You observe a stranger, in public, in possession of what is obviously stolen property of significant value. You might ignore it, but you also might call the police.
Unless it's a shopping cart. The value of a shopping cart is about a hundred dollars and any that you observe outside the grocery and associated parking lot are almost certainly stolen. Yet, in practice, you do not call the police. My guess is that practically nobody does—or that the police don't come, or that if they come they make no effort to arrest the thief. The basis for that guess is casual observation—if there were any significant chance that walking off with a shopping cart would get you arrested, tried, and jailed with a sentence suited to the value of the cart, very few people would do it.
It strikes me as an interesting example of the tension between laws and social norms—or perhaps between laws and the commitment strategies that, as I have argued elsewhere
, play a large role in enforcing legal rules. Part of the reason you do not react to the thief as a thief is that this particular form of theft is so common. Shopping carts are treated by thieves, by observers of theft, perhaps also by police, as not quite private property. The attitude is reinforced by the fact that they are designed to be treated as temporary public property within the store and its parking lot. The logic of our moral beliefs, like the logic of the law, implies no more right to walk off with a shopping cart than to walk off with a bicycle. But that is not how most of us feel, at least judging by our behavior.
One consequence of our ambivalent attitude is to make enforcement of the law by those most obviously affected, the stores whose carts get stolen, risky. Imagine that one such grocery chain made a point of getting the local police to arrest, try and jail people found with their carts. Stealing their carts might become less popular—but so would shopping at their stores. A good many customers, observing such a severe sanction for what they intuit as a mild trespass, might decide that they preferred to shop somewhere else. In practice, so far as I can tell, stores mostly deal with the problem in ways
that do not depend on invoking their legal rights—sending people around to find and return abandoned carts or trying to design cart and parking lot in ways that making walking off with a cart more difficult.