What is the difference between a cause of action and a complaint in intervention?

The existence of a single, rather than a separate, cause of action was discussed in Bosworth v. Superior Court (1956) 143 Cal.App.2d 775, 300 P.2d 155, where the complaint in intervention was dismissed for failure to prosecute. In Bosworth, the original plaintiff, an heir, brought an action to cancel a deed of property to the defendants. The administrator of the property filed a complaint in intervention alleging the same cause of action and seeking the same relief as the heir. The court held that the time for bringing the administrator's action to trial commenced with the filing of the original complaint by the heir. The court reasoned, "The cause of action asserted by the complaint in intervention is the same cause of action as asserted by the complaint. It follows that the complaint in intervention was not a prosecution of a different action but merely a step in the prosecution of the original action, and that the five-year period commenced to run upon filing of the original complaint." (Id. at p. 779, 300 P.2d 155.)