Philosophy of law is a branch of philosophy that examines the nature of law and law's relationship to other systems of norms, especially ethics and political philosophy. It asks questions like "What is law?", "What are the criteria for legal validity?", and "What is the relationship between law and morality?" Philosophy of law and jurisprudence are often used interchangeably, though jurisprudence sometimes encompasses forms of reasoning that fit into economics or sociology.
 Philosophy of law can be sub-divided into analytical jurisprudence, and normative jurisprudence. Analytical jurisprudence aims to define what law is and what it is not by identifying law's essential features. Normative jurisprudence investigates both the non-legal norms that shape law and the legal norms that are generated by law and guide human action.
 Unlike experimental jurisprudence, which investigates the content of legal concepts using the methods of social science, analytical jurisprudence seeks to provide a general account of the nature of law through the tools of conceptual analysis. The account is general in the sense of targeting universal features of law that hold at all times and places. Whereas lawyers are interested in what the law is on a specific issue in a specific jurisdiction, philosophers of law are interested in identifying the features of law shared across cultures, times, and places. Taken together, these foundational features of law offer the kind of universal definition philosophers are  after. The general approach allows philosophers to ask questions about, for example, what separates law from morality, politics, or practical reason. Often, scholars in the field presume that law has a unique set of features that separate it from other phenomena, though not all share the presumption.
 While the field has traditionally focused on giving an account of law's nature, some scholars have begun to examine the nature of domains within law, e.g. tort law, contract law, or criminal law. These scholars focus on what makes certain domains of law distinctive and how one domain differs from another. A particularly fecund area of research has been the distinction between tort law and criminal law, which more generally bears on the difference between civil and criminal law.
 Several schools of thought have developed around the nature of law, the most influential of which are:
 In recent years, debates about the nature of law have become increasingly fine-grained. One important debate exists within legal positivism about the separability of law and morality. Exclusive legal positivists claim that the legal validity of a norm never depends on its moral correctness. Inclusive legal positivists claim that moral considerations may determine the legal validity of a norm, but that it is not necessary that this is the case. Positivism began as an inclusivist theory; but influential exclusive legal positivists, including Joseph Raz, John Gardner, and Leslie Green, later rejected the idea.
 A second important debate, often called the "Hart–Dworkin debate", concerns the battle between the two most dominant schools in the late 20th and early 21st century, legal interpretivism and legal positivism.
 In addition to analytic jurisprudence, legal philosophy is also concerned with normative theories of law.  "Normative jurisprudence involves normative, evaluative, and otherwise prescriptive questions about the law." For example, What is the goal or purpose of law?  What moral or political theories provide a foundation for the law?  Three approaches have been influential in contemporary moral and political philosophy, and these approaches are reflected in normative theories of law:[citation needed]
 There are many other normative approaches to the philosophy of law, including critical legal studies and libertarian theories of law.
 Philosophers of law are also concerned with a variety of philosophical problems that arise in particular legal subjects, such as constitutional law, Contract law, Criminal law, and Tort law. Thus, philosophy of law addresses such diverse topics as theories of contract law, theories of criminal punishment, theories of tort liability, and the question of whether judicial review is justified.