▁for ▁impro vis ation . ▁ ▁Rock ▁music , ▁and ▁other ▁forms ▁of ▁popular ▁music ▁and ▁folk ▁music ▁tend ▁to ▁pick ▁one ▁or ▁two ▁mel od ies ▁( verse ▁and ▁ch orus , ▁sometimes ▁with ▁a ▁third , ▁contrast ing ▁mel ody ▁known ▁as ▁a ▁bridge ▁or ▁middle ▁eight ) ▁and ▁stick ▁with ▁them ; ▁much ▁variety ▁may ▁occur ▁in ▁the ▁phr asing ▁and ▁lyr ics . ▁Indian ▁classical ▁music ▁re lies ▁heavily ▁on ▁mel ody ▁and ▁rh ythm , ▁and ▁not ▁so ▁much ▁on ▁harm ony , ▁as ▁the ▁music ▁contains ▁no ▁ch ord ▁changes . ▁Bal inese ▁gam el an ▁music ▁often ▁uses ▁complicated ▁variations ▁and ▁alter ations ▁of ▁a ▁single ▁mel ody ▁played ▁simultaneously , ▁called ▁heter oph ony . ▁In ▁western ▁classical ▁music , ▁compos ers ▁often ▁introduce ▁an ▁initial ▁mel ody , ▁or ▁theme , ▁and ▁then ▁create ▁variations . ▁Class ical ▁music ▁often ▁has ▁several ▁mel od ic ▁layers , ▁called ▁poly phony , ▁such ▁as ▁those ▁in ▁a ▁fug ue , ▁a ▁type ▁of ▁counter point . ▁O ften , ▁mel od ies ▁are ▁constructed ▁from ▁mot ifs ▁or ▁short ▁mel od ic ▁fragments , ▁such ▁as ▁the ▁opening ▁of ▁Be eth oven ' s ▁Fif th ▁Sym phony . ▁Richard ▁Wagner ▁popular ized ▁the ▁concept ▁of ▁a ▁le it mot if : ▁a ▁mot if ▁or ▁mel ody ▁associated ▁with ▁a ▁certain ▁idea , ▁person ▁or ▁place . ▁While ▁in ▁both ▁most ▁popular ▁music ▁and ▁classical ▁music ▁of ▁the ▁common ▁practice ▁period ▁pitch ▁and ▁duration