A sonnet is a 14-line poem. The English or Shakespearean sonnet differs from the Petrarchan sonnet in that it consists of three quatrains followed by a concluding couplet. Like all of William Shakespeare’s sonnets, “Sonnet 104” is written in iambic pentameter. An iamb is a poetic foot that consists of an unstressed syllable followed by a stressed syllable. A pentameter comprises five poetic feet in one line, so iambic pentameter contains 10 syllables per line. Line 2 presents an example, “For as | you were | when first | your eye | I eyed,” as does Line 6, “In pro | cess of | the seas | ons have | I seen.” Line 5, “Three beaut | eous springs | to yell | ow aut | umn turned,” is also in iambic pentameter; the word “beauteous” is pronounced as two syllables rather than three.

Shakespeare employs frequent variations on the iambic meter. In Line 1, for example, he uses a spondee rather than an iamb in the second foot. A spondee consists of two stressed syllables: “fair friend.” The effect for the reader is that this spondaic foot stands out against the expected iambic metrical base and so provides an emphasis.