Sonnet XVIII
Considering the title, the reader can understand that the Sonnet XVIII is part of a collection. It is composed by three quatrains and a couplet: it follows the structure of the Elizabethan-Shakespearian sonnet. It is dedicated to the fair youth, like the most of Shakespearian sonnets.
The sonnet is lyric because the poet talks about personal things.
The poet uses the semantic fields of time and nature.
The sonnet opens with a dialogue between the poet and a "thee", that means "you". The poet describes the "thee": he is more lovely, temperate and pleasant than a summer day.
Shakespeare idealizes the Youth and compares him to the summer.
The poet is worried because of the time, that will bring the beauty of the Fair Youth away.
The rhyming cuplet presents a possible solution: the poet can write verses to make the Fair Youth immortal.