Before the sixties, people used to find their safety in some persons of strong thoughts they saw as a leader, called authority.

Authority is a word  probably deriving from O. French "auctoritè" that means "prestige, right, dignity" and from the Latin "auctoritatem" and "auctor" that mean "command, master, author". Anyway it presents a person that is superior to another one.

In the sixties, a discussion about authority and about the facts making someone's authority. is developed.

A conclusion was that someone's authority is not made of his or her higher positions but it needs the recognition of his or her importance from the social group, because the more people are low literate the more he/she  has the necessity of an authority principle. In this period  the concern of authority is questioned and most people think that there cannot be any person to consider as authoritarian but rather  it is being authoritative what matters to meet the approval of the social group.

A doubt of the concern of authority also implies putting into question the concern of truth.There is not stable truth, stable meaning that was clear in the previous periods, for example (God in the Middle Ages). Instead of stable truth there is a series of questions and the postulate of the Postmodernism is that there is not truth and all science is based on it.

This also implies a turnover of traditional culture where signified was clear. So the Postmodernism art is mostly abstract and conceptual and there is no difference between low and high art, they come together in art production.  

The abstract art means that signified is not stabilized, but we are asked to give it. So in Postmodernism the reader in literature, the watcher in art, listener in music, has got an importance, because he gives the signified to work.