2003, 2nd unrevised edition, 186 pp. german, 134 pp. arabic text.
In his work, Prof. van Ess deals with the heretic writings of the muʿtazili scholar an-Nāšī (d. 293/905). These writings are Kitāb Uṣūl an-Niḥal and Kitāb al-Ausaṭ written by an-Nāšī. These are found in two manuscripts, which are presented and analysed by van Ess.
Prof. Josef van Ess wrote his dissertation about Islamic mysticism at the University Bonn, his habilitation treatise dealt with the cognitive science in the islamic scholasticism.