A Talmudist of high repute, he was appointed in 1138 dayyan at Cordova, which office he held conjointly with Maimon, father of Maimonides, until his death.
Though not an original thinker (at every point of his system he borrows very largely from Solomon Ibn Gabirol's Fons Vitæ),[2] he shows himself to be thoroughly familiar with the philosophical and scientific literature of the Arabs, and imposes the stamp of his own individuality on the subjects treated.
After stating the elementary and primary principles of the knowledge of God, the acquisition of which is the highest duty of man, and explaining how the human soul builds up its conception of things, Joseph treats, in the manner of the Arabic Aristotelians, of matter and form, of substance and accident, and of the composition of the various parts of the world.
Further, he presents analogies to the characteristics of things: his erect figure resembles that of the terebinth; his hair, grass and vegetation; his veins and arteries, rivers and canals; and his bones, the mountains.
Indeed, he possesses the characteristics of the animals: he is brave like a lion, timid like a hare, patient like a lamb, and cunning like a fox.
Like Saadia Gaon and Bahya ibn Paquda, though more precisely and more systematically, Joseph proves the creation of the world (and consequently the existence of a Creator) from its finiteness.
He criticizes the theory of the Motekallamin (as expounded in the Machkimat Peti of Joseph ha-Ro'eh), who assert that the world was produced by the created will of God.
Man must serve God with all his heart, and carry out all His precepts, though, owing to the weakness of his intellect, he may not grasp the reason for some of them.
Although paying a high tribute to Joseph's learning, Maimonides, in his letter addressed to Samuel ibn Tibbon (Pe'er ha-Dor, p. 28b), acknowledges that he has never seen the work, in which, he believes, are expounded the teachings of the Brethren of Sincerity.
Joseph was the author also of an Arabic work on logic, entitled Al-'Uyun wal-Mudhakarat, quoted in the Olam Katan.