A confession of hopes, dreams, failures, and sins, The Flowers of Evil attempts to extract beauty from the malignant. Unlike traditional poetry that relied on the serene beauty of the natural world to convey emotions, Baudelaire felt that modern poetry must evoke the artificial and paradoxical aspects of life. He thought that beauty could evolve on its own, irrespective of nature and even fueled by sin. The result is a clear opposition between two worlds, "spleen" and the "ideal." Spleen signifies everything that is wrong with the world: death, despair, solitude, murder, and disease. (The spleen, an organ that removes disease-causing agents from the bloodstream, was traditionally associated with malaise; "spleen" is a synonym for "ill-temper.") In contrast, the ideal represents a transcendence over the harsh reality of spleen, where love is possible and the senses are united in ecstasy.

The ideal is primarily an escape of reality through wine, opium, travel, and passion. Dulling the harsh impact of one's failure and regrets, the ideal is an imagined state of happiness, ecstasy, and voluptuousness where time and death have no place. Baudelaire often uses erotic imagery to convey the impassioned feeling of the ideal. However, the speaker is consistently disappointed as spleen again takes up its reign. He is endlessly confronted with the fear of death, the failure of his will, and the suffocation of his spirit. Yet even as the poem's speaker is thwarted by spleen, Baudelaire himself never desists in his attempt to make the bizarre beautiful, an attempt perfectly expressed by the juxtaposition of his two worlds. As in the poem "Carrion," the decomposing flesh has not only artistic value but inspires the poet to render it beautifully.

Women are Baudelaire's main source of symbolism, often serving as an intermediary between the ideal and spleen. Thus, while the speaker must run his hands through a woman's hair in order to conjure up his ideal world, he later compares his lover to a decomposing animal, reminding her that one day she will be kissing worms instead of him. His lover is both his muse, providing ephemeral perfection, and a curse, condemning him to unrequited love and an early death. Women, thus, embody both what Baudelaire called the elevation toward God and what he referred to as the gradual descent toward Satan: They are luminous guides of his imagination but also monstrous vampires that intensify his sense of spleen, or ill temper. The result is a moderate misogyny: Baudelaire associates women with nature; thus, his attempt to capture the poetry of the artificial necessarily denied women a positive role in his artistic vision.

Baudelaire's poetry also obsessively evokes the presence of death. In "To a Passerby," a possible love interest turns out to be a menacing death. Female demons, vampires, and monsters also consistently remind the speaker of his mortality. However, the passing of time, especially in the form of a newly remodeled Paris, isolates the speaker and makes him feel alienated from society. This theme of alienation leaves the speaker alone to the horrific contemplation of himself and the hopes of a consoling death. Baudelaire further emphasizes the proximity of death through his reliance on religious imagery and fantasy. He earnestly believes that Satan controls his everyday actions, making sin a depressing reminder of his lack of free will and eventual death.

Finally, elements of fantastical horror--from ghosts to bats to black cats-- amplify the destructive force of the spleen on the mind. Baudelaire was inspired by Edgar Allen Poe's Tales of Mystery and Imagination, and he saw Poe's use of fantasy as a way of emphasizing the mystery and tragedy of human existence. For example, Baudelaire's three different poems about black cats express what he saw as the taunting ambiguity of women. Moreover, the presence of tortured demons and phantoms make the possibility of death more immediate to the speaker, prefiguring the fear and isolation death will bring.