Christopher Alexander was an American architect whose theories on human-centered design influenced architecture, urban design, sociology, and software programming.

In 1977 he published A Pattern Language, describing how the creative process gives rise to common patterns that are different in detail but similar in shape and form.

Together, these patterns form a language that describes the context, the problem, and known solutions which are self-referential. When the language is known, solutions can be recombined and reused effortlessly.

Designers aspire to make good designs and avoid making bad ones. Because we are taught ‘beauty is in the eye of the beholder’, some consider assessing good from bad design a subjective exercise.

However, Alexander asserts good and bad design is not a matter of opinion but an objective truth to be realized, but difficult to articulate.

Good design is self-sustaining and bad design is self-destructive, much like health and sickness. Good design is described as Alive, Whole, Eternal, or Truthful whereas bad design describes the lack of these qualities.

Suppose you remember a town, building, or garden you’ve visited. In that case, you may find the memory of the environment pleasurable or displeasing because of the presence or absence of a Quality Without A Name, or QWAN for short. Any place or product is judged by the QWAN it possesses or does not, but how do Pattern Languages help create QWAN or good design?

Alexander describes 253 patterns for Towns, Buildings, and Construction that define a problem, and a solution, and references similar patterns that may be composed into new solutions. One context is pedestrians walking near or crossing roads.

Road Crossing — Cars can scare people away from walking near roads even if places that people have the legal right-of-way. Narrow the road where the pedestrian path is, raise the path, put in islanders between driving lanes, and add a canopy to keep the path visible to…