Most moderns take it for granted that law is, must be, enforced by the state. Criminal offenders are detected and arrested by police, prosecuted by government prosectors, tried in government courts and punished by the government. Eighteenth century England provides a modified version of that system, with criminals, like tortfeasors in a modern system, detected and prosecuted privately but tried and punished by the state.
We have, however, looked at a number of societies in which law enforcement is or was private and decentralized. That pattern, although strange to us, is historically common. It seems likely that in many, perhaps most, societies, it was the original form of law on top of which later legal systems were constructed.
I call it feud law. Its logic is simple. If you wrong me, I threaten to harm you unless you compensate me. In order to work, it must solve four different problems:
1. My threat to harm you must be more believable if you have wronged me than if you have not.
2. There must be ways of making it likely that I will carry out my threat despite the risks.
3. There must be ways of enforcing the rights not only of the strong but of the weak.
4. There must be ways of terminating feud, preventing the pattern of continued back and forth violence that the word suggests to the modern ear.
All of these problems must be solved for feud to provide an adequate mechanism to enforce law. All of them have been solved in real world feud systems.
1. Right Makes Might
If my threat is equally effective whether or not you have actually wronged me, it works as well for extortion as for law enforcement. A feud system requires some mechanism that makes the threat more believable when you have wronged me than when you have not.
For one way of solving this problem, consider the case of saga period Iceland. If I believe you have wronged me, I take you to court. The court gives a verdict—you owe me fifty ounces of silver. You pay or you do not pay. If you do not pay, the court outlaws you. Once you are outlawed, it is legal for me to kill you, illegal for anyone to feed you, shelter you, defend you. Friends who might want to defend you know that any clash will lead to further legal suits in which they will be on the losing side. If they refuse to pay damages, the kin of anyone they injure will be pulled into the coalition against them. The court system is the mechanism through which right, as defined by the existing law code, makes might.The Romanichal achieve the same objective in a less formal way. Instead of a law code there is a system of community norms. If you have wronged me as judged by those norms and fail to compensate me, my friends will back me in the resulting clash, your friends will not back you.
The legal system of Somaliland is somewhere between the two. Law is customary—unlike the Icelandic case, there is no legislature. The courts that settle disputes are ad hoc, formed for the dispute. But they have enough legitimacy, in the eyes of neighbors and potential allies of both sides, to give their verdict weight.
The details vary from one system to another but the basic logic is the same.
When I threaten to harm you, you respond that if I do you will retaliate, making the exchange a loss for both of us. For the system to work, I need some way of committing myself, some way of making it in my interest to carry out my threat despite the risk, in your interest to back down and compensate me.
The simplest solution to this problem predates our species–territorial behavior in animals. One member of a territorial species somehow marks the territory he is claiming. Doing so turns a metaphorical switch in his brain, commits him to fight more and more desperately against a trespasser the further into the territory the trespasser comes. Unless the aggressor is much stronger than the defender a fight to the death is a loss for both. So once the commitment is clear, it is in the interest of the trespasser to retreat.
The corresponding mechanism in humans, used to defend a much broader set of claims, is vengefulness. When someone has wronged you, you very much want to get back at him, even at some risk. Considered ex post, after the fact, it looks like an irrational passion, one that can quite easily get you killed. Considered ex ante, it may well be a rational commitment strategy. The fact that you will revenge yourself against anyone who wrongs you, even at considerable cost to yourself, is a reason not to wrong you.
Human societies provide other commitment strategies as well, most obviously reputation and status. Your failure to carry through on your threat, to revenge yourself on one who has wronged you and refused to pay compensation, marks you as a wimp. Being known to be a wimp lowers your status in most human societies. It also marks you as an easy target for future wrongs.
Failing to revenge wrongs costs status. Forcing the person responsible for a wrong to pay compensation gains status, even if the wrong was to someone else. That explains the volunteer enforcer, someone who faces down an aggressor on behalf of a victim too weak to do it himself, a pattern we observe in the Icelandic sagas and in accounts of conflicts among the Commanche indians.
What if the wrong you suffer leaves you dead, unable to either threaten or execute vengeance? To deter killing, you need a commitment strategy that lasts past death. Real world feud systems provide it.
Under Icelandic law, killing me gives my kin a claim against you, the right to collect money damages and, if not suitably compensated in an out of court settlement, have you outlawed. The kin have a double incentive to enforce that claim. It may let them collect a considerable amount of money. It also gives anyone else who might want to kill one of them a reason not to. The same mechanism, a claim for damages inherited by the living, exists in other feud systems, such as the Somali.
3. Protecting the Weak
A fight to the death between two birds may be a loss for both, but a fight to the death between an elderly man with no allies and an aggressor backed by half a dozen friends is likely to be a loss for only one. In order for feud to do an adequate job of protecting rights, it needs some mechanism that works for weak as well as for strong.
The Icelanders solved that problem by making claims for damages transferable. The elderly man who knows that if he tries to prosecute his claim himself he is likely to be beaten up on his way to the court transfers his claim to a friend or neighbor who can enforce it. If enforcing it is not too hard, they split the cash. And however the compensation is divided, at least the aggressor has paid for his crime.
The Somali had a different system. The individual is a member of a diya-paying group, a coalition formed in advance. If he is wronged, the other members of the group are entitled to part of the damages—and have an incentive to make sure they are paid.
4. Terminating Feud
The simplest way of ending a feud is for one side to compensate the other for the damage done, ideally at the first step. One reason not to is the belief by the initial aggressor that he can get away with refusing, that the other will back down. Another is the belief that he does not owe anything, that he is in the right. If he is in the right and pays anyway that will mark him as a wimp, an easy target. Better to respond to force with force and hope the other party will back down instead.
The Icelandic solution was arbitration. Find someone prominent, respected, powerful. Have both parties agree to accept his settlement of the dispute. Paying what he says you owe does not mark you as a wimp. Refusing to do so not only makes you look bad and makes settlement more difficult in any future dispute, it gets you a new and powerful enemy. A similar approach was used by at least some other feud societies.
The Somali case also demonstrates a broader solution. When the amount of killing reaches an unacceptable level, raise the price–have both of the clans whose members have been feuding agree to increase wergeld for future settlements.
The First Legal System
No modern state uses a feud system to settle conflicts among its citizens, although some groups within modern states, such as the Romanichal or Kale, continue to do so. But a number of existing legal systems show clear evidence of having been built on top of pre-existing feud systems.
The clearest example is Anglo-American common law. It evolved out of Anglo-Saxon law. Anglo Saxon law, at least prior to its final century, was essentially Icelandic law plus a king. The king claimed that some offenses were violations of the king’s peace, hence that offenders owed damages to both him and the victim. Expand that approach enough and eventually the exception swallows the rule, converting all crimes into offenses against the crown.
For another example, consider Jewish law, possibly the best documented legal system we know of. The rules for killing, described in Chapter XXX, put the job of executing a killer whose crime is ruled capital on the Avenger of Blood, the heir of the victim. They also give him the right to kill a killer whose crime is ruled not capital if he can intercept him on the way back to his city of refuge. Similarly, Islamic law assigns the job of prosecuting a killer to the victim’s kin, gives them the right to retaliation if the killing was capital and of collecting diya, wergeld, from a non-capital killer or a capital killer against whom they choose not to retaliate.
Roman law, on which European civil law is ultimately based, is a more complicated case. Its earliest known form, the Law of the Twelve Tables, has survived only in fragments deduced from other documents. It has features that suggest a pre-existing feud system, such as references to the circumstances under which a victim is entitled to kill someone who has committed a crime against him. Later Roman law preserves extensive elements of private action, obligating the plaintiff to bring the defendant to court, if necessary by force, and giving a successful plaintiff in some contexts the right to kill the defendant or sell him into slavery. Theft in early Roman law was treated as a tort, only later also as a crime. 
Feud in the Modern World
Modern legal systems are based on centralized enforcement by the state but behavior within them can sometimes be understood by the logic of feud law. The enforcement of private norms of behavior, for example, is done by private action, at least some of which involves the threat of retaliation—true hostile gossip and sometimes more. Robert Ellickson, in his description of the system of norms of neighborly behavior in modern day Shasta County, California, gives an example. If a neighbor who lets his cattle stray into another’s field and damage his crop fails to apologize and help undo the damage, the victim may respond by driving the cattle off his property and a fair distance down the road in the direction away from their owner’s farm.
Another example is patent litigation among high-tech companies. Imagine that Apple is considering suing Samsung for a patent violation of which it does not believe Samsung is actually guilty—the equivalent, in the modern context, of a Romanichal Gypsy or medieval Icelander wronging someone by attacking him for no good reason. There are at least two reasons why Apple might do so. One is the chance that the court will mistakenly decide in Apple’s favor, patent law being a complicated subject. The other is that the litigation imposes significant costs on a rival. The public perception that Samsung might have to withdraw products from the market or modify them will cost Samsung sales, some of which will go to Apple.
One argument against suing, however, is the risk that Samsung might retaliate. Even if neither company has actually violated the patents of the other, the countersuit may still be profitable for the same reason as the initial suit. And even if the countersuit is not profitable as a gamble on court error or a way of reducing Apple’s sales in favor of Samsung’s, being committed to such a countersuit is one way of deterring the initial suit, just as being committed to vengeance against anyone who kills your kin is one way of keeping your kin from getting killed. The implicit feud system in modern patent litigation provides a mechanism for deterring meritless suits that might otherwise be profitable just as explicit feud systems deter other forms of otherwise profitable wrongs.
What about suits that are not meritless—what if Samsung actually has infringed Apple’s patents? The threat of countersuit is still a cost to Apple of suing. If courts reached their verdicts at random, the situation would be the same as in the meritless case and the feud system would equally deter suits in both cases.
But courts do not reach their decisions at random. If Samsung is guilty, that raises, one hopes substantially, the chance that Apple will win, increasing the benefit to Apple of suing. If Apple has not infringed Samsung’s patents, that reduces the benefit to Samsung of countersuing. The mechanism through which right makes might in the high tech feud, as in Iceland a thousand years ago, is the court system.
As long as the plaintiff is more likely to prevail when he is in the right than when he is in the wrong, suing someone for infringing your patents produces a larger benefit to the plaintiff and a larger cost to the defendant when the defendant actually has infringed the plaintiff’s patents than when he has not. Provided that the cost imposed by the threat of countersuit is greater than the benefit of a meritless suit but less than the benefit of a legitimate suit, the result is to deter the former but not the latter.
The clearest anecdotal evidence that what I have described is how the system actually works is the practice of high-tech companies accumulating large inventories of patents, many of which they are unlikely to use. It is the modern equivalent of the medieval Icelander accumulating weapons and allies in case he ever needs them to prosecute his side of a feud. As in that case–and the somewhat higher stakes version played by nations under the name of Mutual Assured Destruction–if the strategy works the weapons need never be used.
There remains, however, one hole in the system.
The Invulnerable Plaintiff
Samsung and Apple both produce cell phones, making both vulnerable to threats of retaliation. A firm that produces nothing is not. A non-practicing-entity, referred to by critics as a patent troll, owns a collection of patents, practices none of them, sues practicing entities for alleged infringement but faces no risk of an infringement countersuit. It is invulnerable to retaliation.
The non-practicing entity, like Apple, has the possibility of profiting by court error, of winning a case it should have lost and collecting damages. And although imposing costs on Samsung provides no direct benefit to the non-practicing-entity, it does give Samsung an additional incentive to settle instead of letting the case go to trial.
In the case of Samsung, there is an obvious incentive not to settle—paying off one plaintiff with a weak case will encourage others. That incentive is weaker in the case of a much smaller firm, unlikely to be the target of multiple extortion attempts and at risk of being destroyed by a single law suit. Hence we get what critics of non-practicing-entities allege to be their usual tactic—suing small firms in order to be paid to drop the suit.
It follows that, even if the feud system is adequate as a way of controlling patent suits among producing companies, it is impotent to control bogus patent suits by non-practicing entities. Which suggests that we may need something else. For one possible solution, see Chapter XXX [ideas for us].
Ellickson, Robert, Order Without Law, Harvard University Press1994.
Friedman, David, "A Positive Account of Property Rights," Social Philosophy and Policy 11 No. 2 (Summer 1994) pp. 1-16.
Friedman, David, The Machinery of Freedom: Guide to a Radical Capitalism, 2014.
 Describing it as private raises the question of how one distinguishes between a government and private institutions to enforce rights, commonly regarded as a governmental function. For my answer to that question see Friedman 2014, Chapter 52.
 The feud systems we have looked at are saga period Iceland, northern Somalia, Commanche Indians, the Romanichal and Kale Romani. Other feud systems I am aware of include the Bedouin system described in a paper by one of my students, webbed at http://www.daviddfriedman.com/Academic/Course_Pages/
Legal_Systems_Very_Different_13/LegalSysPapers2Discuss13/Bedouin_Law.htm and the northern Albanian system described in The Code of LekĎ Dukagjini.
 I am describing a feud system not a feudal system. The two words sound similar but are unrelated in both meaning and etymology. “Feudal” comes from medieval Latin “feodum,” meaning a fief or fee, from Frankish fehu (cattle, owndom, property, fee) possibly from proto-germanic “fehu” (cattle) from Indo-European *peḱu-, livestock. “Feud” comes from “fede” (“enmity, hatred, hostility”) ultimately from proto indo-European root *peig- “evil minded, hostile.”
 For a good webbed discussion, see http://people.eku.edu/ritchisong/birdterritories.html. Possibly Alcock, John. Animal Behavior: An Evolutionary Approach, Tenth Edition. Massachusetts: Sinauer Associates, Inc., 2013
 I discuss rights among humans, considered not as a moral or legal category but a description of behavior, as a more elaborate version of the same pattern of behavior in Friedman 1994 and Friedman 2014, Chapter 52.
 Cite my chapter.
 Ellickson 1994.
 Insert a cite to a news story on this.