Jurisprudence is the study of the origin, structure, application and enforcement of law. The term itself is etymologically Latin, combining the terms for "law" and "knowledge," making it an appropriate term to apply to the academic category, the "philosophy of law." There are many theories that attempt to explain the nature, parameters and the trends of law within established legal structures and originating prior to the formal foundation of a new legal system.
There are different motivations in analysis of the philosophy or point of law. One assumes law exists in order to be changed in that it ought to be reformed when meeting a new social need or demand so that it would be compliant with the unforeseen situation. Another more common understanding is the pursuit of social stability and order by finding the optimum formulae of laws that would govern people. Philosophers also approach the problems within law, or the quirks to be analyzed within law, by examining two different angles. One examines issues with the structure of law and the systems that adjudicate it. Some might theorize that there are inherent flaws that undermine the authority of a government or let contradictory laws exist simultaneously. Another angle, similar to what is mentioned above, considers that law might be unduly influenced by the society and politics around it, perhaps reinforcing it or undermining its credibility as a mainstay.
There are four major schools of law. Natural law assumes something akin to absolute truths and/or absolute mores that predict natural limits to the extent laws can be legislated. There is also an assumption law is rational and within grasp of human reason, making any law passed needing to fit within the context of comprehension. Legal Positivism does not predicate law on absolute morals and that law exists based on the realities that enforce it. Legal Realism would consider Legal Positivism to focus too much on theory and the letter of the law, while law is actually a reflection of what is practiced rather than legislated or decreed. If a law exists but it is not enforced, theoretically it would not be law. Critical Legal Studies have broadened the philosophical realm to advocate that all law should be seen as inherently flawed and probably contradictory with other laws, mores and customs, thus necessitating thorough examination.
The idea that there is a Natural Law is ancient and found in nearly every society. It tends to be paired with religious thoughts on divine infallibility or philosophical considerations of absolute truths. Names as major for their societies like Aristotle and Thomas Aquinas advocated some general outlines of a Natural Law. Aristotle is said to base most of his theory on the so-called Golden Rule, where people would treat each other in a manner they would deem appropriate and worthy of their own treatment. This also assumes there is a common stream of legal thinking that will exist no matter how arbitrarily other actors might decree and legislate new laws. Thomas Aquinas conflates the idea that there is a natural stream of restrictions with the concept of natural rights. He also considers there to be several orders of law, namely: eternal, natural, human and divine.
Thomas Hobbes, one of the founding philosophers of the European Enlightenment, considered law to have gained the consent of the governed. This idea can work in tandem with concepts in customary law but not necessarily. Hobbes illustrates what would later be dubbed Social Contract Theory in his treatise Leviathan, where he describes legitimate forms of government.
Concomitantly, there exist other doctrines of law stemming from religious orders that have maintained their codes even while losing state authority. Judaism and Islam are the most apparent and developed examples to Western scholars, both also having similar legal principles and structures. Most importantly, the right to govern and legislate in these systems is based on divine authority. Primary in both systems is the will of God, which is said to have been revealed over time through various transmitters. With this, any other laws or amendments would be either inferior or illegitimate. In Judaism, Rabbinical authorities subjugate laws passed by their bodies over the centuries to the foundational laws as described in the Torah. Additionally, while customs may take on the force of law, they are made subject to the parameters of the Rabbis, and foremost the Torah's original injunctions. In both Judaism and Islam there is a reliance on a chain of authority that gains its legitimacy by interpreting the precedent laws of the revealed traditions.
Additionally, there is a rapidly developing concept of international law, which many point to as indispensable in order to govern norms between nations. Presumably, laws of war and international treaties would be used to enforce the greater good, perhaps in the spirit of Natural Law. However, Anthony Carty in his book indicates the analysis of such is underdeveloped and incredibly subjective.