This chapter focuses on how designers solve problems in the conceptual design phase; a phase in which information-processing and decision-making are very intensive as a consequence of generating and evaluating alternative ideas. The aim is to demonstrate an epistemological and methodological approach that permits researchers to capture, describe, prioritize, act on, and evaluate alternative design solutions. Thus, the main emphasis of the chapter is to provide a framework for understanding how methods and knowledge are linked within the cognitive strategies of design when creating interiors. The framework is discussed through a focus on aging adults. This population is selected as the focus because of the complexity of issues that confront designers when creating interior spaces for maturing populations. In the design of interior environments for maturing populations it may be necessary to apply variations of each of the priority-setting techniques.