Notes on Postmodern Architecture
Tom Hicks
primary source is Powell.
 

In modernist Architecture, function dictates form.  It is genometry with no frills.  Beauty is in the fact that the geometry in the building reflects the
"natural laws".... no-ornamentation.  Just cubes and triangles.  The manifesto
of this era is "Towards a New Architecture" (1927) by LeCorbusier (1887-1965)
who is famous for saying "Nevermore" - ... Never any more garlands,
exquisite ovals, budoirs embellished with poofs of gold... no more
stiffling elegancies.... This became known as International Style  It celebrated
the "rational" in creations that should exhibit a grandeur of a mathamatical order... for in turning to mathamatical calculations it would reveal
universal law - the principles that govern the universe.... these designs
should be intelligent, cold and calm.... pure creations of the mind in
harmony with natural laws."

By the 1950's International Style was dominating....but what it all boiled down to was cityscapes full of concrete and glass boxes... perfectly geometrical and perfectly alienating of humaness. Pomo architecture began showing up in the  60's but the first book to thematasize pomo architecture was by Charles Jencks  "The Language of Postmodern Architecture" (1977/1991).

Here is Jencks quoting Humberto Eco:  
 

The postmodern reply to the modern consists of recognizing that the past, since it cannot really be destroyed, because its destruction leads to silence, must be revisitied; but with irony, not innocently.  I think of the postmodern attitude as that of a man who loves a very cultivated woman and knows he cannot say to her, 'I love you madly', because he knows that she knows (and that she knows that he knows) that these words have already been written by Barbara Cartland.  Still, there is a solution.  He can say, "As Barbara Cartland would put it, 'I love you madly'.  At this point, having avoided false innocence, having said clearly that it is no longer possible to speak innocently, he will nevertheless have said what he wanted to say to the woman: the 'he loves her madly', but he loves her in an age of lost innocence.  If the woman goes along with this, she will have recieved a declaration of love all the same.
Neither of the two speakers will feel innocent, both will have accepted the challenge of the past, of the already said, which cannot be eliminated; both will consciously and with pleasure play the game of irony... But both will have succeeded, once again, in speaking of love.

What pomo architecture does is called by Jencks "double coding."  For Jencks builidings signify.  They can be read like a book.  When a building has double coding (says two or more things simultaneously that are contradictory, and even mocks or refers back to itself paradoxically) then this is pomo architecture.

An excellent example is the AT&T building.  It is a sky-scraper in the
shape of a grand-father clock.  The building connects with us in a familiar way
instead of being just a "glass and steel box".... the buiding also says
grandfather clock.  There is double coding however through the juxtapostion
of styles.... grandfather clock and moderninst skyscaper - so that irony,
ambiguity, and contradiction emerge.... this architecture says
"both/and".   By combining the contemporary (skyscraper) with the antique
(grandfather clock)  and the functional/modernist (steel and glass boxes)
and the decorative (a chippendale broken pediment) this building can mean
many things all at once, and it is self-conscious of this, not innocent in its self-signification (as Eco's lover).  Nevertheless it is effective in
communicating with us because of it's own ironic self acceptance of all
that has come before it.  And it is aware that there is "no center" (after the
fall of grandnarratives ) and so why not fill it with a clock.
 

Eco, Umberto (1984). Postscript to the Name of the Rose (New York and London: Harcourt Brace Jovanovich, 1984)

Jencks, Charles (1991).. The language of post-modern architecture / Charles Jencks.  6th ed.  London : Academy Editions, 1977 original edition.

Le Corbusier.  (1927). Towards a new architecture,.  New York, Payson & Clarke, ltd.

Powell, Jim -  Postmodernism for Beginners (Writers and Readers Inc., 1998)