One of the best-known early theories by Niklas Luhmann is his theory of trust. In his book, Vertrauen (1968), Luhmann presented his basic theses about trust. The function of trust is to reconstruct or to reduce the growing complexity of society.
Tag: Talcott Parsons
Shared opinions, values, purposes
Norms are a product of differentiation. Social systems differentiate expected behavior (norms) from actual behavior. That is to say, norms serve as prediction schemata. The norm is the expected. Behavioral norms are expected even if they are not anticipated. For instance, even if we know a person well and we anticipate that he will lie to us, we nonetheless expect him to tell the truth; otherwise we could not engage in communication with that person at all.
Social Systems Theory 