Substantial disagreement exists concerning how designers in many fields, whether amateur or professional, alone or in teams, produce designs. Dorst and Dijkhuis argued that “there are many ways of describing design processes” and discussed “two basic and fundamentally different ways”, both of which have several names. The prevailing view has been called “The Rational Model”, “Technical Problem Solving” and “The Reason-Centric Perspective”. The alternative view has been called “Reflection-in-Action”, “Evolutionary Design”, “co-evolution”, and “The Action-Centric Perspective”.
The Rational Model
The Rational Model was independently developed by Simon and Pahl and Beitz. It posits that:
designers attempt to optimize a design candidate for known constraints and objectives,
the design process is plan-driven,
the design process is understood in terms of a discrete sequence of stages.
The Rational Model is based on a rationalist philosophy and underlies the waterfall model, systems development life cycle, and much of the engineering design literature. According to the rationalist philosophy, design is informed by research and knowledge in a predictable and controlled manner. Technical rationality is at the center of the process.