RCW 59.12.140: Proof in forcible entry and detainer.

On the trial of any proceeding for any forcible entry or forcible detainer the plaintiff shall only be required to show, in addition to a forcible entry complained of, that he or she was peaceably in the actual possession at the time of the forcible entry; or, in addition to a forcible detainer complained of, that he or she was entitled to the possession at the time of the forcible detainer.