Unamuno created in "La Tía Tula" a character out of the ordinary, with which he set out to explore the virginity-motherhood dichotomy, so linked to the foundations of Christianity. In trying to reconcile these two opposing tendencies, he creates a paradoxical, complex, debatable character that can provoke reactions as disparate as admiration and repulsion.

The plot of the novel, one of the best known of Unamuno, is based on the anthropological practice of levirate and sororate in a context of sexual repression.