This paper discusses the reliability of the criteria for determining Śaṅkara’s authorship established by Paul Hacker. His analysis of terminological peculiarities is based on only one of Śaṅkara’s works—the commentary on the Brahma-Sūtras. Therefore, doubt arises as to whether these criteria also apply to other works that we can claim to be authentic. First, it will be argued that the commentaries on the Bṛhadāraṇyaka- and Taittirīya-Upaniṣad are works that can be—with reasonable certainty—considered authentic. When applied to these two works, Hacker’s (...) criteria work remarkably well, and the commentaries on the Taittirīya- and Bṛhadāraṇyaka-Upaniṣad share the same terminological and conceptual features with the Brahma-Sūtra-Bhāṣya. Moreover, in most cases, it is possible to distinguish the usage of some terms and concepts from Sureśvara and Padmapāda. On the other hand, Sureśvara and Padmapāda use some of these terms in a quite similar way as Śaṅkara, but differently than the later Advaitins, indicating that a sharp line between Śaṅkara on the one hand and Sureśvara and Padmapāda on the other cannot be drawn in many cases. Also, the writings of these authors—especially Padmapāda—represent a transitional phase in the development of certain Advaita Vedānta concepts although the outlines of some peculiarities by which the later Advaita Vedānta differs from Śaṅkara can already be found sketched by Śaṅkara himself. (shrink)