A legal custom is the established pattern of behaviour which will be objectively verified within a specific social setting. A claim is often administered in defence of "what has always been done and accepted by law". Related is that the idea of prescription; a right enjoyed through long custom instead of positive law. Most customary laws affect standards of community that are long-established during a given locale. However, the term also can apply to areas of the law of nations where certain standards are nearly universal in their acceptance as correct bases of action – for instance, laws against piracy or slavery (see hostishumani generis). In many, though not all instances, customary laws will have supportive court rulings and case law that has evolved to offer additional weight to their rule as law and also to demonstrate the trajectory of evolution (if any) within the interpretation of such law by relevant courts. Nature, definition and sources

In Hart's analysis, then, social rules amount to the custom that has legal force. Hart identifies three other differences between habits and binding social rules. First, a social rule exists where society frowns on deviation from the habit and attempts to stop departures by criticizing such behaviour. Second, when this criticism is seen socially as a legitimate reason for adhering to the habit, and it's welcomed. And, third, when members of a gaggle behave during a common way not only out of habit or because everyone else is doing it, but because it's seen to be a standard that ought to be followed, a minimum of by some members. Hund, however, acknowledges the problem of an outsider knowing the size of those criteria that depend upon an indoor point of view.


The term custom and usage is usually utilized in mercantile law, but "custom" and "usage" are often distinguished. Usage may be a repetition of acts whereas custom is that the law or general rule that arises from such repetition. A usage may exist without a custom, but custom cannot arise without a usage accompanying it or preceding it. Usage derives its authority from the permission of the parties to a transaction and applies only to consensual arrangements. A custom derives its authority from its adoption into the law and is binding no matter any acts of consent by the parties. In modern law, however, the two principles are often merged into one by the courts.