In the poem "On the Subway" written by Sharon Olds, there is occasionally a shift in tone as Olds explores different contrasts and connections between the black "mugger" and the white observer. Most of these tone shifts are caused by caesuras, which separate different parts of the poem but serve to keep the flow going and offering that those different parts may be connected.
The first part is the observation phase. This is when the observer and the "mugger" "face each other" in the subway, while the observer describes the two of them. This passage contains subtleties that will be explained further in the poem. For example the two stand at "opposite ends" of the subway. They represent opposite ends of the racial spectrum. The "mugger"'s hoodie is described as being "red, like the inside of a body exposed", while the observer is wearing "the whole skin of an animal taken and used". It is almost as if the observer has stolen the black man's skin and used it for her own protection. She is doubly protected against America's racist heart while the black man has no protection. This theme of theft seems ironic considering that the black man is described as a "mugger".
The next part, starting at "used. I look at his raw face", is about power and security. Unlike the first part, the second part's descriptions are less subtle: it is clear to see that in certain ways the observer is in the black man's power and in other ways the black man is in the observer's power. However we begin to see a difference between the choices of the individual and society: The observer's fear of the black man is a personal description. She is afraid the black man might mug him. However the observer's sense of power over the black man describes not the individual difference between them but how they are placed as a society. The group in society that the white woman belongs to is feeding off the group that the black man belongs to, "eating the steak he does not eat". Since this is an aspect of society, not an aspect of the individual, there is nothing she can do to change it if she is to remain within the bounds of her society. It is interesting to note that the theme of theft now ties with the theme of society: as an individual the black man is the one who might steal from the white woman, however as a society white people are stealing from black people constantly.
In some ways the last part, beginning with another caesura, "mouth. And he is black and I am white" presents a 'cliff face' to the reflections discussed in the previous paragraph. In other words all the subtleties discovered before have been revealed as true in this paragraph. This paragraph describes how the black man's skin gives him a permanent place in society which "absorbs the murderous beams of the nation's heart" while the white woman's skin reflects them. The connection between the black man and a "seedling" further emphasizes the fact that his blackness is a fact about him that he has owned since birth. Neither of them cannot change what they are.
In conclusion, breaking the poem into sections with caesurae serve to help the reader adress the poem in various different parts, however because caesurae encourage the reader to read on there is no stopping between parts, therefore helping the reader to draw connections between the parts in order to adress prevalent themes in the poem such as theft and the difference between the choices of the individual and the choices of the society. In addition Olds helps the poet understand these themes better with the use of an ending "cliff face" section.
