After Ulugh Beg's death in 853/1449, Qūshjī, while in Herat, wrote his theological (kalām) work Šarḥ Tajrīd al‐ʿaqāʾid, a commentary on Naṣīr al-Dīn al-Ṭūsī’s (d. 672/1274) Tajrīd al‐ʿaqāʾid, which Qūshjī presented to the Timurid ruler Abū Saʿīd. Qūshjī puts forth new views on a number of issues; among these is questioning astronomy's dependence on Aristotelian physics, thus raising the possibility of the Earth’s rotation.