In an imperfect world, imperfect men have never lived in harmony; the consequences have been inevitable, regrettable and, often, productive of legal history. Even the neatest householder, the most peaceable citizen, is sometimes a bad neighbour. He chooses to fiddle when I choose to nap; he permits his dog to howl at midnight; he kindles his back-yard fire where its smoke will choke my back-yard guests. More serious, and more relevant in terms of legal consequences, he manufactures strange and noxious odours which he allows to escape from his premises or he throws waste material into the stream which wanders across his property on its way to my own land. Disregard for the convenience, well-being and property rights of others is not unique to the twentieth century; the under-lying problem of the bad neighbour was well enough known to the twelfth. Then, and long thereafter, one man's mill needed more water to grind efficiently and so he diverted the millstream with only passing regret, if that, for what the diversion might mean to his neighbour's mill downstream. His sheep escaped from pasture and so he raised a hedge across an entry, thereby forcing his neighbour's flock to find a new and less convenient path.

Response could always be immediate and forceful; self-help has the virtues of speed, simplicity and cheapness. But unless the creator of the offending mill or hedge was willing to accept his neighbour's response, what was originally an attempt at unilateral solution of a problem could well escalate into a quarrel culminating in violence out of proportion to the issue.