Fuller touches on many topics in her book so much so that many (white male) critics defined Woman in the Nineteenth Century a "glorious confusion". Yet, the theme which she develops more fully is certainly women's position of inferiority when compared to men in the nineteenth century. Men refuse to acknowledge women's spirituality and thus hinder their intellectual growth. Because of this attitude, women cannot fully realize their God-given potential. Fuller's argument also linked the battle for women's rights to abolitionism, stating that those who thought that slavery was wrong could certainly not approve of the submission of women. The liberation of women should be considered a right, not as a mere concession. This idea influenced the movement for women's suffrage.
Although Fuller clearly identifies the conflict between men and women in the nineteenth century, she introduces a touch of skepticism against the binary opposition when she says that "there is no wholly masculine man, no purely feminine woman."