Final answer:
Studying legal principles and cases is best described as 'arguing', which involves reasoning and discussing interpretations of the law.
Step-by-step explanation:
When studying legal principles and cases, the action of interpreting and analyzing these principles is best described as arguing. Arguing, in this context, refers to the reasoned process of discussing the merits of different interpretations of the law based on precedents and legal theory. It is a foundational method used by lawyers, judges, and students to understand the application of legal concepts and to develop legal arguments.