Article 3 of the Constitution takes one of the three categories, boxes, of governmental power, the judicial power, and it vests it in the federal courts, judges who hold tenure during good behavior and have guarantees against diminishment of salary while in office. What is the judicial power? That turns out to be a surprisingly difficult question. If you go to the founding era and you start looking for sources describing what the judicial power is, in crisp, clear terms, you will be sorely disappointed. I know this because I've tried. It's not out there. And once you reflect on it, it becomes clear why you weren't going to find that crisp, clear understanding of judicial power. Until just a few decades before the Constitution, the judicial power was not thought of as a separate box of power. It was part of the executive box of power. People who are fans of John Locke will remember that Locke identified three great heads of governmental power, the legislative power, the executive power, his third was not the judicial power, his third was the federative power, essentially power over foreign affairs, right? So as late as the 17th century, judicial power was just considered part of the executive power. The judges were agents of the crown. Not until the middle of the 18th century did people really start thinking of judicial power as something distinctive, but that means that when Article 3 of the Constitution is ratified, there isn't a big, long, centuries-old tradition of understanding what the judicial power, as distinct from the executive power or even as distinct from the legislative power, entails. And people today still argue about what sets of powers might be incidental to the central case deciding power that the courts have. So articulating exactly what the judicial power is, not an easy task. It's easier. Not easy, but easier, to look at legislative power, executive power and give at least a rough outline of what those look like, though drawing the line between them is not easy as well. Figuring out the line between, let's say, executive and judicial power may be the most difficult line that the Constitution asks us to draw. The thing to keep in mind is it does ask us to draw that line. The entire structure of the Constitution is built around legislative power here, executive power here, judicial power here. It assumes we're going to give it the old college try, and then at least in most cases, we'll be able to come up with something plausible as an answer.