How was it that an invalid concept had become valid?

The concept of the Third Space is becoming widely used.

This concept will become as mainstream as democracy and human rights.

As strange and alien a concept as that has become.

"But the whole concept of peace studies has become much more middle of the road, less controversial."

Nonetheless, according to the show's organizers, the concept of time is becoming more popular.

This was long before the concept of preserving commercial vehicles had become established.

But the concept was becoming entrenched in the conservative agenda.

The trouble is that the concept has become too successful.

Over time, the concept has become broader and more sophisticated.