The article discusses the fundamental legal concepts and their application in judicial reasoning, focusing on the contrast between legal and non-legal conceptions, operative and evidential facts, and fundamental jural relations. It emphasizes the importance of precise terminology in legal thought and expression, highlighting the need to avoid ambiguous terms that can lead to confusion and misinterpretation. The article particularly addresses the concepts of rights in personam (paucital rights) and rights in rem (multital rights), explaining that rights in personam are unique or limited to specific individuals, while rights in rem are part of a larger class of similar rights affecting a broad group of people. The discussion includes examples and judicial opinions to illustrate the practical implications of these concepts, aiming to provide a clearer understanding for law students and practitioners.The article discusses the fundamental legal concepts and their application in judicial reasoning, focusing on the contrast between legal and non-legal conceptions, operative and evidential facts, and fundamental jural relations. It emphasizes the importance of precise terminology in legal thought and expression, highlighting the need to avoid ambiguous terms that can lead to confusion and misinterpretation. The article particularly addresses the concepts of rights in personam (paucital rights) and rights in rem (multital rights), explaining that rights in personam are unique or limited to specific individuals, while rights in rem are part of a larger class of similar rights affecting a broad group of people. The discussion includes examples and judicial opinions to illustrate the practical implications of these concepts, aiming to provide a clearer understanding for law students and practitioners.