Today system design methods seem to presuppose the system design process as problem solving, i.e. as repair of a malfunctioning reality. Another assumption underlying these methods is the irrationality of system designers practice. This paper challenges this, often naive, view of rationality underlying system design methods by searching for the hidden rationality of practice.

Twenty system designers were interviewed about their view on design skill, design methods, quality and the 'nature' of system design. The answers of the designers in many cases contradicts basic assumptions underlying many of today's design methods, especially assumptions about the nature and rationality of the design process.

One conclusion of the study is that a general understanding of the existing design practice is of crucial importance to all method development, at least if the purpose is to create methods that will be accepted and understood by practitioners.