Ban Zhao was the most learned woman of the Han and the tradition's treatment of her is instructive. She completed the Book of Han, the dynastic history her father Ban Biao began and her brother Ban Gu left unfinished at his death in prison, writing the astronomical treatise and eight chronological tables herself; she was summoned to the palace to instruct the empress and the ladies of the court, and senior scholars are recorded as her students. She also wrote Nüjie, Lessons for Women, in seven short chapters, which argues that girls should be educated — on the grounds that a wife who cannot read cannot properly serve — and which sets out humility, deference and the four womanly virtues in terms that later centuries hardened into an instrument. Modern scholarship is genuinely divided: some read her as making the strongest argument available for female literacy within the constraints she had, others as supplying the canonical text for female subordination. Both readings are supported by the document, and the tradition subsequently quoted only one of them.