Today I ran across this passage in an older equity treatise. 1 Robert Treat Whitehouse, Equity Practice: State and Federal 92-96 (1915) (emphases added):
§ 59. Numerous persons. The cases where of numerous persons having a material interest, a portion may be dispensed with as parties, rest on the principle of virtual representation, i. e., the principle that where a large number of persons have a common interest, a portion of the number bringing a bill or defending in behalf of themselves or others may fairly be taken to represent the whole so that a decree can be rendered in the case without prejudice to the rights of the absent. The interest in question must be a community of interest in the subject matter of the suit, i. e., in the estate, title or right involved in the controversy, and it matters not whether it be a community of interest in the same property or separate and distinct property interests having a common interest in the enforcement or defeat of the right involved in the controversy, provided that the success of the portion bringing the bill or defending in behalf of the others will benefit all alike. But in such case, the bill must be brought in behalf of the plaintiff and all others of like interest, and it should be alleged in the bill that it is thus brought since the parties are too numerous to do otherwise. If brought solely in behalf of the plaintiff, or nominally in behalf of all, but seeking to establish an individual right of the plaintiff’s, adverse and exclusive in its nature, all whose interests will be affected must be made technical parties or the bill will not be sustained. The rights of the absent ones can only be bound by the decree of the court where all have a common interest so that a portion before the court may fairly be taken to represent all.
The chief classes of cases of numerous persons represented by a few are creditors’ bill, stockholder” bills and bills of peace.
This passage is a good exposition of the older equity practice. It also shows why the modern class action is the lineal descendant of these older equity group actions. There is no longer any room in the federal system for some other form of virtual representation that evades the requirements of the class action (cf. Taylor v. Sturgell). Once that is recognized, there’s no room for the national injunction, which is a way of getting the benefit of a class action while evading all the requirements.