Rhyming Lines of Iambic Tetrameter
In the context of the play, "Spring" is a song. It gets its song-like sound from a number of factors, but rhyme
and meter are two of the biggest. The song is written in iambic tetrameter with a very strong, regular rhyme scheme.
Sorry about that—for all you normal folks in the crowd who aren't fluent in prosody-speak, let us translate:
Did you notice how the lines kind of gallop along in a very rhythmic daDUM daDUM kind of way? What you're hearing is the poem's meter. That pattern of an unstressed syllable followed by a stressed syllable is called an iamb. If you put four of those little daDUM units together in one line you have what is known in the poetry world as "iambic tetrameter," which is just a fancy way of saying that you have four iambs in a line. Here are a couple lines of iambic tetrameter in action. Read them aloud and listen:
When daisies pied and violets blue
And lady-smocks all silver-white. (1-2)
Hear it? Good. Now you're fluent.
In addition to that bouncy meter, "Spring" also has a super-regular rhyme scheme. This pattern makes the auditory connection between the rhyming end words even stronger and helps make the song feel like a song. The rhyme scheme in the first stanza is ABABCCADD:
The poem's second stanza has a nearly identical rhyme scheme, but there's one minor variation. See if you can spot it. Got it? Good. So, the stanza 2 end words follow this pattern—ABABCCBDD:
Wait. Stop yelling at your computer screen. It's not a good look. We're aware that "clock" and "smock" do not rhyme with "cuckoo." So, you ask, why are they all designated in the rhyme scheme as "B"? Excellent question.
What we have here is a case of slant rhyme. Yeah, it's a real thing. With slant rhyme, the words almost rhyme but not quite. They share some sounds (like those hard Cs and CKs) but they never quite make it to full rhyme status.
Now, we know what you're thinking: "What gives, Will? Why the weak rhyme?" Here's the thing: Shakespeare was one of the original rhyme masters. If he wanted to, he certainly could have dropped a serious full rhyme instead of the slant rhyme. He did it for a reason.
By using slant rhyme in this case, Shakespeare was able to let the song's form mirror the content. The song is about an unexpected aspect of spring. It gives us an idyllic scene but the scene brings to mind a less than idyllic situation (remember that cuckoo-cuckold connection?). So, instead of having perfect rhymes throughout the entire poem, Shakespeare slips in a slant rhyme mirroring the surprise and unease that the cuckoo's song inspires in all those "married men."
Just like those married dudes start getting the feeling that something is a little off when they hear the cuckoo's song, the reader feels slightly jarred by the slant rhyme amid all those other perfect rhymes. Well played Will, well played.