Existence of God
In Abū Qurrah's "Questions of Priest Musa", in the course of its first two discourses ("On the Existence of God and the True Religion") he used a thought experiment in which he imagined himself having grown up away from civilization (on a mountain) and descending to 'the cities' to inquire after the truth of religion: an attempt to provide a philosophical argument in support of Chalcedonian Christianity from first principles.