throughout history. The theorists were, in his view, erroneously universalising forms which were temporary, particular and contingent.

The alleged error can be regarded as an example of reification, the error of investing relations and concepts with more concreteness and objectivity than they in fact have.

Reification was extensively theorised by the Frankfurt School in the mid 20th century.

Horkheimer of the Frankfurt School in fact characterised all bourgeois science as 'reified ideology'.

In view of these concerns much of the output of the present day social sciences is problematical. Neoclassical economics, for example still takes homo economicus as its behavioural paradigm, regarding rationality, selfishness, and the "propensity to truck and barter" as the mainsprings of human motivation. Rational choice theory and game theory incorporate similar doubtful assumptions.

False universalization (the overgeneralisation of present behavioural traits) may be functional in maintaining the present form of social relations because it makes it appear as the only reasonable one, portraying alternatives as unrealistic because they call for different kinds of behaviour.

Marx's complaints
(A sample)

For each new class which puts itself in the place of one ruling before it, is compelled, merely in order to carry through its aim, to represent its interest as the common interest of all the members of society, that is, expressed in ideal form: it has to give its ideas the form of universality, and represent them as the only rational, universally valid ones. (The German Ideology, Chap. 1.) On leaving this sphere of simple circulation or exchange of commodities, which furnishes the "Free-trader Vulgaris" with his views and ideas, and with the standard by which he judges a society based on capital and wages, we think we see a change in the physiognomy of our dramatis personae. (Capital, v 1, c vi, last paragraph.) These formulæ, which bear it stamped upon them in unmistakable letters that they belong to a state of society, in which the process of production has the mastery over man, instead of being controlled by him, such formulæ appear to the bourgeois intellect to be as much a self-evident necessity imposed by Nature as productive labour itself. (Capital, v 1, c 1, s 4.) [B]y Classical Political Economy, I understand that economy which, since the time of W. Petty, has investigated the real relations of production in bourgeois society in contradistinction to vulgar economy, which deals with appearances only, ruminates without ceasing on the materials long since provided by scientific economy, and there seeks plausible explanations of the most obtrusive phenomena, for bourgeois daily use, but for the rest, confines itself to systematising in a pedantic way, and proclaiming for everlasting truths, the trite ideas held by the self-complacent bourgeoisie with regard to their own world, to them the best of all possible worlds. (Capital, v 1, c 1, s 4.) But it is quite impossible (to gain this insight) in the manner of those economists who obliterate all historical differences and who see in all social phenomena only bourgeois phenomena. If one knows rent, it is possible to understand tribute, tithe, etc., but they do not have to be treated as identical ( "Introduction" to A Contribution to the Critique of Pol. Econ., section: "The Method of Pol. Econ.") [H]e that would criticise all human acts, movements, relations, etc., by the principle of utility, must first deal with human nature in general, and then with human nature as modified in each historical epoch. Bentham makes short work of it. With the driest naiveté he takes the modern shopkeeper, especially the English shopkeeper, as the normal man. Whatever is useful to this queer normal man, and to his world, is absolutely useful. This yard-measure, then, he applies to past, present, and future (Capital, v 1, c xxiv, s 5.)