The characteristics of a sonnet are its rhyme scheme, its metric structure, its common topics, and its specific cultural conventions. This type of poem traditionally has a strict number of lines with ending words that must rhyme according to a certain formula. These literature rules determine whether a piece of poetry is classified as a sonnet rather than as another type of poetry such as blank verse. Sonnets also have a few variations according to their authors' backgrounds, but these structural differences still need to fall within specific parameters. Language scholars generally believe that this kind of written verse originated from an Italian form of poetry called the sonetto that was recited to musical accompaniment, which accounts for this type of poetry's uniform rhythmic characteristics.
Each line of a sonnet is written with precisely 10 beats and an arrangement of words with alternating syllable stresses. The first syllable of the first word is unstressed, followed by a stressed syllable and then another unstressed syllable. A complete line in this poetry form contains exactly five unstressed and five stressed syllables. This metric structure is known as iambic pentameter, and its distinctive rhythm is intended to mimic that of the human heartbeat. Poetry written in this well-known form is frequently designated the Shakespearean sonnet style.
A sonnet contains four sets of verse called quatrains that consist of four lines each. The first three quatrains have four lines and the final quatrain has only two lines, which also serves as the closing verse that sums up the entire theme of the poem. All four quatrains total 14 lines of poetry, and the ending words of each line need to follow a specific rhyme pattern. The final word of the first line of a sonnet needs to rhyme with the final word of the third line. This alternating rhyme scheme continues through the rest of the poem with a different rhyme sound for each of the first three quatrains.
Topics of a sonnet are often centered around love, war, and human mortality, though these can vary according to the poet's preferences as well as cultural background. The common themes of an English poem can often be different from those of an Italian one, and the rhyme schemes of each can also sometimes differ according to established conventions. One notable distinction is that an Italian sonnet usually does not end with the same two concluding lines that are also called a couplet.