The dilemma of rules and discretion is ancient and intractable, and it is ubiquitous in the law. Should we govern conduct with relatively precise rules or with discretionary standards that call for the exercise of judgment? Rules generally make matters more predictable; they reduce the danger of arbitrary or discriminatory action; and they are usually easier and less expensive to apply. But rules are invariably crude. They cover some cases that ideally should not be covered, and they fail to cover others that should. For some drivers in some circumstances it is safe to drive faster than fifty-five miles per hour; for others it is not safe to drive that fast. Discretionary standards (“do not exceed a reasonable speed for the conditions”) have the opposite vices and virtues. Ideally they permit the right outcome to be reached in every case. But compared to rules, their application is less certain, and they leave the door open to abuses. There is almost always something to be said for both sides—that’s why it’s a dilemma— although in particular instances it may be possible to figure out that the better solution is a rule, or a discretionary standard, or some combination of the two. Justice Antonin Scalia’s engaging essay The Rule of Law as a Law of Rules covers this familiar ground, but it is an important and influential Article because it does much more.