This essay considers the virtue of clarity as a core element of the rule of law. According to the author, its promotion requires a system of separation of powers in which the institution called to create the law is different than the organ called to apply it. In this way, the values of prospectivity, generality and promulgation -directly related to the idea of clarity- are correctly protected and achieved. In contrast, a regime in which the courts have authority not only to adjudicate cases, but also to legislate through judicial decisions, creates areas of uncertainty and retroactivity, both legal vices totally rejected by the very notion of the rule of law.