While German theorist Karl Marx rarely used the term "class consciousness", he did make the distinction between "class in itself", which is defined as a category of people having a common relation to the means of production, and a "class for itself", which is defined as a stratum organized in active pursuit of its own interests.
Defining a person's social class can be a determinant for their awareness of it. Marxists define classes on the basis of their relation to the means of production – especially on whether they own capital. Non-Marxist social scientists distinguish various social strata on the basis of income, occupation, or status.
Early in the nineteenth century, the labels "working classes" and "middle classes" were already coming into common usage. "The old hereditary aristocracy, reinforced by the new gentry who owed their success to commerce, industry, and the professions, evolved into an "upper class". Its consciousness was formed in part by public schools (in the British sense where it refers to a form of private school) and Universities. The upper class tenaciously maintained control over the political system, depriving not only the working classes but the middle classes of a voice in the political process."
Class consciousness, as described by Georg Lukács's famous History and Class Consciousness (1923), is opposed to any psychological conception of consciousness, which forms the basis of individual or mass psychology (see Freud or, before him, Gustave Le Bon). According to Lukács, each social class has a determined class consciousness which it can achieve. In effect, as opposed to the liberal conception of consciousness as the basis of individual freedom and of the social contract, Marxist class consciousness is not an origin, but an achievement (i.e. it must be "earned" or won). Hence, it is never assured: the proletariat's class consciousness is the result of a permanent struggle to understand the "concrete totality" of the historical process.
According to Lukács, the proletariat was the first class in history that may achieve true class consciousness, because of its specific position highlighted in the Communist Manifesto as the "living negation" of capitalism. All others classes, including the bourgeoisie, are limited to a "false consciousness" which impedes them from understanding the totality of history: instead of understanding each specific moment as a portion of a supposedly deterministic historical process, they universalize it and believe it is everlasting. Hence, capitalism is not thought as a specific phase of history, but is naturalized and thought of as an eternal solidified part of history. Says Lukács, this "false consciousness", which forms ideology itself, is not a simple error as in classical philosophy, but an illusion which cannot be dispelled.