Modernism or Post-Modernism: How to Tell

I was talking to a friend about a book and how to place it in modernism or post-modernism, and she urged me to post my simple way of thinking about it here, so:

Quick version:

Modernism offers the simplest version.
Post-modernism is self-referential.

Long version with a couple of examples:

Modernism offers the simplest version - stripped down - with no embellishment or ornamentation. As Mies van der Rohe said, "Less is more." This is true of writing: think of Hemingway or Cormac McCarthy. It is true of art: think of Piet Mondrian at the beginnning, through Barnett Newman and up to recent post-minimalist Agnes Martin. In music, the ultimate and explicit practitioner is Schoenberg, whose 12-tone "...technique is a means of ensuring that all 12 notes of the chromatic scale are sounded as often as one another in a piece of music while preventing the emphasis of any...". In architectural design it is the Bauhaus movement, exemplified best by Mies himself.

Post-modernism is self-referential. We no longer need to use Samuel Taylor Coleridge's
...willing suspension of disbelief for the moment, which constitutes poetic faith.* There is no sense of disappearing into another world, another person's POV, no looking through an imaginary window. The creator is present at all times. Think of Jose Saramago, (in my mind THE most brilliant practitioner of post-modernism on the planet): he is always laughing there behind his narrator. The artist and his world are evident in the construction of the art. Installation art, performance art, conceptual art and multi-media art can fit into post-modernism. Post-modern art can include words, appropriated images and other popular culture references. Step up Jeff Koons, Cindy Sherman and Jenny Holzer, to be examples. Likewise for architecture: think of Michael Graves's jokey Dolphin and Swan hotels at Disney World - using references to historical architectural features - nothing to do with form following function, or the demands and/or opportunities of our era.

Post-modern music: not sure I know enough to say...requires some study and thought.

*from Biographia Literaria (1817)

The marigold asks nervously:
Does that help? Suggestions, anyone?