dayyan—i.e., judge of a rabbinical court—in Muslim Spain and author of a highly influential and popular work of ethical guidance.

About 1080 Bahya wrote, in Arabic, Al-Hidāyah ilā-farāʾ id al-qulūb (“Duties of the Heart”). In a rather inaccurate 12th-century translation into Hebrew by Judah ben Joseph ibn Tibbon, Ḥovot ha-levavot, it became a widely read classic of Jewish philosophic and devotional literature. An English translation, Duties of the Heart (1925–47; reprinted 1962), was completed by Moses Hyamson.

Via the Islāmic mystics, known as Ṣūfīs, Bahya was influenced by Neoplatonism as to the nature of God and the soul's quest for him. From the Islāmic system of dialectical theology called kalām he borrowed proofs for the existence of God.

Critical of his predecessors who, of the two requirements of religion, had emphasized the “duties of the body” to the neglect of the “duties of the heart,” Bahya wrote his book to restore the proper balance. The “duties of the body” are obligatory outward actions—religious ritual and ethical practice—while the “duties of the heart” are the attitudes and intentions that determine the state of a person's soul and alone give value to his acts.