Plucknett contrasts the flexibility and adaptability of customary law with the rigidity and remoteness of state legislation (1956)
In his history of the English common law Theodore Plucknett (1897-1965) stresses how flexible and adaptable customary law was in the middle ages. Unlike modern legislation created by the state, medieval communities were constantly changing their “customs” to suit their changing needs:
The middle ages seem to show us bodies of custom of every description, developing and adapting themselves to constantly changing conditions. We can see the first beginnings of a custom and trace its rise and modification; we can even see it deliberately imported from one place to another; it is a common sight to see a group of townspeople examine the customs of more advanced communities, choose the one they like best, and adopt it en bloc as their own. Indeed nothing is more evident than that custom in the middle ages could be made and changed, bought and sold, developing rapidly because it proceeded from the people, expressed their legal thought, and regulated their civil, commercial and family life. The custom of a mediaeval community may well have been much more intimately a product of the work and thought of those who lived by it, than is a modern statute enacted by a legislature whose contact with the public at large is only occasional.
The Harvard and LSE legal historian Plucknett delves deep into the English past in order to provide us with a massive survey of the evolution of English common law. What is not well appreciated is how flexible customary law was in the middle ages. The phrase “immemorial custom” suggests that custom, once it was accepted, was fixed for all time. Plucknett argues that this was not the case, that in fact, medieval customary law was flexible and changed quite quickly as it was adapted to the ever changing needs of the communities it served. He quotes the 13th century French maxim that “twice makes a custom.” A point he does not develop at length but which is taken up in detail by E.L. Jones is the idea of “the spread of best practice” as communities borrow legal rules and practices that seem to work well in other communities and adapt them for their own purposes. The chapter ends with a useful discussion of one of the best developed branches of medieval customary law, the law merchant, where the spread of best legal practice turned “what used to be the custom of numerous towns and fairs became the unified custom of a particular class, that of the merchants.” All of this happened without the need for any central control or direction by any state institution.