A contemporary of Emily Dickinson, Ralph Waldo Emerson, wrote in his essay Self-Reliance,
Society everywhere is in conspiracy against the manhood of every one of its members....The virtue in most request is conformity. Self-reliance is its aversion. It loves not realities and creators, but names and customs.
Like Emerson, Ms. Dickinson strongly valued her independence of thought, and led a reclusive life, deliberately choosing solitude in which to write her poetry. In fact, she was often portrayed as a mad recluse; however, in her poem "Much Madness is divinest Sense" she may be presenting a defense of her solitude. For, her mention of "the Majority" in the fourth line certainly points to Emerson's words about "Society" and its demand for conformity that poses no problems:
Assent--and you are sane--
Demur--you're straightway dangerous--
And handled with a Chain--
These last three lines of Dickinson's also call to mind the poet T.S. Eliot, who was declared insane and institutionalized for a period during World War II because he had "demurred" against the conventional wisdom.
"Society," that body of governing people who set the standards of normalcy, dictates, as Emerson declared, that thinking away from conventional lines is "madness." But, it is those who think creatively and independently, who often perceive reality and even the future with a "discerning eye," that understand the truth of what happens and will happen. Because they are a threat to the stability of their societies, these people are often ostracized or declared to be abnormal and "mad."