Notes on the Synthesis of Form

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A book by Christopher Alexander on the process of design.

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After characterizing the design process, Alexander proposes a design method based on the functional decomposition of a problem. Alexander argues that the design will be successful if the process and the structure of the form are isomorphic to this functional decomposition.

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The Design Process

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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.

Christopher Alexander, "Notes on the Synthesis of Form"

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The goal of the design process is to attain fitness between a form that we control and a context that we do not control. If we could give a formal description of the forces of the context, we would not have a design problem. What makes the problem difficult is that we don't fully understand the field of forces of the context. Understanding this field and making the form that fits it is really two aspects of the same problem.

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In practice the designer finds those forces through a negative process of identifying misfits. A misfit is a problem that occurs when we put the form in its context. As form and context changes, those misfits change and the form needs to adapt.

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Alexander represents a design problem as a system of misfits. The misfits that have a causal linkage will be connected. Because the misfits are not all strongly connected, subsystems will form. The design process can then be represented as the actions on those subsystems. Alexander argues that the design process will be successful if those subsystems can evolve independently.

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System of misfits with two subsystems.
System of misfits with two subsystems.

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The inner nature of the building process is what matters. If the process allows this adaptation to happen progressively subsystem by subsystem, the form will always fit the context. Otherwise the form will be arbitrary and sensitive to any change in the context.

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The design process of the unselfconscious (traditional) culture is characterized by a lack of explicit rules. The builders learn through imitation and correction. The process is shaped by two major forces. First, the force of tradition prevents people to change the way they build shelters unless they have a good reason. Second, people in the unselfconscious cultures fix their own homes with local materials. They do not have to wait for the designer.

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Those two forces, tradition and quick feedback, define a process that generates well-fitting forms. The quick feedback ensures that misfits are fixed as soon as they occur, preventing multiple subsystems to be changed at once. The force of tradition prevent the other minor changes to be made in the rest of the system.

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Such process does not require excessive creative abilities from the agents. People need only to fix misfits as they uncover them. Wrong fixes will not be repeated.

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The two major forces responsible for the generation of well-fitting forms in the unselfconscious process disappear in the selfconscious (modern) culture. People no longer build or fix their own home. And the force of tradition disappears. Change becomes fashionable. But this does not explain in itself why the selfconscious process cannot generate good form.

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Because of the complexity of the problem and the need for explicit communication, the selfconscious designers introduce concepts and categories to describe the problem and its solutions. However, most of the time those categories do not correspond to the causal structure of the problem.

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Structural mismatch
Structural mismatch

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Worse, the designers lose the ability to change them. Once codified the rules are taught and most designers cannot see beyond them. And the forces that can easily be made explicit gain more weight than the ones that can't. The designer does not see the fit or misfit of the problem but adherence or deviation from his conceptual dogmas.

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A Design Method

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Alexander proposes to replace the subjective and arbitrary pictures of the selfconscious design process by a formal picture that respects the natural structure of the problem.

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During analysis, the designer must identify the misfits that are most likely to occur when the form is in its context. Those misfits should be (1) of equal scope, (2) as independent as possible, and (3) as small in scope as possible.

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Because the form will ultimately live in the physical world, some misfits will not be completely independent. Those causal linkages give the problem its structure. The task of the designer is to identify a decomposition of this system of misfits that allows the subsystems to be solved independently. This decomposition should attempt to minimize as much as possible the information content between subsystems. The decomposition ends when all subsets contain only one misfit.

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This functional decomposition of the problem acts as a program that directs the design process. The realization of the program consists in building constructive diagrams for each subset of requirements, starting at the bottom. A diagram is constructive if it illuminates both, requirements and form. A constructive diagram is at the same time a functional description and a structural description of the form. Those diagrams are then assembled to build the final design. While the task of analysis is top-down, the task of synthesis of a solution is bottom-up.

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A program as a tree of misfits and its realization as a tree of constructive diagrams.
A program as a tree of misfits and its realization as a tree of constructive diagrams.

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Those constructive diagrams are what Christopher Alexander calls design patterns in his later works.

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