The contemporary national legal systems are generally based on one of four basic systems: civil law, common law, statutory law, religious law or combinations of these. However, the legal system of each country is shaped by its unique history and so incorporates individual variations. The science that studies law at the level of legal systems is called comparative law.

Both civil (also known as Roman) and common law systems can be considered the most widespread in the world: civil law because it is the most widespread by landmass and by population overall, and common law because it is employed by the greatest number of people compared to any single civil law system.
List the basis of contemporary national legal systems from the passage. Display the results in comma separated format.
civil law, common law, statutory law, religious law, comparative law