A few examples can be given to illustrate what the term ‘sources of law’ means in the legal context:
Multilateral international conventions are a source of law for states that ratify them that can become part of the positive law of the domestic legal order in various ways, depending on whether the state in question is has a monist or dualist system.
- E.g. The Vienna Convention on Road Traffic sets out i.a. the requirements that must be met when driving outside the country of registration. It includes a binding obligation for states to recognize the legality of vehicles from signatory countries.
Case law is a binding source of law, and a large number of states also adhere to a rule of binding precedent or ‘stare decisis’.
- E.g. Someone is apprehended on an outstanding warrant for driving with a suspended license. After the arrest has already been made, the police search the vehicle without a warrant and find drugs. The case is brought to court, which rules that because this search had been conducted without a warrant it violated the Fourth Amendment’s prohibition of unreasonable searches and seizures. This decision is binding as a source of law and sets a rule of precedent that needs to be followed in principle in consequent cases.
- In coming to the decision whether or not this is a violation of the Fourth Amendment the court must make use in their legal interpretation and reasoning of a fundamental principle of ‘reasonableness’ as source of law in coming to their conclusion.