Postmodern architecture

It is difficult to differenciate postmodern and modern. Is time only the essense to it? From wikipedia :-

"Postmodernity or postmodern architecture is a period whose first examples are generally cited as being from the 1950's, which runs through the present. "

"Postmodernity in architecture is generally thought to be heralded by the return of "wit, ornament and reference" to architecture in response to the formalism of the International Style of modernism. " more to read ...