This section is from the book "Popular Law Library Vol7 Equity Jurisprudence, Trusts, Equity Pleading", by Albert H. Putney. Also available from Amazon: Popular Law-Dictionary.
At common law, while there may be any number of either plaintiffs or defendants, provided the interests of all such plaintiffs or all such defendants are either joint or common, there is no method by which three or more mutually adverse interests may be adjudicated in the same suit. In equity any number of mutually adverse interests, relating to the same subject matter, may be adjudicated in the same suit. Thus in a suit to foreclose a first mortgage, the mortgagor, his assignee, a second mortgagee, a judgment creditor of the mortgagor and all others holding any interest in the property may be joined as defendants.
Equity will also compel a plaintiff in proper cases to consolidate his various claims against the defendant, in order to prevent the latter from being barred by a multiplicity of suits, and will ever in extrinsic cases compel different plaintiffs with common interests to consolidate the claims, or enjoin the prosecutions of other suits until the first and test suit is determined.
Equity will also prevent a multiplicity of suits by taking complete jurisdiction where both an equitable and legal remedy is required.
Bills of interpleader, another method of preventing multiplicity of suits, will be considered in a later chapter.