This article aims to make clear the benefits the multicriteria-method gives to scientific assessment which are consistent with a rationality framework. It begins by referring to the scientific method, through which humankind tries to understand the world building an artificial world from science. Afterwards a reflection on the added value qualitative methods as a methodology can give, is presented since they allow a broader worldview by taking into account variables that cannot be expressed quantitatively. Finally, a multicriteria-method is presented as a useful tool to determine the impact of actions on sustainability, while incorporating the existing conflicts between economic, environmental and social objectives, and between different levels of decision making in scientific assessment.