The books offer a view of a human-centered universe, a view of order, in which the soul, or human feeling and the soul, play a central role.
Taken as a whole the four books create a sweeping new conception of the nature of things which is both objective and structural (hence part of science) - and also personal (in that it shows how and why things have the power to touch the human heart). A step has been taken, through which these two domains - the domain of geometrical structure and the feeling it creates - kept separate during four centuries of scientific thought, have finally been united.
There are thus two worlds in our minds. One is the scientific world which has been pictured through a highly complex system of mechanisms. The other is the world we actually experience. These two worlds, so far, have not been connected in a meaningful fashion. Alfred North Whitehead, writing about 1920, was one of the first philosophers to draw attention to this modern problem, which he called the bifurcation of nature. Whitehead believed that we will not have a proper grasp of the universe and our place in it, until the self which we experience in ourselves, and the machinelike character of matter we see outside ourselves, can be united in a single picture. I believe this. – Christopher Alexander, The Luminous Ground, p13
... It is this ongoing rift between the mechanical-material picture of the world (which we accept as true) and our intuitions about self and spirit (which are intuitively clear but scientifically vague) that has destroyed our architecture. It is destroying us, too (p18)
Those who are familiar with such matters will note that Alexander is describing an algorithm. The fundamental differentiating process is an outer loop, and the fifteen properties/transformations are primitives. Alexander treated the building site itself as an analog computer, using the information embedded in its current state at any moment to compute the next step in the process. In a way it reaches back to his earliest mathematical work, circumventing the problem of gathering and partitioning a snarl of design concerns, by performing the computation in situ.
In construction, the convention is that the blueprints are the supreme authority on whether or not this or that constituent of the process did their job. In many jurisdictions, this fact is actually enshrined in statute. Alexander’s method eschewed committing to the precise geometry of the intended outcome, because that was precisely what got revealed throughout his idiosyncratic construction process. In other words, any drawing of a building Alexander drew was only ever a suggestion. Subcontractors and planning authorities, accustomed to authoritative blueprints, simply couldn’t understand it.
It [APL] is a peculiar tome: a choose your own adventure for how to build a modern medieval city-state.