Sworn sisters are a group of women in the same stage of life who are contracted to be friends and support each other, but the group is dissolved when they marry or grow old. A
laotong relationship, on the other hand, lasts for life (and supposedly even for eternity). Notice that marriage here is described as something transactional and entirely unemotional. This idea will be questioned throughout the novel, and even now as Lily remarks occasionally how happy Aunt and Uncle seem to be as a married couple.