This poem, a sonnet, consists of fourteen lines of iambic pentameter. The form, which was created by Petrarch, an Italian poet of the fourteenth century, usually consisted of eight lines sketching a situation (octave) and six lines applying it (sestet). The form was modified by Sir Thomas Wyatt and Henry Howard, earl of Surrey. They and other poets created the English sonnet, which consists of three quatrains followed by a couplet, rhyming abab, cdcd, efef, gg. In this form, adopted by Shakespeare and frequently called by his name, the couplet summarizes the theme.

Shakespeare’s sonnets range over many topics, including the beauty of a young man, the desirability of his marriage, a love triangle, a dark lady, and several philosophical and moral concerns. In addition to their poetic power, they remain a unique source of biographical speculation.

Sonnet 73 contains three distinct metaphors for the poet’s progressive aging. The first of these is the implied comparison between his state and the time of year when a few yellow leaves, or none at all, remain on boughs shaking in the cold winds, deserted by the birds that usually inhabit them. One might be tempted to compare this directly with graying and loss of hair, but it is more probably to be taken generally as a reference to the aging process. William Empson has pointed out manifold connotations of the “bare ruined choirs” in his Seven Types of Ambiguity (1930), evoking images of ruined monastery choir stalls made of wood and infused with the atmosphere of stained glass and choirboy charm, showing how that richness is unified by the way that the poet’s subject relates to his narcissistic affection.

The second quatrain moves from the time of year to the time of day. Again there is a metaphor: The poet’s likeness is that of a day fading in the west after sunset. Instead of the yellow of the first quatrain, there is the black of night’s approach, a more sinister prospect. There follows a personification within the metaphor, naming night as death’s second self, in essence creating a new metaphor within the first as it envisions night, which “seals up all in rest.” The word “seals” suggests the permanent closing of a coffin lid, providing a finality that is only slightly relieved by the knowledge that the reader is actually seeing not death, but night. Some critics have suggested that the word “seals” suggests the “seeling” of the eyes of a falcon or hawk, a process of sewing the eyes of the bird so that it would obey the falconer’s instructions more exactly. This suggests an even more forcible entry of death into the metaphor.

Structurally, this concept would close the octave of a Petrarchan sonnet, and although the English sonnet has ostensibly eliminated the eight-six division, the vestiges of a division remain, since the poet moves from his year-day metaphors to another kind of figure in his next quatrain. Here, the metaphor involves a complex process rather than a simple period of time. The afterglow of a fire gradually being choked by the ashes of its earlier burning becomes the description of Shakespeare’s aging. The ashes of the fire’s earlier combustion are the poet’s own youthful dissipation, hinting an extravagance of which we know nothing biographically except the metaphorical statement made here. Although there is no specific color named, one senses the red of a glowing fire, enhancing the yellow and black of the previous descriptions. The concluding couplet moves from metaphor to direct statement, summarizing the purpose of the poet in revealing so frankly his approaching old age. After the richness of the preceding lines, it might appear almost anticlimactic, yet it is important to the structure of the form, lending finality to the whole.