The Elements of Verse
The structure of poetry, like that of music, is based on repetition, or regular recurrence of stress. As I have said, the smallest unit of this regularly recurring accent, or stress, is the metrical foot. When we scan a line of verse aloud, we measure these metrical feet to determine the nature of the versification. In this case, we do not hear the rhythm of the phrasing. Meter is like the left hand of the pianist playing a regularly recurring beat; phrasing is like his right hand, weaving all sorts of irregularities over the beat.
Let us take one of Ben Jonson's best-known lyrics:
Still to be neat, still to be drest,
As you were going to a feast;
Still to be powder'd, still perfumed:
Lady, it is to be presumed,
Though art's hid causes are not found,
All is not sweet, all is not sound.
Let us now scan it according to strict meter: