Educational Discourses on the nature of science(NOS) identify understanding of the role of scientific knowledge, especially the distinction between law and theory, as a crucial goal of instruction. However, the scientist community uses the terms such as law, theory, and principle without explicit definition so that the terms have no coherent meanings in their conventional language expression. The inconsistency between the norm and the reality could impose confusion on the teaching and learning. From the awareness of the problem, this study critically reviews the science education research papers and literatures on the philosophy of science which focus on the meaning of law, theory, or principle and the structure of scientific knowledge. From the examination of the science education researches, it is revealed that the disparity between the normative meanings of the law and theory by NOS researchers and actual usage of the terms is quite serious. From the review of the literatures of the philosophy of science, the necessity of the distintion of three categories: law, theory, and principle beyond the dichotomy between law and theory is brought up. By synthesizing the related literatures, we provide an outline of the characteristics of knowledges belonging to law, theory, and principle. Considering the conflict between the normative definition and the conventional language, it could be unnecessary to emphasize clear distinction on the terms as an instructional goal. Instead, the goal of instruction should focus on that there are three types of scientific knowledges of different functions and characteristics.