(From Jencks, Postmodernism: The New Classicism in Art and Architecture)
Jencks argues that postmodern architecture "contrast(s) with the older notion of classical rules in being understood as relative rather than absolute, responses to a world of fragmentation, pluralism and inflation rather than formulae to be applied indiscriminately." (330)
1. The most obvious new convention concerns beauty and composition. Instead of Renaissance harmony and Modernist integration, we have dissonant beauty or disharmonious harmony. In a new pluralist society an oversimplified unity is either false or unchallenging. The juxtaposition of tastes and world views is more real than modernism was prepared to allow. This also comes from contemporary science's conviction that the universe is dynamic and changing. Classical forms have mirrored a universe that was static and in harmony. The Renaissance gave us architecture that was well proportioned, on Greek lines, and mirrored the microcosm and the macrocosm. Now, we don't have any one theory of the microcosm that is "true".
2. Pluralism is also important. Stylistic variety is important, and the celebration of difference is always apparent. Different "languages" of art and architecture are mixed together. It is not just a matter of whim, but is tied to specific functions and symbolic intentions. Ambiguity is often valued – it is up to the reader to supply the "unifying text".
3. Postmodern architects try to achieve an urbane urbanism. New buildings should both fit into and extend the urban context, reuse such constants as the street, arcade and piazza, yet acknowledge too the new technologies and means of transportation. Elements of the city must be balanced – public to private, working to living, monument to infill, short blocks to city grid. This will end up looking more like the 18th century European city, where you have small blocks and mixed-use planning, rather than the modern overcentralised city.
4. Anthropomorphism is another important trait. Many postmodern architects incorporate ornaments and mouldings suggestive of the human body. There might be a hidden or suggested face, for instance, or a full figure.
5. Another theme is the continuum between the past and the present. Recall that for modernism there is a positive break with the past. In postmodern architecture there is parody, nostalgia, and pastiche. It is almost like a half-remembered dream – bits of classical reference. The technical term is "anamnesis" – suggested recollection, or unforgetting.
6. There is a kind of return to painting in postmodernism, although it is a return that does not simply replicate the modernist search for form. There is a return to content. There is no sense that we are looking for the pure "spiritual" form, but rather we are playing with the images of the past, without the narrative of the past.
7. Postmodernism uses double-coding, irony, ambiguity, and contradiction. The unexpected is incorporated. Opposites are juxtaposed.
8. When several codes are used coherently they produce another quality, multivalence. A univalent work or building attempts to refer only to itself. A multivalent building reaches out to the rest of its environment and makes different associations. This ensures that a work will have multiple resonances, and different readings.
9. This multivalence comes only with the displacement of conventions and the reinterpretation of tradition. A classical form may be pressed into new service, and look strange to begin with but actually make sense once you understand the references.
10. Postmodernists also try to elaborate new rhetorical figures.
11. Postmodernism finally has a return to an absent centre. It has always been linked with other "posts": post-western, post-Christian. It suggests a culture that has a sense of departure, but no clear sense of direction. We don't have any grand narratives anymore, but we are led back to ourselves and our "petit recit" through the work of the postmodernists. And, just as post-industrial incorporates the industrial as well (it is not a repudiation or abandonment), so the post-modern incorporates the modern as well.