In Sonnet 73, Shakespeare has presented a series of metaphor. In the first quatrain, the poet compares his aging to the winter days. He builds a comparison that with the time, he would grow old and pale like the winter days. In the second quatrain, he compares his aging to twilight. He presents the picture of his aging to be a gradual process. The aging has been presented as a gradual process turning from youth to old age. Both the comparisons are different yet their approaches and their conclusion are similar. Both of them talks about old age and falling off of the cycle of life.
