The second component of antaḥkaraṇa is buddhi, also known as intellect, which is next to mind. Mostly buddhi is not considered as different from the mind. But Kṛṣṇa says in Bhagavad Gītā (III.42), “The senses are said to be greater than the body; but greater than the senses is the mind; greater than the mind is buddhi. Self is greater than buddhi.” This is beautifully explained in Kaṭha Upaniṣad (I.iii.3-7), which says, “Ātman (Kūṭastha) is seated in a chariot, drawn by horses known as sensory organs or indriya-s. Mind is compared to the reins and the driver of the chariot is intellect (buddhi). Ātman as the owner of the chariot, commands the driver. Driver, the intellect obeys the commands of his master, Ātman. Driver carries out the commands of his master, atman by controlling the reins. Reins in turn control the horses. But the question is when atman is veiled by the afflictions of sensory influences, how it can make commands. The uniqueness of the intellect is its capacity to discriminate between good and bad. Only this singular quality makes the intellect superior to mind.”
Though antaḥkaraṇa is considered as one, its four components mind, intellect (buddhi), consciousness and ego are considered as its vṛtti, a complex formation, which requires separation into various parts, as distinguished from a simple or uncompounded form. It is only the buddhi that conveys the objects of experience to Kūṭastha (individual soul). Suppose there is an apple in front of person named X. The mind of X sees the apple and desire to have this apple is caused in the mind itself. As buddhi gets the reflection of Kūṭastha, it perceives apple as an apple. There is powerful relationship between Kūṭastha and buddhi. However, the reflection of Kūṭastha in the buddhi is not Kūṭastha itself. It is only a reflection. When the apple is taken away, the mind cannot see it and buddhi cannot experience it. Still Kūṭastha is present as it is, without any change in its Nature. But Kūṭastha has belief, firm conviction, trust, faith, assurance and certainty (these combined together is known as pratyaya) in buddhi. Again it must be remembered that Kūṭastha does not do anything; it simply exists. When the reflection of Kūṭastha falls on buddhi, the doership of buddhi is superimposed on Kūṭastha. At this time, Kūṭastha falsely appears as the perceiver. Therefore, it is only pratyaya of buddhi which causes perception of shapes and forms. But it is wrongly believed that Kūṭastha is the perceiver and in reality, Kūṭastha does not do anything. It remains only as a witness. We wrongly consider buddhi as Kūṭastha because of inherent māyā and avidyā in Kūṭastha. Buddhi is the one, which decides the true nature of an object.
Tattvabodha describes the intellect as “niścayātmikā buddhiḥ”. Niścayātmikā refers to the inherent nature of the intellect viz. its form of certainty. The indecisive nature of the mind now looks up to intellect for guidance. If the mind is the disciple, then the intellect is the guru. In times of confusion, like the disciple seeking guidance from his spiritual preceptor, mind also takes recourse to the intellect in order to overcome its state of indecisiveness. Intellect is an evolution of the guṇa-s (which will be discussed subsequently), though it has more of sattva quality. This can be understood from the fact that intellect is the guru of the mind. Intellect not only guides the mind by giving decisions, but also helps the mind in association with one’s conscience to establish the divine commune. Though intellect is a refined product of the mind, it does not mean that it is supreme to the mind. Intellection is relative in value only till the Brahman is realized. After Self-realization, nothing is required.