Breakin' the Law
Meet the New Law, Same as the Old Law
Because law was an expression of a people, the idea of new law was alien. You don't have new customs. If a man steals a cow, you don't come up with a new way to judge the crime; you ask what is the customary punishment for the theft of a cow.
For a long time, new laws were couched in terms of being only a return to law or a correction to previous mistakes. Kings sometimes swore that they would introduce no new laws, for new laws could only be alien to the body politic.
City Air
Here as elsewhere, the cities formed a major exception. They were always needing new laws, for they kept getting into matters that the rural nobility never encountered. Chief among these was mercantile law.
Merchants were always encountering new situations that not only were not covered by customary law but were new even to the townsmen themselves. Their concern was not so much how tradition had to say as it was what the present had to say.
Moreover, towns weren't individuals. In the countryside, law was deeply and intimately personal: the expression of the people and their lord. In the towns law was corporate, the expression of an abstraction: the town government as a representative of "the people." This meant that law had a fundamentally different character in the towns, and this character was both unprecedented and constantly shifting.
It should be no surprise, then, that towns had their own laws, to a greater or lesser degree, and that they were constantly at odds with both the rural nobility and the clergy over matters of law and jurisdiction.