Provident Tradesmens Bank & Trust Co. v. Patterson
United States Supreme Court
390 U.S. 102 (1968)
After Cionci, driving Dutcher's car with permission for an errand, caused a fatal accident, Lynch's estate administrator Provident Tradesmens Bank (plaintiff) sued Lumbermens (Dutcher's insurer) and Cionci's estate (defendants) seeking a declaration that Cionci had permission to use the car and was covered by Lumbermens' policy; the district court found in Provident's favor, but the Third Circuit reversed on the ground that Dutcher, whose personal liability depended on the coverage question, had to be joined -- a joinder that would have destroyed diversity jurisdiction.
Whether a person's right to be joined as a party is a substantive right that categorically prevents a court from proceeding without him when he might be affected by the judgment.