Folks like tomndebb and capybara seem to have more academically-grounded responses, so I would be inclined to follow what they say. Having said that, I humbly offer my take on the progression of art:
Primitive, Tribal - The rules for the art have not been fully formed and are not consistently adhered to (e.g., rhythm and harmony for music, perspective, color etc. for painting)
Classical - The rules are more or less mapped out and the emergence of true master practitioners of this defined art are identified.
Romantic - The rules are pushed and pulled and taken to fairly extreme places, but still adhered to.
Modern - The rules are broken, sometimes all at once, sometimes systematically over time - like jazz, moving through Dixieland, swing, bebop, hardbop, modal, and free jazz (simplified a ton, but you get the idea), where additional rules were broken every step of the way.
Postmodern - The rules are re-visited in a self-conscious way. The motive behind revisiting them depends on the artist - some, like the architect Capybara mentions, references the rules of architecture without basing the structure on the function behind those rules - he just did it to point out the rule. Others are trying to get back to simpler times when the rules mattered - a lot of punk bands these days want to be the indie cred bands of their childhood, but Nirvana happened and you can’t go back. And some artists just play with the rules - referencing them, mocking them, while at the same time exploiting them. I would say Madonna and some PoMo feminists, who argue for strength for women while utilizing traditional female stereotypes and sexuality for the eye-candy aspect of things (“My sleeping around is my control of my body!”) has a distinctly postmodern feel to it.
This is very simplified and just my $.02.