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I don't understand what does " preserve the metre" mean. Could you elaborate? Many thanks
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Most of Shakespeare's work in verse is in what's called
iambic pentameter -
iambic because each bit (it's called a 'foot') is made up of two syllables:
dee-dah (called an 'iamb')
pentameter because there are five of these
feet in each line
For example, from Portia's speech in
the Merchant of Venice,
The qua/lity / of mer/cy is / not strained
It dro/ppeth as/ the gen/tle rain /from heav'n'
Different editions have 'heaven' or "heav'n", but it's clear that Shakespeare wanted the actor to pronounce 'heaven' as one syllable.
In this case, there's a convention in all poetry that 'heaven' is usually pronounced as one sylable (find a site with hymn tunes on it); but in other cases Shakespeare would often drop a syllable so that the elided word would fit in to the metre.
(Note for the interested: by no means all his plays are in iambic pentameter. Sometimes he changes from prose to verse as a signal of what sort of character it is: a king would speak in verse, but a porter wouldn't. Sometimes a person starts to speak in prose, but it becomes verse-like (it has the rythm, but isn't laid out as verse) to mark a change of mood.)