etic ▁v owel ▁to ▁break ▁up ▁con son ant ▁clusters ▁in ▁comp ound ▁words . ▁Within ▁words , ▁ ▁only ▁occurs ▁between ▁similar ▁con son ants , ▁and ▁seems ▁to ▁be ▁explic able ▁as ▁ep enth esis ▁there ▁as ▁well , ▁so ▁that ▁the ▁only ▁underlying ▁v ow els ▁that ▁need ▁to ▁be ▁assumed ▁are ▁. ▁That ▁is , ▁the ▁N du ▁ ▁languages ▁may ▁be ▁a ▁rare ▁case ▁of ▁a ▁two - v owel ▁system , ▁the ▁others ▁being ▁the ▁Arr ern te ▁and ▁North west ▁C au cas ian ▁languages . ▁However , ▁contrast ing ▁anal ys es ▁of ▁these ▁same ▁languages ▁may ▁posit ▁a ▁dozen ▁v owel ▁mon oph th ongs . ▁ ▁For ▁N du ▁languages , ▁the ▁gl ott al ized ▁low ▁v owel ▁ ▁is ▁often ▁written ▁as ▁. ▁This ▁does ▁not ▁sign ify ▁ ▁followed ▁by ▁a ▁gl ott al ▁stop ▁and ▁another ▁. ▁ ▁Mor ph ology ▁N du ▁languages ▁mark ▁first ▁and ▁second ▁person ▁possess ors ▁with ▁- n , ▁and ▁third ▁person ▁possess ors ▁with ▁- k . ▁Am bul as ▁w un ɨ - n ə ▁m bal ɨ ▁ 1 SG - PO SS ▁p ig ▁‘ my ▁p ig ’ ▁▁ nd ɨ - ku ▁m bal ɨ ▁ 3 SG - PO SS ▁p ig ▁‘ his ▁p ig ’ ▁ ▁Man amb u ▁w un -( n ) a ▁ma ː m ▁ 1 SG - PO SS ▁older . s ib ling ▁‘ my ▁elder ▁sister ’