Bhagavad Gita · Karma YogaChapter 3, Shloka 42 (3.42)

A ladder — from outside to inside. Body → senses → mind → buddhi → "sah".

"Sah" — three readings (this is one of the important differences of interpretation in this chapter):

• Shankaracharya (and Madhusudana): buddheḥ paratas tu saḥ buddher draṣṭā paramātmā — beyond the buddhi, the witness of the buddhi — the Supreme Self (the self). This is the embodied one whom desire (3.40) deludes through the seats of the senses and the rest. Madhusudana here quotes the Katha Upanishad — indriyebhyaḥ parā hy arthā arthebhyaś ca paraṃ manaḥ….
• Madhva: beyond the buddhi — and, according to the Katha Upanishad (avyaktāt puruṣaḥ paraḥ), beyond even the unmanifest — the Supreme Person, Hari; and he regards knowledge of him with all his qualities as the means to liberation.
• Acharya Ramanuja: buddheḥ api yaḥ paraḥ sa kāmaḥ — that which is "para" (more powerful) than even the buddhi is desire! His argument: if the senses are engaged with objects, there is no knowledge of the self; if the senses stop but the mind is on objects, still none; if the mind too stops but the buddhi decides wrongly, still none; and if all of them stop, but icchā-paryāyaḥ kāmo rajaḥ-samudbhavaḥ — desire, which is another name for wanting and is born of rajas, remains, it engages all of them in objects again and blocks knowledge of the self. Therefore desire is more powerful than even the buddhi.