Definition of Mood
The mood throughout The Souls of Black Folk is somber, and rightfully so, given its content. This remains fairly consistent over the course of the book, with brief shifts into more informative sections that are relatively neutral when it comes to mood.
In the particularly somber Chapter 11, Du Bois relays his emotions upon the birth of his first child:
Within the Veil was he born, said I; and there within shall he live, —a Negro and a Negro's son. Holding in that little head—ah, bitterly!—the unbowed pride of a hunted race, clinging with that tiny dimpled hand—ah, wearily!—to a hope not hopeless but unhopeful, and seeing with those bright wondering eyes that peer into my soul a land whose freedom is to us a mockery and whose liberty is a lie.