The sonnet is a fourteen-line poem composed in iambic pentameter with one of many rhyme schemes and a strictly ordered thematic framework. The name derives from the Italian word sonetto, which means "a little sound or song." Although the term may suggest that a sonnet must be concise, most are not. Indeed, some sonnets are so lengthy as to be impractical.
A sonnet form is typical of poems that use a regular meter (and therefore can be described as "sonnet-like") but it is not exclusive to such poems. Many other kinds of poems also use this form; for example, Shakespeare's 154 sonnets are generally accepted to be written in sonnet form although they were not called such at the time they were written. Other notable sonnets include those by William Wordsworth, Robert Browning, and Elizabeth Barrett Browning.
In modern usage, the term "sonnet" usually refers to a poem that follows the formal structure of the sonnet. However, during its early history the term was not defined specifically and thus many other types of poetry could be called "sonnets". For example, one found in medieval England was the complaint, which was also called a "petition" or "allegory". These poems often began with the phrase "As who would say..." and sometimes ended with the same line repeated three times.
A sonnet is a fourteen-line poem that uses one of many formal rhyme patterns. A poem is a piece of literature in which the expression of sentiments and ideas is given emphasis via the use of language, rhyme, rhythm, and imagery. Sonnets were popular in Europe from the late 14th century to the early 17th century, when they were eclipsed by poems written in English's successor form, iambic pentameter.
Sonnets share with other forms of poetry such as limericks, haikus, and villanelles a concern for meter, rhyme, and alliteration. They differ mainly in length: a typical sonnet requires between fourteen and twenty-two lines to be complete. Many short poems have been called "sonnets", such as Shakespeare's sixteenth-century work, but most do not follow the strict pattern of the form. Modern scholars generally agree that Shakespeare's sonnets are distinct enough from other poetic sequences of the time to be considered examples of their own genre.
Apart from length, there are two other main differences between sonnets and other kinds of poems: their theme and their form. Sonnets often deal with love, although this is not always the case. They usually have a structure that follows a pattern of some kind, which can be repeated as many times as necessary.
Sonnet 18 is a conventional English or Shakespearean sonnet, with 14 lines in iambic pentameter divided into three quatrains and a couplet. It also contains the usual rhyme scheme: ABAB CDCD EFEF GG. The poem is inspired by the rhetorical tradition of the Italian or Petrarchan Sonnet. This type of poem typically uses an enigma or mystery to attract readers, who try to solve the riddle by reading between the lines.
The first line states that "love is blind". This can be interpreted as love not seeing what love has done to him/herself. Or it can be taken more literally, as love cannot see itself. Either way, the sonnet is saying that love is irrational.
The second line states that "love looks on the outward show". Again, this can be taken two ways. It could mean that love looks at someone's appearance and finds their beauty attractive, but not their soul. Or it could mean that love only cares about what people do or don't have - money, status, fame - and not how they feel inside.
In the third line, the poet says that love is blind. This can be interpreted as meaning that love cannot see what everyone else sees - that love is blind to other people's opinions of it. Or it could mean that love is blind to its own true intentions. Either way, the poem is saying that love is irrational.