Before we can define private law theory, we must define private law. Private law is made of two major component bodies of law - namely, property law (land, items in one's possession, intellectual property claims, etc.) and laws of obligation (contracts, torts, unjust enrichment, etc.). It does not include any form of criminal law. What constitutes a contract, rights on intellectual property and many other mentioned areas do vary across jurisdictions, making the study of private law theory localized geographically for the most part.
Now that we understand what we are looking at, we must clarify how and to what ends we mean to investigate private law; this is where the 'theory' comes in. In truth, private law theory is not so much a single unifying theory, although that is the ultimate aim of some private law scholars, but an umbrella term for theories revolving around many aspects of private law. Some focus on the merit of these laws - whether they are fair and just and compatible with the culture's morals - while other are more concerned with the performance of private law in general - how it is applied and perhaps circumnavigated in court and whether it succeeds in delivering justice in an efficient, comprehensive manner. A third area of private law theory is the comparative study of private law across jurisdictions in states, countries and even global agreements. This area draws on the other two aforementioned ones to observe what makes private law fair and effective in different cultures. In some cases, scholars of this sub-discipline are consulted in global legal agreements with the aim of improving or perhaps one day standardizing private law on a larger scale.
However one approaches this subject, a broad range of knowledge in and outside legal studies will be an advantage. Sociology, philosophy, anthropology, economics and more all have a part to play in this intricate field of study.
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