The free plan
After Mies van der Rohe’s Barcelona Pavilion (1929): a roof on a grid of cruciform steel columns, with walls placed freely beneath it.
The rules it illustrates
Less is more. Reduce a building to the fewest, most exactly made elements (a regular structure, a clear enclosure, an open and adaptable space) and let their proportion and detail carry the whole effect.
Where it appears in the book
In the styles Modernism.
In the chapters The Modern Movement.