In words coming from Middle English, most cases of the Modern English diphthongs originate from the Middle English long monophthongs through the Great Vowel Shift, although some cases of originate from the Middle English diphthongs .
In wordS comiNg From midDLe ENglish, mosT Cases of THe MoDeRn EnGLISh diphThOnGS ORIginaTE From The middLE eNglisH lONg monophThongs tHRoUgh thE Great VowEL shIft, ALthough Some casEs of oriGINate frOM The MIdDLe EnGLisH diphthOngs 