 The theory of the syllogism (qiyās), in its main divisions, occupies a prominent part in all of Avicenna’s logical works. The doctrinal skeleton remains the same in spite of a significant re-arrangement of the material, especially in the Išārāt. In the works of the middle period, especially the Nağāt and the extensive treatment of the Qiyās, Avicenna follows the path charted by the Prior  Analytics.[13]