Luhmann said he was surprised that his work had been associated with postmodern theory because his work is quite different. In his 1995 lecture on “Systems Theory and Postmodernism,” Luhmann speaks of various “symbolizations of of unity.” These symbolizations make life meaningful or somehow help to orient society on a large scale.
In “premodern” times, people believed that human life or society was part of nature. In nature we see hierarchy as, for example, when one kind of animal preys on other animals and plants. Thus, more powerful humans can use and exploit less powerful people—and these people were intended by nature to be more or less powerful. For Aristotle, there were natural slaves.
Luhmann traces a history of modernity beginning in the 17th century with the loss of the faith in the unity of nature and society, or the old belief that social structures reflect natural laws, as in “natural” hierarchies. The notion that society was by nature hierarchical had to be dropped. The traditional authorities—religious and secular—were seen to be fallible. Martin Luther attacked the authority of the Catholic Church, replacing it with a close reading of scripture. Theologians started using reason to argue for various interpretations of scripture, thus the birth of hermeneutics. Disputed questions (quaestiones disputatae) were no longer decided by a religious authority. And legal questions could not be arbitrarily decided by a king; legal decisions had to grounded in the law, which was preserved in printed books, and even kings were bound by these laws.
According to Luhmann, the old belief in nature was first replaced by the concept of happiness–that everyone could be happy as long as they were satisfied with their condition and accepted certain constraints. A commoner might be happier than a nobleman. Consider John Milton’s words:
The mind is its own place, and in it selfParadise Lost, Book 1
Can make a Heav’n of Hell, a Hell of Heav’n.
This capacity for happiness/unhappiness unified or equalized people, in theory anyway. But this ideology didn’t last. In the 19th century, happiness—“the pursuit of happiness”—was replaced by solidarity, as individuals needed to work together rather than just seeking personal happiness. This first appeared in the workers movements and seen most vividly in the revolutions of 1848. Society was no longer considered the sum total of individual happinesses–as in Jeremy Bentham and utilitarianism. This implies a shift from nature to morality, or a normative framework. A baseline of consensus is necessary. Durkheim is the key theorist here. In this view, each person has (or should have) a role to play, and each role comes with expectations. Education is largely about being trained for a role, or career. The role one plays might not produce individual happiness, but, if society is to endure, stable roles need to be filled—someone has to do the unpleasant or boring work. Duty takes precedence. Being a father, for instance, might not bring personal fulfillment but a man has to do his duty.
After solidarity came the active, reformist society that wanted to alleviate the suffering of the poor and excluded. Equality was the keyword; and “good” people tried to lift up others rather that just thinking about themselves or their social class or other group affiliation—solidarity. This was the Progressive Era (1890s-WWI).
I don’t think these various symbolizations of unity have actually been replaced by the next one; rather, they have layered on top on one another. The olde symbolizations haven’t disappeared; they have often been absorbed into newer symbolizations.
Speaking at the end of the 20th century, Luhmann said that we have to accept a society without happiness, without solidarity, and without equality of living conditions. But I don’t think he actually meant there is no possibility at all for happiness, solidarity, or equality—at least on a limited scale. Universal equality and the rest are are no plausible notions. He was saying that these terms are no longer effective symbolizations of unity of society; they no longer serve as slogans to motivate society or provide meaning. So what we have to give up is the very idea of social unity. We have, instead, functional differentiation and a lot of fragmented subcultures with their own sources of information (thanks to the Internet) and their own narratives.
Regarding postmodernism, an important difference between postmodernism and Luhmannian theory is that for Luhmann society consists of communication only. And there has been no real postmodern break because society still consists of communication only. Luhmann speaks of modernity (beginning in late 17th century) rather than postmodernity. He also said that postmodern thinkers don’t have much to say about functional differentiation; the philosophical literature focuses mostly on semantics rather than social structures. But as he argues elsewhere, semantics reflects social structure.