In the text below, I've retained the spelling as "Silvia", although it is sometimes recast as "Sylvia". Silvia is a pretty young lady who is sought after by quite a lot of young swains, including the pair of friends at the start of the book, Valentine and Proteus (who has already exchanged rings and vows with the fair Julia, who turns up in drag as Sebastian). This song is performed outside her tower window by musicians, hired by yet another guy (Thurio, Silvia's father's choice of suitor) in order to woo her.
Who is Silvia?
by William Shakespeare
Who is Silvia? what is she,
That all our swains commend her?
Holy, fair and wise is she;
The heaven such grace did lend her,
That she might admirèd be.
Is she kind as she is fair?
For beauty lives with kindness.
Love doth to her eyes repair,
To help him of his blindness,
And, being helped, inhabits there.
Then to Silvia let us sing,
That Silvia is excelling;
She excels each mortal thing
Upon the dull earth dwelling:
To her let us garlands bring.
Analysis of form: The song is organized into three five-line stanzas. Each of the stanzas uses the rhyme scheme of ABABA within it, including the third stanza. While you might, at a glance, note the "-ings" in all five lines the A lines are a simple "-ing", while the B lines are "-elling" endings.
The A lines are all written in trochaic meter with a truncated (or masculine) ending or, if you prefer, consist of two trochees (DUM-ta) followed by an amphimacer or cretic foot (DUM-ta-DUM). Regardless what you call it, the stress pattern alternates, starting and ending with a stressed syllable: DUM-ta DUM-ta DUM-ta DUM.
The B lines are opposite - either iambic meter with a truncated (feminine) ending or, if you prefer, two iambs (ta-DUM) followed by an amphibrach (ta-DUM-ta). Either way, you have alternating stress patterns, starting and ending with an UNstressed syllable: ta-DUM ta-DUM ta-DUM ta.
Franz Schubert did a setting of this song, known in German as An Silvia, and in English as Who is Silvia?, which can be found in a host of performances on YouTube and elsewhere. Here's a rather dizzyinv video that "reads along" with the lyrics auf Deutsch while a recording by one of my favorite baritones ever, Dietrich Fischer-Dieskau, sings to a simple piano accompaniment by Gerald Moore. Seriously, it doesn't get much better than that pairing when it comes to art songs. But again, I digress:
Steve Winwood did a bit of a rewrite and came up with Silvia (Who is She?) on his 2003 album About Time. The song also appeared (evidently) as part of a musical called Shakespeare, Sonnets, and Rock 'n' Roll, which I wish I'd known about before today. But I have found it out on the YouTube, and present this song (which starts after a few sentences of introduction by the lead singer):