The goal of design is to change the built environment. The designer is the actor in this process initiating changes of the existing world situation to a new world situation. He is also a member of the design coalition team. Arguably the keyword in this process is 'change', caused by a chain of design decisions made in the context of a dynamic model of the design activity, based on the design-knowledge.
The latter are arguably, in most cases, overt expressions of the physical world including interpretations, abstractions, formalisms, etc. Design knowledge can improve the quality of design decisions, being generated by the design activities. However, the goal of design is not to produce knowledge, but rather to take actions to change the built environment. The main question is not a design decision support system that is partially or totally dependent on an organized body of design knowledge and means for their retrieval. Design decisions are largely influenced by experience, creativity, innovation and other factors. It is not always possible to utilize these factors in a formalized knowledge base. This paper discusses 'uncertainty' as one of the major factors influencing design decisions. It is not possible to eliminate uncertainty in design processes but rather we have to minimize the influence of uncertainty on design decisions and aim at increasing the quality of design decisions.