Kaṭha Upaniṣad 137

137

tatraivaṃ sati yas tv avijñānavān yasya buddhyākhyaḥ sārathir avijñāno 'nipuṇo 'vivekī pravṛttau ca nivṛttau ca bhavati, yathetaro rathacaryāyām ayuktenāpragṛhītenāsamāhitena manasā pragrahasthānīyena sadā yukto bhavati, tasyākuśalabuddhisārather indriyāṇy aśvasthānīyāny avaśyāny aśakyanivāraṇāni duṣṭāśvā adāntāśvā ivetarasārather bhavanti ///1,3.5 //

Shankara’s Commentary:
Com.—This being so, of that driver known as Buddhi, who is not capable of discrimination as to what is to be done or omitted to be done, as the other driver in the guiding of his chariot has a mind like the reins of a chariot not well-grasped by the driver, i.e., uncontrolled by the intellect; of that incompetent driver, i.e., intellect, the senses which stand in the place of the horses become unruly and uncontrollable, as the vicious horses of the other driver.