TAIPEI, Taiwan — It is an age-old arrangement, and one that is usually implicit: Parents pay for their children’s educations, and hope that in their old age the children will support them.

But in a case that made its way to Taiwan’s highest court, a mother who had financed her son’s dental training sued him, asserting that he had broken a written agreement to support her from the proceeds of his dental practice.

On Tuesday, the Supreme Court sided with his mother.

The case attracted considerable attention because the mother and son had put down in a written contract — signed when he was 20 — what is often left unsaid, particularly in a heavily Confucian-influenced society that emphasizes filial piety. The principle is backed up by law in Taiwan, where adults are legally prohibited from abandoning their parents.

Each side advanced arguments: The mother urged the court to enforce the contract. The son maintained that he had already paid his mother $1 million and should not have to pay her more.