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The first step in writing anything in response to Walt Whitman's "Song of Myself," is to try to understand what the poet is saying in general. My perception is that while he describes himself in many settings or different contexts (pay attention to nature, as he does), what matters is not possessions that surrounds him, but what comes from him: what is unique to the man known as Walt Whitman. He describes his connection to the world, past and present. He also has a great love of nature. At the same time, he seems to acknowledge that his uniqueness is found also in other people: as they, too, are unique.
I celebrate myself, and sing myself,
And what I assume you shall assume,
For every atom belonging to me as good belongs to you.
I would note also that the organization Whitman uses to start the poem deals with who he is based upon his experiences, and things very basic to his physical essence.
First, he speaks of school and things that have "touched" him there:
Creeds and schools in abeyance,
Retiring back a while sufficed at what they are, but never forgotten,
I harbor for good or bad...
Then he notes that while he is exposed to things in his environment, those that are most meaningful are things that connect with him— his make-up:
I breathe the fragrance myself and know it and like it...
He is aware of what occurs around him, and these things shape his thoughts and perceptions, but this "song" is about him and the natural world, not the perfume of rooms, etc.
In order to write your essay on this work, recognize that his "song" does not refer to material things. Whitman refers to things such as his smell and his taste, referring to very basic aspects of his physical self. If I were writing this essay, I would concentrate on the aspect of himself that he presents in the poem, find a central theme in each section, and try to acknowledge the organization, which he uses. For example, he starts with small, sensory details and descriptions; does he continue this way throughout the "song" or does he change his focus?
Merriam-Webster.com defines "explicate" as:
...to give a detailed explanation of
So you are asked to explicate or "explain" what the poem means. As you do this remember a couple of things. First, poetry (and all literature) speaks differently to each of us depending upon our life experiences; secondly, look up words you may not know. Third, do not pause in reading when the line ends unless there is a period, comma, etc. Without end punctuation, the line continues directly to the next line: follow these "signals" for easier comprehension. Also, make use of eNotes source materials. Several links are listed below.