In our book The Elephant in the Brain, Hidden Motives in Everyday Life, Kevin Simler and I first review the reasons to expect humans to often have hidden motives, and then we describe our main hidden motives in each of ten areas of life. In each area, we start with the usual claimed motive, identify puzzles that don’t fit well with that story, and then describe another plausible motive that fits better.

We hoped to inspire others to apply our method to more areas of life, but we have so far largely failed there. So its past time for me to take up that task. And as law & economics is the class I teach most often, that’s a natural first place to start. So what are our motives regarding our official systems for dispute resolution?

Saying the word “justice” doesn’t help much; what does that mean? But the field of law and economics has a standard answer that looks reasonable: economic efficiency. Which in law translates to encouraging cost-benefit-optimal levels of commitment, reliance, care, and activity. And the substantial success of law and economics scholarship suggests that this is in fact an important motive in law. Furthermore, as most everyone can get behind it, this is plausibly our most overt motive regarding law. But we also see many puzzles in law not well explained by this approach. Which suggests to me three other motives.

Back in the forager era, before formal law, disputes were resolved by mobs. That is, the local band talked informally about accusations of norm violations, came to a consensus about what to do, and then implemented that themselves. As this mob justice system has many known failure modes, we probably added law as a partial replacement in order to cut such failures. Thus a plausible secondary motive in law is to try to minimize the common failings of mob justice, and to insulate the legal system from mob influence.

The main failure of mob justice is plausibly a rush to judgment; each person in a gossip network has local incentives to accept the stance of whomever first reports an accusation to them. And the most interested parties are far more likely than average to be the first source of the first report someone hears. In response, law seeks to make legal decision makers independent and disconnected from the disputants and their gossip network, and to make such decision markers listen to all the evidence before making their decision. The rule against hearsay evidence is also plausibly to limit the influence of gossip on trials.

Leaders of the legal system often express concerns about its perceived legitimacy, and this makes sense as a third motive of the legal system. And as the most common threat to such legitimacy is widespread criticism of particular legal decisions, many features of law can be understood as ways to avoid such criticism. For example, criticism is likely cut via having legal personnel, venues, and demeanors be maximally prestigious and deferential to legal authorities.

Also, the more complex are legal language and arguments, the harder it becomes for mobs to question them. The longer the delay before final legal decisions, the less passion will remain to challenge them. Finally, the more expensive is the legal process, the fewer rulings there will be to question. Our most official legal systems differ from all our other less official dispute resolutions systems in all of these ways. They are slower, more expensive, less understandable, and more prestigious.

The last hidden motive that I think I see is that each legal jurisdiction wants to look good to outsiders. So most every jurisdiction has laws against widely disapproved behaviors, such as adultery, prostitution, or drinking alcohol on the street, even though such laws are often quite weakly enforced. Most set high standards of proof and adopt the usual rules constraining what evidence can be presented at trial, even though there’s little evidence that these rules help on net.

Most jurisdictions pretend to enforce all laws equally on everyone, but actually give police differential priorities; some locations, suspects, and victims count a lot more than others. It would be quite feasible, and probably lot more efficient, to use a bounty hunting system to enforce laws, and most locals are well aware of these varying priorities. But that would require admitting such differential priorities to outsiders, via explicit differences in the bounties paid. So most jurisdictions prefer government employees, who can be more hypocritical.

Similarly, our usual form of criminal punishment, nice jail, is less efficient than all the other forms, including mean jail, exile, corporal punishment, and fines. Holding constant how averse a convict is to suffer each punishment, nice jail costs the most. Alas, the world has fallen into an equilibrium where any jurisdiction that allows any punishment other than nice jail is declared to be cruel and unjust. Even giving the convict the choice between such punishments is called unjust. So the strong desire to avoid such accusations pushes most jurisdictions into using the least efficient form of punishment.

In sum, I see four big motives in law: encouraging commitment and care, avoiding failings of mob justice, preserving system legitimacy via avoiding clear decisions, and hindering distant observers from accusing a jurisdiction of injustice, even if most locals are not fooled.

One can of course postulate many more possible motives, including diverting revenue and status to legal authorities, preserving and increasing existing inequalities, giving civil authorities more arbitrary powers, and empowering busybodies to meddle in the lives of others. But it isn’t clear to me that these add much more explanatory power, given the above motives.