bar ▁phr ases , ▁A , ▁B , ▁and ▁C , ▁played ▁in ▁the ▁following ▁order : ▁AB ▁A BB ▁AB ▁C ▁Ir regular ▁– ▁The ▁theme ▁or ▁ground ▁does ▁not ▁fit ▁into ▁any ▁of ▁the ▁above ▁structures . ▁ ▁F ew ▁p ib ro chs ▁are ▁pure ▁examples ▁of ▁any ▁of ▁these ▁structures ▁though ▁most ▁can ▁be ▁fit ▁into ▁one ▁of ▁the ▁first ▁three ▁with ▁a ▁slight ▁modification ▁of ▁one ▁or ▁two ▁of ▁the ▁phr ases ▁in ▁one ▁or ▁more ▁lines . ▁ ▁A ▁compilation ▁of ▁the ▁structure ▁of ▁many ▁p ib ro ch ▁t unes , ▁including ▁related ▁historical ▁ess ays , ▁was ▁written ▁by ▁A . ▁J . ▁H add ow . ▁ ▁There ▁is ▁evidence ▁from ▁early ▁treat ises ▁( e . g . ▁Joseph ▁Mac Donald ) ▁that ▁the ▁structure ▁was ▁originally ▁counted ▁in ▁ 4 , ▁so ▁a ▁Primary ▁form ▁would ▁be ▁A AB A ▁BB AB ▁ ▁Similarly , ▁Second ary ▁form ▁can ▁be ▁read ▁as ▁ab AB A ▁ba B AB ▁ ▁Tit les ▁and ▁subjects ▁ ▁The ▁G ael ic ▁titles ▁of ▁p ib ro ch ▁compos itions ▁have ▁been ▁categor ised ▁by ▁R oder ick ▁C annon ▁into ▁four ▁broad ▁group ings . ▁These ▁include : ▁▁ ▁Function al ▁– ▁sal utes , ▁l aments , ▁march es ▁and ▁gather ings . ▁ ▁Techn ical ▁– ▁referring ▁to ▁strictly ▁musical ▁characteristics ▁of ▁the ▁pieces ▁such ▁as ▁" port " ▁or ▁" g las ", ▁terms ▁shared ▁with ▁wire - str ung ▁har pers