Students sometimes misunderstand or misinterpret scientific content because of persistent misconceptions that need to be overcome by science education--a learning process typically called conceptual change. The acquisition of scientific content matter thus requires a transformation of the initial knowledge-state of a common-sense picture of the world to an outcome state of a scientific conception articulated with scientific concepts, which the learner did not possess prior to learning. This paper introduces a taxonomy based on the idea that multiple operational criteria are needed to evaluate conceptual change into scientific concepts. Three sets of criteria--qualitative, quantitative and experimental--are identified, and their interrelations in the process of conceptual change are explored.