What the subtractive process requires, more than anything else, is a firm understanding of necessity. Knowledge of universal human needs and the archetypal forms that satisfy them is a prerequisite for the practice of good design. This knowledge is available to anyone willing to pay attention.
A vernacular architect who has come across a photo of a Kirghizian yurt and encountered a Japanese unitized bathroom and a termite mound while traveling does not set out to build a yurt with a unitized bathroom and termite inspired air conditioning just to show what he has learned. He retains the forms for a time when necessity demands their use.
Vernacular architects do not strive to produce novel designs for novelty’s sake. Necessity must be allowed to dictate form. The architect’s primary job is to get out of its way. It might seem that such a process would produce a monotonously limited variety of structures, but, in fact, there is infinite variation within the discipline. Vernacular architecture is as diverse as the climates and cultures that produce it. The buildings in a particular region may all look similar as they have all resulted from the same set of socionatural conditions, but within these boundaries, there is also plenty of room for variance. With the big problems of design already resolved by the common sense of their predecessors, vernacular architects are left free to focus on the specifics of the project at hand. Instead of reinventing the wheel, they are left to fine-tune the spokes.
