Sabina also emigrated to Switzerland and has been enjoying artistic success in Geneva. She and Tomas meet in a hotel room; Sabina wears nothing but lingerie and a bowler hat, and the two fall into each other's arms. Tomas continues his infidelities for mo nths after arriving in Zurich. One day, he finds a letter from Tereza, saying that because she knows she is a burden to him, she has left him to return to Prague. Since the Czech borders have been closed in their absence, Tereza's return to Prague means s he will not be allowed to leave the country again.
Tomas attempts to enjoy his newly recovered freedom and tells himself things had to end this way. He lasts five days before he tells his supervising doctor that he must return to Prague. A Beethoven motif plays in his mind: Ess muss sein, or "It mu st be." The narrator notes that Beethoven clearly viewed weight as positive.
In Prague, however, Tomas begins to wonder if he should have stayed in Zurich. He wonders how long his intense longing for Tereza would have lasted; perhaps he could have waited for the pain to subside. Lying next to her in bed, he thinks unhappily that n othing more glorified than chance and accident brought the couple together.
This first section introduces and establishes Tomas's character, and his understanding of his own relationship with Tereza. Tomas seems preoccupied with the same questions that interest the narrator; he ponders, as the narrator does at the beginning of th e novel, the philosophical question of lightness versus weight, and wonders how the question applies to his everyday life. Although Tomas may seem to be a selfish man and an objectionable character, Kundera manages to make him immensely sympathetic. His womanizing is explained less as a conscious choice having to do with conquest, social status or machismo, than as an integral part of his personality and thought. He enjoys lightness and freedom, and resists attempts made by others to trap him. Tomas is a natural individualist. He is also acutely compassionate, however, and cannot passively watch genuine suffering.
Tomas's relationship with Tereza is outlined as a conflict between lightness and heaviness: Tomas wishes to be light, to take his sexuality and exploits lightly and to be free to enjoy his career and interests. Tereza wants a weightier brand of love. She asks for Tomas to devote himself physically and emotionally to her alone. Her intense need for Tomas's devotion prompts her to read his letters and resent the time he spends away from her.
Just as Tereza cannot take love or sexuality lightly, she does not take her work lightly; her dissident work during the occupation interests her passionately, and she seems more attached to her homeland than does Tomas.
Kundera symbolizes Tereza's heaviness by associating her with heavy objects. The suitcase she carries seems to contain her whole life, a burden Tomas must also bear. Tereza also introduces Tomas to Beethoven and the profound heaviness of his music. In add ition, the novel Tereza reads when she first arrives and after which the couple name their dog is Anna Karenina. This novel, with its tragic tale of love, suffering and suicide both foreshadows the kind of love Tereza offers Tomas, and hints constantly at the threat of suicide.
That Kundera portrays both the light Tomas and the heavy Tereza as sympathetic characters points to the sincerity of the philosophical dilemma: both lightness and heaviness seem meaningful and desireable.
Tereza's heaviness begins to seep into Tomas's lightness; he finds a new love for Beethoven, and performs a grandiose, romantic act of sacrifice by returning to his occupied country to be with Tereza. Clearly, Tereza's heaviness fills Tomas's life with a weight and meaning he lacked before. She makes him feel, to some extent, that their life together has meaning. Still, Tomas's long-held belief tells him that life is light; because we cannot make two sets of life decisions and compare the results, the pat h we happened to choose cannot be considered "weighty" or meaningful. He is well aware of the idea that one can never know if one made the right choice, since there is never a point of comparison.
Tomas decides to stay with Tereza because the pair love one another; despite this love, however, they make one another unhappy. This knowledge tortures Tomas, who wonders whether he should have sent Tereza away when she first met him in Prague, or if he should have remained in Switzerland without her.