Summarising The properties of forms:
The 15 properties of forms describe the attributes we see in good and
wholesome compound objects in the physical world. They are interrelated and
cannot be considered distinct attributes of things but aspects of all well-formed
compounds.
In
— Christopher Alexander, The Center for Environmental Structure,
The Nature of Order, Book 1 [NoO1-01], p. 238.
For example, without strong centres, there can be no reference to the good shape of those centres. Local symmetries make little sense when you cannot differentiate, so depends on contrast. What is local about the symmetries is often defined by where it stands in levels of scale or relation to the void. Gradients imply a form can flow over a field connecting to not-separateness but also contrast. Boundaries and levels of scale imply centres and thus rely on strong ones to help define them. Contrast requires separation, so often implies boundaries or characterises the transformation of a gradient to a more explicit transition.
This interaction between the properties would be a weakness if they were building blocks of construction, but they are not. They are the properties of forms produced by taking natural steps of growth. They can be differentiating, extending, relaxing, defining, or refining. But they are never a mindless accretion of novelty or the result of top-down outside-in thinking.
These are all properties discernible when the growth process is a sequence of unfoldings punctuated with moments of relaxation. In effect, fully complete steps, including the moment to let things settle long enough to pick up on subtle hints to the best next direction.
Christopher Alexander connected the properties to natural processes[NoO1-01]. Gradients form as the ends of an element relax and regress to the mean of their surroundings. Levels of scale form as parts split, with some resultant sub-elements growing slower than others as things progress. Alternating repetition forms around weak sequences that collapse and pack into robust structural patterns through annealing or sliding into place. Roughness is recognising the negative, that purity and regularity often indicate a stress on surrounding forms. Boundaries appear by connective structure rather than allow for weak edges. Deep interlocks form when boundaries or contrasts fail to satisfy forces completely.
In effect, Alexander pointed out that all the properties are what we should expect when we grow a solution by the mechanisms natural to the physical world and when we allow it to form through a sequence of steps inspired by local revelation.
Can we use the properties to guide us when creating the sequence of actions we take? We can ask what is not quite right about the properties of our current forms. We can ask what feels stretched or underrepresented in the current configuration. What appears to be missing can always guide us to a healthier form.
But we can only do this if we have the properties for our domain. These properties are unknown with code and, like with prose, possibly absent. However, the payoff for discovering them could be huge.