John Salmond, a legal scholar renowned for his ideologies on law in the field of jurisprudence, classified the sources of law into mainly two categories,i.e., material sources and formal sources.

Material sources

Material sources of law are those sources from which the law gets its content or matter, but not its validity. There are two types of material sources which are legal sources and historical sources. 

Legal sources 

Legal sources are the instruments used by the state which create legal rules. They are authoritative in nature and followed by courts of law. These are the sources or instruments that permit newer legal principles to be created. According to Salmond, legal sources of English law can be further classified into four categories- 

• Legislation, 
• Precedent, 
• Customary law, and
• Conventional law. 

Historical sources

Historical sources are sources that influence the development of law without giving effect to its validity or authority. These sources influence legal rules indirectly. The difference between legal and historical sources is that all laws have a historical source but they may or may not have a legal source. Decisions given by foreign courts serve as an example for this kind of source.