What is the rhyme scheme and its analysis in Shakespeare’s "Sonnet 20"?

Shakespeare’s “Sonnet 20” follows a very standard rhyme scheme for the sonnets. The poem is divided into four parts, three of them quatrains followed by a two-line refrain at the end of the poem. In total, there are 14 lines, and they follow a very standard set of rhyming rules.
The first three stanzas, the quatrains, are written in an alternating rhyming scheme. This means that the first and third lines rhyme, as well as the second and fourth lines. This creates an alternating rhythm in each stanza, connecting each line not to the one immediately following it but the subsequent one. The rhyme scheme gives structure and continuity through each quatrain while not leaving it stilted, connecting only in couplets.
The repeated structure of the quatrain for each of the three stanzas gives a similar and cohesive feeling. This rhyming scheme and rhythm ties the stanzas together, helping the reader feel the connection and rhythm throughout the first three stanzas. As the lines ebb and flow between one rhyme and the next, it gives the semblance of ambulation, as if the reader is walking somewhere, which builds up anticipation throughout the final quatrain.
Eventually, the scheme ends and a final refrain is introduced—two simple lines with a shared rhyme. This is the resolution to the poem, giving a finality that concludes the meter of the poetry, ending the feeling of motion. By concluding it in this manner, there is an abrupt and definitive end that diverges from, while also enhancing, the prior stanzas.
The poem is playful and has somewhat overt sexual overtones, making it rather shocking for the historical reader. This rhyming pattern illuminates the playful qualities of the poem and helps to guide gentle and humorous rhymes together without having to be too obvious. By splitting the rhymes, Shakespeare buried the lead and makes the humor of the poem more surprising.