Raḍī l-Dīn al-ʾAstarābāḏī (d. ca. 1289) seems to be different from other Arab grammarians; I claim that the unique character of his Šarḥ al-Kāfiya can be explained, at least partially, by influences from other Islamic sciences, especially logic. Although such influences can also be found in earlier grammarians’ writings, in Šarḥ al-Kāfiya they are particularly strong, so much so as to often make the understanding of the text difficult or impossible without acquaintance with other Islamic sciences. This point can be demonstrated by investigating al-ʾAstarābāḏī’s multiple discussions on definitions.
The current article surveys the following subjects related to the theory of definition in Šarḥ al-Kāfiya: various types of definitions (ḥadd ḥaqīqī, ḥadd rasmī, ḥadd lafẓī), the structure of a complete definition (jins+faṣl), and criteria for a complete definition: coextensiveness and conversion, separate definitions for separate concepts, an accurate formulation and avoiding circularity. I use treatises by al-Ġazālī and Ibn Sīnā to elucidate some terms and arguments in Šarḥ al-Kāfiya, that are unclear otherwise.