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Walt Whitman and Emily Dickinson are extremely different in terms of the content of their poetry.
Whitman became educated to a higher degree than his parents, but spent a great deal of time after "organized" education to educate himself. He was of the working class, and had several different kinds of job, and a variety of literary experiences. It is then, no surprise, that Whitman developed a strong literary voice based upon the extensive experiences of his life.
Whitman became involved in writing about politics, and at some point, it is uncertain what the particulars are...
As we have noted, Whitman the journalist spoke to the interests of the day and from a particular class perspective when he advanced the interests of white workingmen while seeming, at times, unconcerned about the plight of blacks. [There was] a change that [may have been] intensified by an increasing number of friendships with radical thinkers and writers who led Whitman to rethink his attitudes toward the issue of race. Whatever the cause, in Whitman’s future-oriented poetry blacks become central to his new literary project and central to his understanding of democracy.
...While most people were lining up on one side or another, Whitman placed himself in that space—sometimes violent, sometimes erotic, always volatile—between master and slave.
Whitman became a poet of the people, and changed poetry forever. The world-at-large was his inspiration.
Emily Dickinson is a very different kind of poet; the first reason would be that she was a very different person. Emily was particularly able to observe and understand what was going on around her, although she did not an active social life. Whereas Whitman wrote about the world-at-large, Emily wrote about the microcosm in which she lived: a world she grew up in. In fact:
She was born in a large house built by her grandfather...except for absences of about a year for her schooling and seven months in Boston, she lived in it all of her life and died there...
As with Whitman, she was inspired to write by the world which she occupied. Her work was much more philosophical, dealing with people in her "every day" experiences.
It is paradoxical that a woman who led such a circumscribed and apparently uneventful life managed to acquire the rich perceptions that enabled her to write...poems unlike any others in the English language. ...many are masterpieces. The circumstances of her life, therefore, hold a special fascination for readers of her verse.
Dickinson's sharp perceptions and brilliant inner life arise primarily from her background.
When the Civil War broke out, Emily was greatly influenced by the atmosphere this created, as well as concerns for friends with poor health and involvement of one man in the Union's efforts in the war. Then, between 1874 and 1882, Emily lost six family members and friends, and began to write a great deal about death. By 1886, Emily herself would have passed away.
Whitman's was a strong poetic voice, driven by his experiences out in the world. He wrote about what he saw, and the people he knew. He changed the face of poetry. Even though Emily Dickinson also lived during the same time, her poetry was emerged from the limited circle in which she lived, but her poetry was no less impressive for her lack of life-experience.