Through the 1950s teens were taught that absolute truth and morality existed. Almost everyone believed in the traditional point of view and tried to live accordingly. 

By the 1970s teens were taught a relativist worldview. It said, “Truth exists, but you need to find it for yourself. No one can determine it for you.” Truth was no longer absolute but relative to you. Still, you were expected to find and live out a consistent and mostly traditional morality. 

Today’s teens grow up in a postmodern world. They are taught that there is no correct point of view. This shift has a powerful effect. It can kill the natural human instinct to search for truth. There is no truth, just opinion. You cannot tell if any opinion is more right than any other, and opinions are everywhere.

A teen’s parents say one thing, their favorite singer another, Hollywood a third, and their volleyball coach something else. Who is to decide?  Most teen’s own experience of life seems to validate a world of opinions devoid of truth. “What I felt was right last week doesn’t feel so right this week. Things have changed.” 

Truth has been demoted to opinion and opinion demoted to feelings. Reason has lost value.

Defining Postmodernism
Postmodernism defies definition intentionally. Defining it would violate one of its key principles: “no definite terms or absolute truths exist.” The assertion that “no truth exists” is a self-contradicting statement. In response, postmodernism says, “contradiction is unimportant.” 
The acceptance of contradiction is one of the most distinctive qualities of postmodernism.

In dismissing contradiction, postmodernism “justifies” never justifying anything. It also allows an odd answer to this question: Which of the following is the correct answer? 

1) Absolute truth exists 
2) Truth is relative to you
3) Truth does not exist 
4) All of the above.

At first, it would seem that postmodernism would answer 3) Truth does not exist, but in fact, the postmodern answer is 4) All the above are correct.
 
Postmodernism accepts the contradiction of answer 4. 

Thus, a politician can assert as a traditionalist that we should follow the Bible, yet live in open adultery as a relativist because marriage just isn’t working for him. As a postmodernist, he can dodge taking a stand by saying, “who am I to judge” and then pass laws he expects us all to follow as a traditionalist. 

In the postmodern world, we let him get away with the contradiction. 

Instability
Contradiction leads to instability of belief and morality, and instability is another characteristic of postmodernism. Oddly, instability is one of the most stable, reliable, and permanent things in modern life. Everything is subject to change, not just beliefs and morality, but also “place” and relationships. 

Today we move with ease and frequency from one place to another. We are not grounded geographically. Our ancestors were grounded in the village and it did not change very much. Then the old mom-and-pop restaurant by the oak tree was replaced by a Big Boy which has since become a MacDonald's. We have no stable geographical village.

We also have an unstable relational village. Neighbors move. We move. Siblings move. Youth have cousins they have never met, but might be having Thanksgiving dinner with their step-granddad and his unknown grandchildren. Best Friends Forever don’t last and families break down often.

Adolescence is a time of natural instability. Our ancestors went through it also, but they expected to become stable adults, with stable beliefs, in a stable village, and that all helped create a stable identity. That is not the case today. Instability is the new normal and that makes it even harder on teens.

Identity Issues
Jean Valjean, in Les Misérables, asks the question, “Who am I?” He is fighting to establish his identity as a man and not just a prisoner numbered 24601. 

But when the modern teen asks, "Who am I?" He answers, "Anyone I want to be!" 

Unlike Jean Valjean, who is trying to assert one, true, integrated, consistent identity, the modern teen juggles multiple identities with no felt need to integrate them. This reinforces a teen’s instability in faith, relationships, morals, emotions, and intellect. 

The result is long-term confusion (often unrecognized) and an inability to make commitments – one of the best ways to overcome instability. 

Postmodernism is a vicious circle, but if you ignore contradiction, the free floating world of youth makes a bit more sense.