In TULb one of the major themes in the novel is the balance between opposites and the morality of one side verves it’s opposite or making a value judgement on either side. One part has to be positive or good and it’s related opposite must therefore be negative or bad. I think Toaists and Manichaeans had a similar philosophy of moral dualism for instance- yin vs yang. The narrator explains that eternal return, the recurrence of every experience forever, is a heavy burden weighted with moral implications and truth. According to Parmenides, a Greek philosopher, the narrator hypothesizes that lightness of being—having no responsibility or moral obligations is the opposite of being burdened so it must be positive and eternal return, or the heaviness of being is negative. But he is unsure if that is true. (Is it? Must lightness/weight of being be deemed good or bad or can't it just be a fact of life?) Other dual aspects of relationships mentioned in the book include: sacrifice and guilt, fear of women and “erotic friendship” with them, trust and betrayal, male verses female sexuality, body and soul, etc. Tomas himself is described as a conjunction of “two worlds.” He is both a romantic lover and a debacherous womanizer.