What is the proper definition of a cause of action?

The proper definition of the term, “cause of action,” is somewhat elusive even though lawyers and judges routinely use it. One current use of the term reflects the basic underlying policy thrust that a plaintiff suing a defendant for relief in respect of a single event must do so in one lawsuit: Cahoon v. Franks, 1967 CanLII 77 (SCC), [1967] S.C.R. 455 per Hall J. at page 457. As Williston and Rolls observe in The Law of Civil Procedure (Toronto: Butterworths, 1970) at 398: Because there is now only one cause of action which might cause different types of damages, all claims for damage must be asserted in one action. The institution of another action would be an abuse of process…