Pattern 240 - Half Inch Trim

It's a kind of bible of architecture, A Pattern Language came out in 1977, and in over 1,000 pages codifies the language of the built environment, or how it ought to be. It's a guide to livable cities and livable buildings. Maybe it's a bit Cali-centric, with all it's recommendations for outdoor space design, but it serves nonetheless as a builder's guide to making nice places to be in. 

The book is over 1,000 pages, and not until page 1,112 do we see Pattern 240 - Half Inch Trim. It is the most beautiful, simple, and airtight explanation in the whole book.

Pattern 240 - Half Inch Trim

Totalitarian, machine buildings do not require trim because they are precise enough to do without. But they buy their precision at a dreadful price: by killing the possibility of freedom in the building plan. 

A free and natural building cannot be conceived without the possibility of finishing it with trim, to cover up the minor variations which have arisen in the plan, and during its construction. p1112

The principle goes on to explain that it is essential that cuts be inaccurate within a half-inch or so, to avoid waste, but also to allow subtle adaptations.

And it goes on to explain why the modern practice of using precision building components is a bad idea:

"This one aspect of construction has by itself destroyed the builder's capacity to make a building which is natural, organic, and adapted to the site." p1113

But this is not the real argument for Half Inch Trim. The real argument is more deeply psychological, and underlies a quantitative, and universal, feature of aesthetic sensibility:

Our own bodies and the natural surroundings in which we evolved contain a continuous hierarchy of details, ranging all the way from the molecular fine structure to gross features like arms and legs (in our own bodies) and trunks and branches (in our natural surroundings).

We know from results in cognitive psychology that any one step in this hierarchy can be no more than 1:5, 1:7, or 1:10 if we are to perceive it as a natural hierarchy. We cannot understand a hierarchy in which there is a jump in scale of 1:20 or more. It is this fact which makes it necessary for our surroundings, even when man-made, to display a similar continuum of detail. 

Most materials have some kind of natural fibrous or crystalline structure at the scale of about 1/20 inch. But if the smallest building detail dimensions are of the order of 2 or 3 inches, this leaves a jump of 1:40 or 1:60 between these details and the fine structure of the material. ... [and 1/20 inch is 1:10 to a half inch] p1114-1115

Notes:
A Pattern Language - Towns, Buildings, Construction
Christopher Alexander, Sara Ishikawa, Murray Silverstein. Oxford University Press. New York. 1977.