The preceding chapters on the federal joinder rules describe a highly flexible system that liberally allows parties to expand the litigation by joining claims in a single action. However, permission under the joinder rules to assert a claim, while necessary, is not sufficient to allow the court to hear it: From early on, we have seen that the court must always have subject matter jurisdiction over a claim if it is to proceed. As you have already read---and you will hear it repeated ad nauseum for the rest of your professional life---the subject matter jurisdiction of the federal courts is limited to the categories of cases enumerated in Article III, §2, of the Constitution.
These two principles, broad joinder under the Rules of Civil Procedure and the need for subject matter jurisdiction over every claim, are on something of a collision course. Frequently, the rules will authorize joinder of claims over which there is no independent basis of subject matter jurisdiction. Such cases pose a dilemma for the courts: The efficiency goals of the Rules favor inclusion of related claims, but the ineluctable need for subject matter jurisdiction appears to bar the court from hearing them.