Ibar yempahla, ekwaziwa ngokuba sisivalo somthwalo okanye isitshixo somthwalo, sisixhobo esibalulekileyo kwindawo yezothutho kunye nolungiselelo.Eyona njongo yayo kukukhusela kunye nokuzinzisa imithwalo ngaphakathi kwiilori, iitreyila, okanye izikhongozeli zokuthumela ngenqanawa ngexesha lokuhamba.Le mivalo iyahlengahlengiswa kwaye ngokuqhelekileyo yandisa ngokuthe tye phakathi kweendonga zendawo yempahla, idala umqobo othintela iimpahla ekutshintsheni, ukuwa, okanye ukonakala ngexesha lokuthutha.Imivalo yemithwalo ibalulekile ekugcineni intembeko yokuthunyelwa kwempahla, ukuqinisekisa ukuhanjiswa kwempahla ngokukhuselekileyo nangokufanelekileyo, kunye nokunciphisa umngcipheko womonakalo okanye ilahleko ngexesha lokuhamba.Ngokuguquguquka kwazo kunye nokusebenziseka ngokulula, imivalo yemithwalo idlala indima ephambili ekuphuculeni ulungelelwaniso lwamashishini ahlukeneyo, igalelo kukhuseleko olupheleleyo kunye nokuthembeka kwenkqubo yothutho.