In their fundamental 1972 book Learning from Las Vegas, Robert Venturi, Denise Brown, and Steven Izenour developed these two categories from an intensive analysis of the Las Vegas strip to describe buildings and their relationship to an observer passing by at automotive speed.

Venturi et al. explored the techniques evolved by a generation of architects and designers in the advertising "arms race" between competing attractions on the Las Vegas strip. They found that these commercially motivated ornamentation techniques were able to generate interest (even in unpromising buildings) and they used what they learned to argue for the desirability of reimporting ornamentation (specifically, historically or socially allusive ornamentation) back into architecture after it had been shriven away by the purifying fires of modernism.

"Ducks" are buildings whose very shape are meant to portend the activity carried on within. The name implies the slightly (or more than slightly) ridiculous and comes from a famous duckoid building on Long Island housing an unpretentious restaurant specializing in poultry (see the URL below). Ducks in the generic sense aren't so common nowadays, at least in my experience. But it's easy to think of some close relatives, such as the venerable Brown Derby restaurant in Los Angeles, the occasional car outfitted as a giant hot dog and serving as a mobile hot dog stand, or a large concrete dinosaur in the desert. Venturi et al. did not find many ducks in Las Vegas, but they developed the category and kept it in reserve to make a point.

"Decorated sheds" are fairly mundane structures (hotels, restaurants, casinos, gas stations, etc.) where large-scale decorations, either as text (e.g., "McDonald's") or as obvious symbols (e.g., golden arches) tell the quickly-moving passerby what's afoot within these uninspiring boxes and in the best cases "warm the product" by generating enthusiasm or some other positive emotion the building itself cannot arouse. It was the myriad of decorated sheds on the strip that Learning from Las Vegas treated as a watershed of effective ornamentation techniques.

Venturi illustrated his argument in part with an analysis of his 1963 Guild House in Philadelphia (see URLs below), a relatively mundane retirement home whose ornamentation makes it (for Venturi) a decorated shed. While creating a functional, boxy six-storey building suited to its purpose, he subtly imbued it with historicizing ornamentation that adds meaning. Through the clever use of white-glazed bricks, placement of windows, and other devices, he suggested, in a highly attenuated form, a renaissance palazzo, giving a heroic scale, and by implication, a certain dignity to this retirement home (and that's not a bad thing).

He also created a giant column on the face of the building; almost an inside joke, the viewer has to have the wit to piece the column together mentally from a base of white-glazed bricks (surrounding the ground-level entrance), a column shaft suggested by voids in the facade created by recessed balconies rising up the center of the facade, and a capital formed by a large, almost palladian segmented-arc window directly above the "shaft." Venturi included the column because of the monumentality it connotes; but he can't for a minute be expected to take something as academic and old hat as the classical orders seriously, so he jokingly puts one giganterrific column on the facade which you need to decode. That's postmodernism in a nutshell, irony and all. On top was a funny sculpture of a nonfunctional gold-anodized TV antenna, standing for TV viewing--the god (or last refuge) of the immobile old (I'm not making this up: Venturi suggested that had the inhabitants not been Quakers, a large plaster sculpture of the Virgin Mary would have been appropriate). Venturi et al.:

But in Guild House, the symbolism of the ordinary goes further than this. The pretensions of the "giant order" on the front, the symmetrical, palazzolike composition with its three monumental stories (as well as its six real stories), topped by a piece of sculpture--or almost sculpture--suggest something of the heroic and the original. It is true that in this case the heroic and original facade is somewhat ironical, but it is this juxtaposition of contrasting symbols--the appliqué of one order of symbols on another--that constitutes for us the decorated shed.

Venturi doesn't like to be labelled as a postmodern architect. Nevertheless, having written Learning from Las Vegas some six years before postmodern architecture really took off in about 1980 and having designed Guild House some ten years before that, he adumbrated postmodernism by finding new ways through ornament to fill the vaccuum left by the sagging modernist project.

Appendix.

Charles Jencks wrote a funny critique of modern architecture in The Language of Post-Modern Architecture. He does not argue against the intellectual underpinnings of modernism so much as point to risible unintended results of eggheaded modern design. Because international style modernism (and its offshoots) avoided historicizing ornamentation, the acceptable decorative palette was rather limited, to abstract, preferably geometrical decoration and attractive materials which emphasized, or "articulated" how the structure had been put together. It was all about fiddling with proportions, meaningful mathematical resonances, showing the girders on the outside, and other not-too-obvious schemes. (Certain architectural historians went into transports over a corner design employing two I-Beams and an L-Beam in Ludwig Mies van der Rohe's 1947 Navy Building at the Illinois Institute of Technology. They even engaged in a scholarly debate over whether the corner treatment represented "endlessness" or "closedness." That's reading a lot into a couple of girders!)

Jencks argues that no matter how abstractly beautiful the concept on the architect's drawing board, real people in the real world will seek to impose meaning even where none is intended, like a Rorshach test (this is not a novel observation, of course). Among many examples, Jencks points to a darkly funny 1975 Old Age Home in Amsterdam by the capable modernist architect Herman Hertzberger. It is a clean design with white lines on the exterior demarcating the different apartments and thus forming a sort of square white grid over the black facade. Fair enough, all nice geometry. But Jencks points out that what people tend to see are a field of white crosses with black coffins between them--a pointed, unwelcome message in an old age home! Venturi et al. take a different tack:

When it cast out eclecticism, Modern architecture submerged symbolism. Instead, it promoted expressionism, concentrating on the expression of architectural elements themselves: on the expression of structure and function. It suggested, through the image of the building, reformist-progressive social and industrial aims that it could seldom achieve in reality. By limiting itself to strident articulations of the pure architectural elements of space, structure, and program, Modern architecture's expression has become a dry expressionism, empty and boring--and in the end, irresponsible. Ironically, the Modern architecture of today, while rejecting explicit symbolism and frivolous appliqué ornament, has distorted the whole building into one big ornament. In substituting "articulation" for decoration, it has become a duck.

URLs for illustrations.

Brown and Venturi: http://www.upenn.edu/almanac/v47/n19/FrenchCXN.html
The original duck
: www.metropolismag.com/html/vsba/robert_venturi.html (scroll down).
Venturi's schematic of a duck and a decorated shed: http://www.utexas.edu/coc/journalism/SOURCE/J395smF0/readings/flanamg3.jpg
Guild House photos: www.audc.org/expensive/tower/tower3.html
A renaissance palazzo: http://www.roma2000.it/zfarne.html
Venturi on Guild House: www.vsba.com/projects/fla_archive/20.html
Picture of Mies: http://www.achievement.org/achievers/joh0/large/joh0-019.jpg
Finickal Miesian corner detailing (not the corner mentioned in the text above): http://slate.msn.com/features/ChicagoArchitecture/14_Chicago-330.jpg
Jencks: http://www.artnet.com/magazine/news/TUCHMAN/Images/tuchman10-25-8.jpg

Bibliography.

Huxtable, Ada Louise, "Architecture in the 1970s," 42-44 in Kicked a Building Lately? (1976). Huxtable discusses Venturi's Guild House and Learning from Las Vegas.
Jencks, Charles, The Language of Post-Modern Architecture (5th edition, 1987). See esp. pp. 14-19 on Mies, 21 on Hertzberger's Old Age Home.
Lambert, Phyllis, "Forging a Language," 277-330 in Lambert, Phyllis, ed., Mies in America (2001). A sympathetic treatment of Mies's IIT designs.
Venturi, Robert, Brown, Denise Scott, and Izenour, Steven. Learning from Las Vegas (1972).
Venturi, Brown and Izenour, Learning from Las Vegas, revised edition (1977). The details of my discussion and quotations are drawn from this volume, pp. 87-103.