The 14 lines of the Shakespearean sonnet is formed by using 3 quatrains (4 lines of verse x 3 repetitions = 12 lines) and 1 couplet (2 lines) to result in the required 14 lines. Usually, there is a problem expressed in the first three quatrains, which is then resolved by the closing couplet
Include 14 lines of equal length. The sonnet is known for its length: 14 lines exactly. There are many varieties of the sonnet form, but Shakespearean sonnets are always 14 lines. The quatrain is a poetic term for 4 lines of poetry that share a common sensibility, and usually share a rhyme scheme. The couplet is a poetic term for 2 lines of rhyming verse. The 14 lines of the Shakespearean sonnet is formed by using 3 quatrains (4 lines of verse x 3 repetitions = 12 lines) and 1 couplet (2 lines) to result in the required 14 lines.
Usually, there is a problem expressed in the first three quatrains, which is then resolved by the closing couplet.
Each quatrain extends a thought or idea expressed in the preceding quatrain.