The tone of Uncle Tom's Cabin moves from scathingly ironic to melodramatic, to sincere and sentimental to condescending. All of these tones convey Stowe's condemnation of slavery.
The novel's narrator spares no bitterness in her ironic condemnation of slave traders or of preachers and politicians who promote slavery. For example, about a trader who has taken a slave's baby to be sold and then justified the action as humane, she says the following:
The trader had arrived at that stage of Christian and political perfection which has been recommended by some preachers and politicians of the north, lately, in which he had completely overcome every humane weakness and prejudice.
But at other times, the tone shifts to melodramatic. When Eliza, carrying her four-year-old son and with the slave catchers on her heels, makes the dangerous journey across the ice floes at night on the Ohio River, readers are kept on the edge of their seats because of the heightened drama.
Stowe's narrative also frequently adopts a tone of sincerity when she describes the lives of the slaves, such as the cozy cabin where Tom lives with his family at the beginning of the novel:
In front it had a neat garden-patch, where, every summer, strawberries, raspberries, and a variety of fruits and vegetables, flourished under careful tending. The whole front of it was covered by a large scarlet bignonia and a native multiflora rose, which, entwisting and interlacing, left scarce a vestige of the rough logs to be seen. Here, also, in summer, various brilliant annuals, such as marigolds, petunias, four-o’clocks, found an indulgent corner in which to unfold their splendors, and were the delight and pride of Aunt Chloe’s heart.
Victorian audiences loved sentiment or emotion, especially deathbed scenes, and Stowe uses this, such as when the angelic Little Eva dies surrounded by people of all backgrounds, equally devastated by the pure young girl's passing.
Finally, Stowe, although her heart was in the right place, can also be condescending in describing the slaves, in ways that sound cringeworthy and racist to modern ears:
Tom, who had the soft, impressible nature of his kindly race, ever yearning toward the simple and childlike, watched the little creature [Eva] with daily increasing interest.
However, the author's intention was to appeal to white people, those who had the power to end slavery.