William  Shakespeare
Sonnet 73


The reader, analysing the layout, can see that in this sonnet there are three quatrain and one coupled at the end.
In this poem, the speaker invokes a series of metaphors to characterize the nature of what he perceives to be his old age.
In the first quatrain, he tells that his age is like a “time of year,” late autumn, when the leaves have almost completely fallen from the trees, and the weather has grown cold, and the birds have left their branches. The first quatrain, which employs the metaphor of the winter day, emphasizes the harshness and emptiness of old age
In the second quatrain, he then says that his age is like late twilight, “As after sunset fadeth in the west,” and the remaining light is slowly extinguished in the darkness. In the second quatrain, the metaphor shifts to that of twilight, and emphasizes  the gradual fading of the light of youth, as “black night” takes away the light.
 In the third quatrain, the speaker compares himself to the glowing remnants of a fire, which lies “on the ashes of his youth”. In the third quatrain, he must resign himself to this fact.
 The image of the fire consumed by the ashes of its youth is significant  for the fact that when the fire is extinguished, it can never be lit again.
In the couplet, the speaker says that he must perceive these things, and that his love must be strengthened by the knowledge that he will soon be parted from the speaker when the speaker, like the fire, is extinguished by time.