(cf SCR Part 8, rule 1; DCR Part 7, rule 1; LCR Part 6, rule 1)
(1) In any originating process, the plaintiff may claim relief against the defendant in respect of more than one cause of action in any of the following circumstances--(a) if the plaintiff sues in the same capacity, and claims the defendant to be liable in the same capacity, in respect of each cause of action,(b) if the plaintiff sues--(i) in his or her capacity as executor of the will of a deceased person, or administrator of the estate of a deceased person, in respect of one or more of the causes of action, and(ii) in his or her personal capacity, but with reference to the estate of the same deceased person, in respect of the remaining causes of action,(c) if the plaintiff claims the defendant to be liable--(i) in his or her capacity as executor of the will of a deceased person, or administrator of the estate of a deceased person, in respect of one or more of the causes of action, and(ii) in his or her personal capacity, and in relation to the estate of the same deceased person, in respect of the remaining causes of action,(d) if the court grants leave for all of the causes of action to be dealt with in the same proceedings.
(2) Leave under subrule (1) may be granted before or after the originating process is filed.