# Revisiting Problem-Solution Co-Evolution in the Context of Team Conceptual Design Activity
## 1 Introduction  
Ever since the 1960s, the design process has been dominantly prescribed within the context of the problem-solving paradigm. The initial efforts of the design methods movement [1] utilised linear and high-level depictions of the design process, the most common being the analysis-synthesis-evaluation (ASE) sequence as part of a general problem-solving cycle (see, e.g., [2; 3; 4] for the initial developments of ASE-based models). The work of [PERSON] [5] further strengthened the paradigm by laying down the scientific foundations of designing as a problem-solving activity [6; 7]. As such, the conventional \"analyse-synthesize-evaluate\" approach has been seen as a recurring and dominant model of design, used primarily in design education, but also as one that is reported to work well in design practice, especially in the engineering design domain [8]. A typical engineering design textbook (see, e.g., [9; 10]) will thus define designing as a process in which information in the form of requirements, constraints, and needs (the problem) are systematically being converted into information describing technical systems (the solution). The systematic approach prescribes designers with a simple and linear process that can be applied at various points of the engineering design process: To collect a sufficient amount of information, to confront the problemby formulating the objectives and main constraints, to create solution alternatives, to evaluate them, and, finally, to make a decision on the final solution [11; 12; 13; 14; 15]. Simply put, the systematic design implies gradual movement from the design problem to the design solution, as well as from analytic over synthetic towards evaluative processes. Hence, the prescriptive engineering design literature instructs designers to always start with the analysis of design requirements, constraints, and needs in order to apprehend the overall problem, before they can start synthesising and evaluating solution alternatives that address the problem. Nevertheless, the descriptive research streams (which have been focused on investigating how designers really work) revealed that this is not what designers tend to do when they come across new, unique, or ill-defined problems [16; 17] and that the reality of design projects is in no way a gradual movement from problem to solution, nor from analysis to evaluation [18; 19]. The descriptive approaches rather utilise a co-evolution perspective, where the design problem and solutions to the problem are developed in parallel, through a constant iteration of ASE [20]. According to the co-evolution perspective, new problem entities result from exploring possible design solutions, as well as the other way around [21; 22]. It hence proposes a separation of the design space into two notional spaces: the problem and solution space. The first constitutes from problem space entities, such as requirements, constraints, and needs, whereas the latter consists of solution space entities, such as solution ideas, concepts, working principles, etc. Designers explore both spaces and switch between them, and as a result, the spaces co-evolve. The switching in-between the spaces appears causal in nature, while activity in one space associates to the activity in the other space in a highly interactive manner [23; 24]. Due to its focus on the evolution of both the design problem and the design solutions, the co-evolution perspective has often been utilised to study design creativity [20; 21; 22; 23; 24]. Despite the different viewpoints on the nature of the design process, both the prescriptive (e.g., conventional problem-solving) and descriptive (e.g., problem-solution co-evolution) design research streams agree that the most intensive design space exploration is likely to appear within the conceptual design phase of product development.