"Much Madness is Divinest Sense" is a short poem by Emily Dickinson. The poem reads as follows:

Much Madness is divinest Sense—

To a discerning Eye—

Much Sense—the starkest Madness—

’Tis the Majority

In this, as all, prevail—

Assent—and you are sane—

Demur—you’re straightway dangerous—

And handled with a Chain—

Summary: A perceptive person can tell that sometimes madness is actually sensible and sometimes being sensible is actually mad. The majority calls the shots on this, as on everything else. Agree with the majority, and they will call you sane; disagree with them, and they will call you crazy.

The central paradox of the poem is the idea that madness could ever be sensible or vice versa. What one needs to understand the paradox is the reference in line two to "a discerning Eye." The narrator clearly believes that the majority is not discerning, else agreeing with them (and being called sensible by them) wouldn't qualify a person -- in the speaker's eyes -- as being mad; further, since the majority is not discerning, disagreeing with them makes a person sensible, to the speaker.