Economists often say that the law should be written to promote efficient outcomes. That’s more ambiguous than it sounds.
Suppose I want to take an action that causes you harm; for example, I want to cut down a tree that you like looking at. How do we tell if that action is efficient?
Definition 1. The action is efficient if my willingness to pay exceeds your willingness to accept. For example, if I’m willing to pay $100 for the privilege of harvesting the tree, and if you’d accept less than $100 to part with it, then the tree-cutting is efficient.
Definition 2. The tree-cutting is efficient if it would occur in a world with no transactions costs (i.e. a world in which there are no impediments to bargaining).
In many circumstances, these definitions are equivalent, and economists often pretend they’re equivalent always — but sometimes they’re not.
Example 1. I want to punch you in the nose non-consensually. (The non-consensuality is a big part of my enjoyment.) I’d pay $100 to punch you in the nose, and you’d accept $50 to take the punch. By Definition 1, the punch is efficient. But the punch would be unlikely to occur in a world with no transactions costs, because it would require bargaining, hence consensuality on your part, which kills my interest. So by Definition 2, the punch is inefficient.
Example 2. I am willing to pay $100 to cut down a tree; you are willing to accept no less than $150 to part with it. By Definition 1, the cutting is inefficient. But part of the reason I’m willing to pay only $100 is that I’m credit constrained. In a world with no transactions costs, I’d borrow more, and would be willing to pay $200 to cut down the tree. So by Definition 2, the cutting is efficient.
Example 3. I am willing to pay $1000 to cut down a tree; you are willing to accept $500 to part with it. By Definition 1, the cutting is efficient. But the only reason I’m willing to pay so much is that I make an excellent living in my job as a mediator who helps people overcome transactions costs. In a world with no transactions costs, I’d be much poorer and would be willing to pay only $200 to cut the tree. So by Definition 2, the cutting is inefficient.
Question: When we say that the law should encourage all and only those actions that are efficient, what, exactly, should we mean?