There have been many attempts to produce "a universally acceptable definition of law". In 1972, one source indicated that no such definition could be produced. Glanville Williams said that the meaning of the word "law" depends on the context in which that word is used. He said that, for example, "early customary law" and "municipal law" were contexts where the word "law" had two different and irreconcilable meanings. Thurman Arnold said that it is obvious that it is impossible to define the word "law" and that it is also equally obvious that the struggle to define that word should not ever be abandoned. It is possible to take the view that there is no need to define the word "law" (e.g. "let's forget about generalities and get down to cases").
All legal systems deal with the same basic issues, but jurisdictions categorise and identify its legal subjects in different ways. A common distinction is that between "public law" (a term related closely to the state, and including constitutional, administrative and criminal law), and "private law" (which covers contract, tort and property). In civil law systems, contract and tort fall under a general law of obligations, while trusts law is dealt with under statutory regimes or international conventions. International, constitutional and administrative law, criminal law, contract, tort, property law and trusts are regarded as the "traditional core subjects", although there are many further disciplines.
International law can refer to three things: public international law, private international law or conflict of laws and the law of supranational organisations.
Public international law concerns relationships between sovereign nations. The sources for public international law development are custom, practice and treaties between sovereign nations, such as the Geneva Conventions. Public international law can be formed by international organisations, such as the United Nations (which was established after the failure of the League of Nations to prevent the Second World War), the International Labour Organisation, the World Trade Organisation, or the International Monetary Fund. Public international law has a special status as law because there is no international police force, and courts (e.g. the International Court of Justice as the primary UN judicial organ) lack the capacity to penalise disobedience. However, a few bodies, such as the WTO, have effective systems of binding arbitration and dispute resolution backed up by trade sanctions.
Conflict of laws (or "private international law" in civil law countries) concerns which jurisdiction a legal dispute between private parties should be heard in and which jurisdiction's law should be applied. Today, businesses are increasingly capable of shifting capital and labour supply chains across borders, as well as trading with overseas businesses, making the question of which country has jurisdiction even more pressing. Increasing numbers of businesses opt for commercial arbitration under the New York Convention 1958.
European Union law is the first and, so far, only example of an internationally accepted legal system other than the UN and the World Trade Organisation. Given the trend of increasing global economic integration, many regional agreements—especially the Union of South American Nations—are on track to follow the same model. In the EU, sovereign nations have gathered their authority in a system of courts and political institutions. These institutions are allowed the ability to enforce legal norms both against or for member states and citizens in a manner which is not possible through public international law. As the European Court of Justice said in the 1960s, European Union law constitutes "a new legal order of international law" for the mutual social and economic benefit of the member states..