Kaṭha Upaniṣad · 2.3.7
इन्द्रियेभ्यः परं मनो मनसः सत्त्वमुत्तमम् । सत्त्वादधि महानात्मा महतोऽव्यक्तमुत्तमम् ॥ ७ ॥
indriyebhyaḥ paraṃ mano manasaḥ sattvamuttamam | sattvādadhi mahānātmā mahato'vyaktamuttamam || 7 ||
Beyond the senses is the mind; beyond the mind is the intellect; beyond the intellect is the Great Ātman; beyond the Great Ātman is the Unmanifest.
This hierarchical scale describes the subtle levels of existence, from the most external to the most internal. The indriya (senses) perceive the external world. The manas (mind) coordinates sensory impressions. The sattva (intellect/buddhi) discriminates and decides. The mahān ātman (great Ātman) is the principle of cosmic intelligence. The avyakta (unmanifest) is the primordial undifferentiated nature.
Each level is the adhi (support) of the previous. Without the intellect, the mind cannot function; without the mind, the senses cannot perceive. But the true Ātman is beyond all this hierarchy; it is the witness of all these levels without being identified with any.
For the yogi, this means that meditation must transcend even the intellect. We do not seek mental clarity or conceptual understanding; we seek that which precedes all understanding, the pure conscious presence in which all experience arises. The avyakta is the gateway to the absolutely transcendent.