Consider this famous example from Rigoletto:
La donna e m ` obile
Qual piuma al vento,
Muta d’accento
E di pensier.
Allfourlines arequinari.Thefirst,however,hassix syllables,termedquinario
sdrucciolo since the final accent falls on the antepenultimate syllable. The
second and third lines have five syllables, the accent falling on the penultimate, and are termed quinario piano, the standard type. The fourth has four
syllables, the accent falling on the last syllable: quinario tronco. Note that in
singing the words “donna e” and “piuma al,” the adjacent vowels fuse into `
a single syllable in an effect of elision (sinalefe).
These principles hold for other meters. In all cases, save the two longest
lines (decasillabo and endecasillabo), “double” forms (doppio) also exist,
for example quinario doppio (not to be confused with decasillabo, which
has a different pattern of accents). In general, accents in lines that have an
even number of syllables (senario, ottonario, and decasillabo) recur in fixed
positions, giving those meters regularity and predictability; longer lines
with an odd number of syllables (settenario and endecasillabo) have greater
flexibility.
