According to C.K Allen, the sources of law are “the agencies through which the rules of conduct acquire the character of law by becoming definite, uniform and compulsory”.
Oppenheim also defines source of law as "the name for a historical fact out of which the rules of conduct came into existence and acquire legal force".
Merriam Webster defines a source of law as “something (as a constitution, treaty, custom, or statute) that provides the authority for judicial decisions and for legislation”.
Summarizing these definitions, a source of law can be understood as an authority from which laws obtain their legitimacy, validity, or force. This authority can be a formal source such as the constitution, can be legal sources such as legislation by the legislature arm of government and the decisions of judges (thus judicial precedent), can be material sources, and can be historical sources. These sources shall now be discussed.
1. The constitution:
The constitution is usually considered the most important source of law and its laws take precedence over the the laws of other sources of law. In Ghana for instance, the constitution in article 1(2) is said to be the supreme law and deprives any other law of validity if such law contravenes any provision of the constitution. When comparing the constitution to other essential sources of law such as the legislature, it is held that the constitution remains supreme. In the case of New Patriotic Party v. Attorney General for instance, Justice Aikins stated “In my view, even though Parliament has the right to legislate, this right is not without limitation.”
The enactments made by a country’s legislative arm of government is considered a source of law (or even law itself, making the legislature a source of law). This source of law is usually considered essential because it can amend or repeal existing statutes, replace various equitable principles and doctrines amongst others. De Lolme in highlighting the powers of the legislature particularly with regards to law-creation, is reputed to have said that "parliament can do everything but make a woman a man and a man a woman". Notice, however, that parliament in making legislature must not contravene the provisions of the constitution.
3. Common Law:
The common law, also known as case law, is regarded as an important historical source of English law. The common law is the body of laws obtained from judicial precedent, also known as stare decisis, rather than statues. Thus, decisions of previous judicial courts become an authority for subsequent judicial decisions. When courts do not want to stand by previous decisions, they must establish that the facts of the current case before them is materially different from the facts of the previous case in which the precedent was established. Another way a court can decide to not stand by precedence is to hold that the case in which the principle was established was decided per incuriam (thus was characterized by lack of due regard to the law or the facts). See the case of Duke v Reliance Systems Ltd.
In the 17th and 18th century, equity developed as an important source of law. It complemented the common law in areas it fell short. Equity usually refers to a set of remedies designed to promote natural justice. For instance, the equitable doctrine of promissory estoppel prevents a party from reneging on his or her promise when that promise was relied upon by another party to their detriment. Equity is expressly identified as a source of law in Ghana in article 11(2)
Customs are laws that are peculiar to certain communities and does not universally apply to all parties or bodies in a country. According to Ollenu & Woodman, customary law refers to “rules of law which by custom are applicable to particular communities…”. It is usually up to the courts to determine if a particular custom qualities as customary law. To make this decision, the courts may consult reported case, textbooks, and other appropriate authorities such as the authorities of the community in which a party claims such customary law exists. There is a common test known as the Blackstone test which must be proven by a person who alleges a customary right: The party must prove that the custom existed from time immemorial, was established by common consent and not through coercion or imposition, has an obligatory force, is consistent with other customs, and is a reasonable custom.
6. Canon Law:
This is considered the law of the catholic church and has had substantive influence on the growth of English law. Britannica defines Canon law as the body of laws made within certain Christian churches by lawful ecclesiastical authority for the government both of the whole church and parts thereof and of the behaviour and actions of individuals.