Notes on the synthesis of form

is an excellent book by Christopher Alexander (isbn 0-674-62751-2). As usual I'm going to quote from a few pages:
Poincaré once said: "Sociologists discuss sociological methods; physicists discuss physics." I love this statement. Study of method by itself is always barren.
Culture is changing faster than it has ever changed before...what once took many generations of gradual development is now attempted by a single individual.
Modern mathematics deals at least as much with questions of order and relation as with questions of magnitude.
If the world were totally regular and homogeneous, there would be forces, and no forms. Everything would be amorphous. But an irregular world tries to compensate for its own irregularities by fitting itself to them, and thereby takes on form. D'Arcy Thompson has even called form the "diagram of forces" for the irregularities.
No complex adaptive system will succeed in adapting in a reasonable amount of time unless the adaptation can proceed subsystem by subsystem, each subsystem relatively independent of the others.
We define a concept in extension when we specify all the elements of the class it refers to. And we define a concept in intension when we try to explain its meaning analytically in terms of other concepts at the same level.
Design is by nature imaginative and intuitive.
Every form can be described in two ways: from the point of view of what it is, and from the point of view of what it does.
It is the culmination of the designer's task to make every diagram both a pattern and a unit. As a unit it will fit into the hierarchy of larger components that fall above it; as a pattern it will specify the hierarchy of smaller components which it itself is made of.
What is it about the internal structure of any problem that makes it hard to solve? In nine cases out of ten, we cannot solve it, because we cannot grasp it.