which ▁officially ▁sign ifies ▁a ▁near - open ▁front ▁un r ounded ▁v owel ). ▁This ▁is ▁the ▁usual ▁practice , ▁for ▁example , ▁in ▁the ▁historical ▁study ▁of ▁the ▁English ▁language . ▁The ▁loss ▁of ▁separate ▁symbols ▁for ▁open ▁and ▁near - open ▁front ▁v ow els ▁is ▁usually ▁considered ▁un problem atic , ▁because ▁the ▁per cept ual ▁difference ▁between ▁the ▁two ▁is ▁quite ▁small , ▁and ▁very ▁few ▁languages ▁contrast ▁the ▁two . ▁If ▁there ▁is ▁a ▁need ▁to ▁specify ▁the ▁back ness ▁of ▁the ▁v owel ▁as ▁fully ▁front ▁one ▁can ▁use ▁the ▁symbol ▁, ▁which ▁denotes ▁a ▁lower ed ▁near - open ▁front ▁un r ounded ▁v owel . ▁ ▁The ▁Ham ont ▁dialect ▁of ▁Lim burg ish ▁has ▁been ▁reported ▁to ▁contrast ▁long ▁open ▁front , ▁central ▁and ▁back ▁un r ounded ▁v ow els . ▁This ▁is ▁extremely ▁unusual . ▁ ▁Fe atures ▁▁ ▁This ▁sub sum es ▁central ▁open ▁( central ▁low ) ▁v ow els ▁because ▁the ▁tongue ▁does ▁not ▁have ▁as ▁much ▁flex ibility ▁in ▁position ing ▁as ▁it ▁does ▁in ▁the ▁mid ▁and ▁close ▁( high ) ▁v ow els ; ▁the ▁difference ▁between ▁an ▁open ▁front ▁v owel ▁and ▁an ▁open ▁back ▁v owel ▁is ▁similar ▁to ▁the ▁difference ▁between ▁a ▁close ▁front ▁and ▁a ▁close ▁central ▁v owel , ▁or ▁a ▁close ▁central ▁and ▁a ▁close ▁back ▁v owel . ▁ ▁Occ urrence ▁Many ▁languages ▁have ▁some ▁form ▁of ▁an ▁un r ounded ▁open ▁v owel . ▁For ▁languages ▁that