"Middle English" is a subset of English. Middle English is the
type of English spoken in Chaucer's time, as in _The Canterbury
Tales_. English is a language as a whole, but over time, the
dialect has changed from Old English, the dialect spoken in
_Beowulf_, to Middle English, the dialect spoken in Chaucer's time,
in _The Canterbury Tales_, to Modern English, the dialect spoken in
Shakespeare's time, in _Hamlet_, to today's English, the dialect
I'm writing in right now.