The difference between inventive problems and optimization ones is defined in this article. There exist among the engineering practices different kind of tools and methods aiming at designing, but which are not specified for the same nature of problem. It is thus relevant to be able to recognize the two kinds of problems: optimization ones, for which a solution can be found by adjustment of the value of problem parameters; and inventive problems, for which no solution is known. If no solution is known, either a solution exists and has to be found, it means that it has not been formulated the right way; either no solution exists and it is required to use a method to invent a solution. For these two cases, the matter is the problem, as it is modeled has to be reformulated, the model has to be changed, in order to build a representation enabling the resolution of the problem. The article will be focused on the question of problem model change and will compare the mechanisms to change this model for inventive problems from two problem solving theories: dialectical methods and models, on the one hand; and constraint satisfaction problem (CSP), on the other hand.