Tomas belongs to the Czech intellectual class, which was silenced after the Soviet invasion of Prague. An internationally known surgeon, Tomas is stripped of his career because he refuses to renounce an anti-Czech Communist article he wrote. This single article puts him in grave danger, although he is not a committed or active political dissident. Ideally, Tomas would like to avoid political parties and society altogether in favor of being a free agent and independent thinker who acts as he chooses. After losing the privilege of practicing medicine, Tomas becomes first a window washer and then a farmer, descending to the lower rungs of society in search of a peaceful life.
As a man, Tomas attempts to practice a philosophy of lightness. He considers sex and love two separate and unrelated entities; he sleeps with many women, and loves one woman (Tereza), and sees no problem with the simultaneous existence of these two ac tivities.
Although Tomas is an intellectual and a thinker, he is no romantic idealist like Simon or Franz. His lover Sabina calls him the "complete opposite of kitsch," or the complete opposite of the shiny, perfect ideals of politics and love. Tomas cannot take seriously the laws on which politics and romantic fidelity are based. His pragmatism, experience, and individualism make him unwilling to identify himself as a political liberal or as a faithful husband. Consequently, most of the characters misi nterpret Tomas; the police and his hospital colleagues think him a dissident, and dissidents think him a coward.
Tomas's character does not fundamentally change over the course of the novel. Instead, Tomas gains a modicum of heaviness. He also grows a little more cynical, as he becomes uncertain of his once firm views on life and being. His love for Tereza and eventual exile to the countryside curb his erotic adventures, but he never necessarily loses the desire for sex with many anonymous partners, or the conviction that such a desire is no crime.
Tereza represents purity and innocence that lead Tomas to see her as "child put in a basket and sent downstream" for him to find. Tereza is waiting for someone like Tomas to appear even before she meets him; even after she meets him, his constant betrayals mean she must frequently wait for him to return. The two love each other deeply, but make each other miserable. Tereza is not vulgar or kitsch in any easily recognizable sense; however, where Tomas and Sabina are light, she is heavy.
Tereza does not damn Tomas for his infidelities, and instead characterizes herself as weaker than him. Her "strongest" moment comes when she leaves Zurich and Tomas and returns to Prague alone, sacrificing her own happiness to relieve Tomas of the burden of her love. Precisely because of her intelligence and compassion, Tereza presents a kind of heaviness Tomas cannot easily dismiss.
Dissident activism interests Tereza. She finds meaning, beauty, and weight in her courageous work as a photo-journalist during the Soviet takeover of Prague; unlike most of the European political left, however, Tereza admits to the existence of naiveté in her political work.
Tereza changes considerably during the course of The Unbearable Lightness of Being, as she is increasingly forced to recognize the impossibility of her youthful dreams. Nothing remains as black and white as she feels it should be; Tereza even comes to admire her archrival Sabina and feels Sabina's powerful sensuality, although she knows Sabina is Tomas's beloved mistress. Just as Tomas must question his lightness, Tereza must question her heaviness.
Sabina represents extreme lightness of being. Early on, faced with the ugliness and kitsch in life, from her father's repressive patriarchal home to the totalitarian art styles pressed at her art school, Sabina declares war on the ugly and unoriginal through her paintings and lifestyle. Sabina's life is described as a series of betrayals: "Betrayal means breaking ranks and going off into the unknown. Sabina knew of nothing more magnificent..." Her pursuit of freedom leads her to complete isolation and freedom in America.
Sabina's love affair with Tomas is based on their mutual lightness. There is no element of the domestic or usual romantic kitsch in their relationship; instead the two share a playful eroticism. However, like Tomas, Sabina is drawn to the intensity of hea vier spirits. Tereza charms Sabina, and she falls in love with Franz, both of whom are heavy characters. Sabina also feels the occasional charm of the kitsch she so detests, admitting she cries at films of prodigal children and homecomings.
Sabina understands that her extreme choices might leave her irrelevant and alone. This knowledge makes Sabina uneasy; in America, she wonders whether she has anything left to betray. She will also never know what could have happened had she not betrayed so many people over the years; the unbearable lightness of being is that each decision is faced once and only one possible outcome tried. Tomas chose Tereza and burden, Sabina chose freedom and total lightness; neither can know whether they chose correctly.
Sabina also has special relevance as a permanent and ambivalent exile. Kundera, like Sabina, never returned to his homeland.
Franz is incapable of lightness. He creates meaning in his life by attaching solemn weight and importance to concepts and events. Thus, he adores marches and lives for the strong emotions of love and political conviction. Unlike Tereza, he is naive en ough to believe that his approach is the only possible one.
Franz can be described as kitsch in his tastes and ideas, but his character is more sympathetic than vulgar, for he is also a kind and compassionate man. He makes difficult decisions out conviction, and is noble and gentle, if impossibly unperceptive. Onl y at the very end of his life does he suspect he may have made some errors in judgment; this realization comes too late, however, as his idealism, naiveté and inability to understand his surroundings lead to a meaningless death in Bangkok.